Improve handling of manual downloads; "Continue" now rechecks files

Now always asks the user before proceeding past the point where optional mods could be selected and configured
When updating files, the hash is checked so an update isn't redownloaded if it already exists
Added DevMain file for running in a dev environment

.gitignore

@@ -1,9 +1,9 @@
 
-# Created by https://www.gitignore.io/api/java,gradle,intellij
-# Edit at https://www.gitignore.io/?templates=java,gradle,intellij
+# Created by https://www.toptal.com/developers/gitignore/api/java,gradle,intellij+all
+# Edit at https://www.toptal.com/developers/gitignore?templates=java,gradle,intellij+all
 
-### Intellij ###
-# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio and WebStorm
+### Intellij+all ###
+# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio, WebStorm and Rider
 # Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839
 
 # User-specific stuff
@@ -33,6 +33,9 @@
 # When using Gradle or Maven with auto-import, you should exclude module files,
 # since they will be recreated, and may cause churn.  Uncomment if using
 # auto-import.
+# .idea/artifacts
+# .idea/compiler.xml
+# .idea/jarRepositories.xml
 # .idea/modules.xml
 # .idea/*.iml
 # .idea/modules
@@ -72,13 +75,18 @@ fabric.properties
 # Android studio 3.1+ serialized cache file
 .idea/caches/build_file_checksums.ser
 
-### Intellij Patch ###
-# Comment Reason: https://github.com/joeblau/gitignore.io/issues/186#issuecomment-215987721
+### Intellij+all Patch ###
+# Ignores the whole .idea folder and all .iml files
+# See https://github.com/joeblau/gitignore.io/issues/186 and https://github.com/joeblau/gitignore.io/issues/360
 
-# *.iml
-# modules.xml
-# .idea/misc.xml
-# *.ipr
+.idea/
+
+# Reason: https://github.com/joeblau/gitignore.io/issues/186#issuecomment-249601023
+
+*.iml
+modules.xml
+.idea/misc.xml
+*.ipr
 
 # Sonarlint plugin
 .idea/sonarlint
@@ -127,4 +135,4 @@ gradle-app.setting
 ### Gradle Patch ###
 **/build/
 
-# End of https://www.gitignore.io/api/java,gradle,intellij
+# End of https://www.toptal.com/developers/gitignore/api/java,gradle,intellij+all

.idea/codeStyles/codeStyleConfig.xml

@@ -1,5 +0,0 @@
-<component name="ProjectCodeStyleConfiguration">
-  <state>
-    <option name="PREFERRED_PROJECT_CODE_STYLE" value="Default" />
-  </state>
-</component>

.idea/inspectionProfiles/Project_Default.xml

@@ -1,36 +0,0 @@
-<component name="InspectionProjectProfileManager">
-  <profile version="1.0">
-    <option name="myName" value="Project Default" />
-    <inspection_tool class="JavaDoc" enabled="true" level="WARNING" enabled_by_default="true">
-      <option name="TOP_LEVEL_CLASS_OPTIONS">
-        <value>
-          <option name="ACCESS_JAVADOC_REQUIRED_FOR" value="none" />
-          <option name="REQUIRED_TAGS" value="" />
-        </value>
-      </option>
-      <option name="INNER_CLASS_OPTIONS">
-        <value>
-          <option name="ACCESS_JAVADOC_REQUIRED_FOR" value="none" />
-          <option name="REQUIRED_TAGS" value="" />
-        </value>
-      </option>
-      <option name="METHOD_OPTIONS">
-        <value>
-          <option name="ACCESS_JAVADOC_REQUIRED_FOR" value="none" />
-          <option name="REQUIRED_TAGS" value="@return@param@throws or @exception" />
-        </value>
-      </option>
-      <option name="FIELD_OPTIONS">
-        <value>
-          <option name="ACCESS_JAVADOC_REQUIRED_FOR" value="none" />
-          <option name="REQUIRED_TAGS" value="" />
-        </value>
-      </option>
-      <option name="IGNORE_DEPRECATED" value="false" />
-      <option name="IGNORE_JAVADOC_PERIOD" value="true" />
-      <option name="IGNORE_DUPLICATED_THROWS" value="false" />
-      <option name="IGNORE_POINT_TO_ITSELF" value="false" />
-      <option name="myAdditionalJavadocTags" value="wbp.parser.entryPoint" />
-    </inspection_tool>
-  </profile>
-</component>

.idea/jarRepositories.xml

@@ -1,20 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="RemoteRepositoriesConfiguration">
-    <remote-repository>
-      <option name="id" value="central" />
-      <option name="name" value="Maven Central repository" />
-      <option name="url" value="https://repo1.maven.org/maven2" />
-    </remote-repository>
-    <remote-repository>
-      <option name="id" value="jboss.community" />
-      <option name="name" value="JBoss Community repository" />
-      <option name="url" value="https://repository.jboss.org/nexus/content/repositories/public/" />
-    </remote-repository>
-    <remote-repository>
-      <option name="id" value="BintrayJCenter" />
-      <option name="name" value="BintrayJCenter" />
-      <option name="url" value="https://jcenter.bintray.com/" />
-    </remote-repository>
-  </component>
-</project>

.idea/misc.xml

@@ -1,10 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="EntryPointsManager">
-    <list size="1">
-      <item index="0" class="java.lang.String" itemvalue="com.google.gson.annotations.SerializedName" />
-    </list>
-  </component>
-  <component name="ExternalStorageConfigurationManager" enabled="true" />
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_8" default="false" project-jdk-name="11" project-jdk-type="JavaSDK" />
-</project>

.idea/vcs.xml

@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="VcsDirectoryMappings">
-    <mapping directory="" vcs="Git" />
-  </component>
-</project>

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2019
+Copyright (c) 2021 comp500
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -1,2 +1,2 @@
 # packwiz-installer
-An installer for launching packwiz modpacks with MultiMC.
+An installer for launching packwiz modpacks with MultiMC. You'll need [the bootstrapper](https://github.com/comp500/packwiz-installer-bootstrap/releases) to actually use this.

build.gradle.kts

@@ -1,28 +1,41 @@
+buildscript {
+	repositories {
+		mavenCentral()
+	}
+	dependencies {
+		classpath("com.guardsquare:proguard-gradle:7.1.0") {
+			exclude("com.android.tools.build")
+		}
+	}
+}
+
 plugins {
 	java
 	application
-	id("com.github.johnrengelman.shadow") version "5.0.0"
-	id("com.palantir.git-version") version "0.11.0"
-	id("com.github.breadmoirai.github-release") version "2.2.9"
-	kotlin("jvm") version "1.3.61"
+	id("com.github.johnrengelman.shadow") version "7.1.2"
+	id("com.palantir.git-version") version "0.13.0"
+	id("com.github.breadmoirai.github-release") version "2.2.12"
+	kotlin("jvm") version "1.6.10"
+	id("com.github.jk1.dependency-license-report") version "2.0"
+	`maven-publish`
 }
 
 java {
 	sourceCompatibility = JavaVersion.VERSION_1_8
 }
 
-dependencies {
-	implementation("commons-cli:commons-cli:1.4")
-	implementation("com.moandjiezana.toml:toml4j:0.7.2")
-	// TODO: Implement tests
-	//testImplementation "junit:junit:4.12"
-	implementation("com.google.code.gson:gson:2.8.1")
-	implementation("com.squareup.okio:okio:2.2.2")
-	implementation(kotlin("stdlib-jdk8"))
+repositories {
+	mavenCentral()
 }
 
-repositories {
-	jcenter()
+dependencies {
+	implementation("commons-cli:commons-cli:1.5.0")
+	implementation("com.moandjiezana.toml:toml4j:0.7.2")
+	implementation("com.google.code.gson:gson:2.8.9")
+	implementation("com.squareup.okio:okio:3.0.0")
+	implementation(kotlin("stdlib-jdk8"))
+	implementation("com.squareup.okhttp3:okhttp:4.9.3")
+	implementation("com.michael-bull.kotlin-result:kotlin-result:1.1.14")
 }
 
 application {
@@ -39,17 +52,59 @@ tasks.jar {
 	}
 }
 
-// Commons CLI and Minimal JSON are already included in packwiz-installer-bootstrap
+licenseReport {
+	renderers = arrayOf<com.github.jk1.license.render.ReportRenderer>(
+		com.github.jk1.license.render.InventoryMarkdownReportRenderer("licenses.md", "packwiz-installer")
+	)
+	filters = arrayOf<com.github.jk1.license.filter.DependencyFilter>(com.github.jk1.license.filter.LicenseBundleNormalizer())
+}
+
 tasks.shadowJar {
-	dependencies {
-		exclude(dependency("commons-cli:commons-cli:1.4"))
-		exclude(dependency("com.eclipsesource.minimal-json:minimal-json:0.9.5"))
+	exclude("**/*.kotlin_metadata")
+	exclude("**/*.kotlin_builtins")
+	exclude("META-INF/maven/**/*")
+	exclude("META-INF/proguard/**/*")
+
+	// Relocate Commons CLI, so that it doesn't clash with old packwiz-installer-bootstrap (that shades it)
+	relocate("org.apache.commons.cli", "link.infra.packwiz.installer.deps.commons-cli")
+
+	// from Commons CLI
+	exclude("META-INF/LICENSE.txt")
+	exclude("META-INF/NOTICE.txt")
+}
+
+tasks.register<proguard.gradle.ProGuardTask>("shrinkJar") {
+	injars(tasks.shadowJar)
+	outjars("build/libs/" + tasks.shadowJar.get().outputs.files.first().name.removeSuffix(".jar") + "-shrink.jar")
+	if (System.getProperty("java.version").startsWith("1.")) {
+		libraryjars("${System.getProperty("java.home")}/lib/rt.jar")
+		libraryjars("${System.getProperty("java.home")}/lib/jce.jar")
+	} else {
+		// Use jmods for Java 9+
+		val mods = listOf("java.base", "java.logging", "java.desktop", "java.sql")
+		for (mod in mods) {
+			libraryjars(mapOf(
+				"jarfilter" to "!**.jar",
+				"filter" to "!module-info.class"
+			), "${System.getProperty("java.home")}/jmods/$mod.jmod")
+		}
 	}
+
+	keep("class link.infra.packwiz.installer.** { *; }")
+	dontoptimize()
+	dontobfuscate()
+
+	// Used by Okio and OkHttp
+	dontwarn("org.codehaus.mojo.animal_sniffer.*")
+	dontwarn("okhttp3.internal.platform.**")
+	dontwarn("org.conscrypt.**")
+	dontwarn("org.bouncycastle.**")
+	dontwarn("org.openjsse.**")
 }
 
 // Used for vscode launch.json
 tasks.register<Copy>("copyJar") {
-	from(tasks.shadowJar)
+	from(tasks.named("shrinkJar"))
 	rename("packwiz-installer-(.*)\\.jar", "packwiz-installer.jar")
 	into("build/libs/")
 }
@@ -77,12 +132,38 @@ if (project.hasProperty("github.token")) {
 tasks.compileKotlin {
 	kotlinOptions {
 		jvmTarget = "1.8"
-		freeCompilerArgs = listOf("-Xjvm-default=enable")
+		freeCompilerArgs = listOf("-Xjvm-default=enable", "-Xallow-result-return-type", "-Xopt-in=kotlin.io.path.ExperimentalPathApi")
 	}
 }
 tasks.compileTestKotlin {
 	kotlinOptions {
 		jvmTarget = "1.8"
-		freeCompilerArgs = listOf("-Xjvm-default=enable")
+		freeCompilerArgs = listOf("-Xjvm-default=enable", "-Xallow-result-return-type", "-Xopt-in=kotlin.io.path.ExperimentalPathApi")
 	}
-}
+}
+
+if (project.hasProperty("bunnycdn.token")) {
+	publishing {
+		publications {
+			create<MavenPublication>("maven") {
+				groupId = "link.infra.packwiz"
+				artifactId = "packwiz-installer"
+
+				from(components["java"])
+			}
+		}
+		repositories {
+			maven {
+				url = uri("https://storage.bunnycdn.com/comp-maven")
+				credentials(HttpHeaderCredentials::class) {
+					name = "AccessKey"
+					value = findProperty("bunnycdn.token") as String?
+				}
+				authentication {
+					create<HttpHeaderAuthentication>("header")
+				}
+			}
+		}
+	}
+}
+

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-5.4.1-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-7.3.3-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists

src/main/java/link/infra/packwiz/installer/RequiresBootstrap.java

@@ -8,8 +8,6 @@ public class RequiresBootstrap {
 	public static void main(String[] args) {
 		// Very small CLI implementation, because Commons CLI complains on unexpected
 		// options
-		// Also so that Commons CLI can be excluded from the shaded JAR, as it is
-		// included in the bootstrap
 		if (Arrays.stream(args).map(str -> {
 			if (str == null) return "";
 			if (str.startsWith("--")) {

src/main/kotlin/link/infra/packwiz/installer/DevMain.kt

@@ -0,0 +1,5 @@
+package link.infra.packwiz.installer
+
+fun main(args: Array<String>) {
+	Main(args)
+}

src/main/kotlin/link/infra/packwiz/installer/DownloadTask.kt

@@ -6,18 +6,20 @@ import link.infra.packwiz.installer.metadata.SpaceSafeURI
 import link.infra.packwiz.installer.metadata.hash.Hash
 import link.infra.packwiz.installer.metadata.hash.HashUtils.getHash
 import link.infra.packwiz.installer.metadata.hash.HashUtils.getHasher
-import link.infra.packwiz.installer.ui.ExceptionDetails
-import link.infra.packwiz.installer.ui.IOptionDetails
-import okio.Buffer
-import okio.HashingSink
-import okio.buffer
+import link.infra.packwiz.installer.target.Side
+import link.infra.packwiz.installer.ui.data.ExceptionDetails
+import link.infra.packwiz.installer.ui.data.IOptionDetails
+import link.infra.packwiz.installer.util.Log
+import okio.*
+import okio.Path.Companion.toOkioPath
 import java.io.IOException
 import java.nio.file.Files
 import java.nio.file.Paths
 import java.nio.file.StandardCopyOption
 import java.util.*
+import kotlin.io.use
 
-internal class DownloadTask private constructor(val metadata: IndexFile.File, defaultFormat: String, private val downloadSide: UpdateManager.Options.Side) : IOptionDetails {
+internal class DownloadTask private constructor(val metadata: IndexFile.File, defaultFormat: String, private val downloadSide: Side) : IOptionDetails {
 	var cachedFile: ManifestFile.File? = null
 
 	private var err: Exception? = null
@@ -25,7 +27,7 @@ internal class DownloadTask private constructor(val metadata: IndexFile.File, de
 
 	fun failed() = err != null
 
-	private var alreadyUpToDate = false
+	var alreadyUpToDate = false
 	private var metadataRequired = true
 	private var invalidated = false
 	// If file is new or isOptional changed to true, the option needs to be presented again
@@ -122,27 +124,77 @@ internal class DownloadTask private constructor(val metadata: IndexFile.File, de
 		}
 	}
 
+	/**
+	 * Check if the file in the destination location is already valid
+	 * Must be done after metadata retrieval
+	 */
+	fun validateExistingFile(packFolder: String) {
+		if (!alreadyUpToDate) {
+			try {
+				// TODO: only do this for files that didn't exist before or have been modified since last full update?
+				val destPath = Paths.get(packFolder, metadata.destURI.toString())
+				FileSystem.SYSTEM.source(destPath.toOkioPath()).buffer().use { src ->
+					val hash: Hash
+					val fileHashFormat: String
+					val linkedFile = metadata.linkedFile
+
+					if (linkedFile != null) {
+						hash = linkedFile.hash
+						fileHashFormat = linkedFile.download!!.hashFormat!!
+					} else {
+						hash = metadata.getHashObj()
+						fileHashFormat = metadata.hashFormat!!
+					}
+
+					val fileSource = getHasher(fileHashFormat).getHashingSource(src)
+					fileSource.buffer().readAll(blackholeSink())
+					if (fileSource.hashIsEqual(hash)) {
+						alreadyUpToDate = true
+
+						// Update the manifest file
+						cachedFile = (cachedFile ?: ManifestFile.File()).also {
+							try {
+								it.hash = metadata.getHashObj()
+							} catch (e: Exception) {
+								err = e
+								return
+							}
+							it.isOptional = isOptional
+							it.cachedLocation = metadata.destURI.toString()
+							metadata.linkedFile?.let { linked ->
+								try {
+									it.linkedFileHash = linked.hash
+								} catch (e: Exception) {
+									err = e
+								}
+							}
+						}
+					}
+				}
+			} catch (e: IOException) {
+				// Ignore exceptions; if the file doesn't exist we'll be downloading it
+			}
+		}
+	}
+
 	fun download(packFolder: String, indexUri: SpaceSafeURI) {
 		if (err != null) return
 
-		// Ensure it is removed
+		// Ensure wrong-side or optional false files are removed
 		cachedFile?.let {
-			if (!it.optionValue || !correctSide()) {
-				if (it.cachedLocation == null) return
-
-				try {
-					Files.deleteIfExists(Paths.get(packFolder, it.cachedLocation))
-				} catch (e: IOException) {
-					// TODO: how much of a problem is this? use log4j/other log library to show warning?
-					e.printStackTrace()
+			if ((it.isOptional && !it.optionValue) || !correctSide()) {
+				if (it.cachedLocation != null) {
+					try {
+						Files.deleteIfExists(Paths.get(packFolder, it.cachedLocation))
+					} catch (e: IOException) {
+						Log.warn("Failed to delete file before downloading", e)
+					}
 				}
 				it.cachedLocation = null
 			}
 		}
 		if (alreadyUpToDate) return
 
-		// TODO: should I be validating JSON properly, or this fine!!!!!!!??
-		assert(metadata.destURI != null)
 		val destPath = Paths.get(packFolder, metadata.destURI.toString())
 
 		// Don't update files marked with preserve if they already exist on disk
@@ -152,6 +204,9 @@ internal class DownloadTask private constructor(val metadata: IndexFile.File, de
 			}
 		}
 
+		// TODO: if already exists and has correct hash, ignore?
+		// TODO: add .disabled support?
+
 		try {
 			val hash: Hash
 			val fileHashFormat: String
@@ -159,10 +214,10 @@ internal class DownloadTask private constructor(val metadata: IndexFile.File, de
 
 			if (linkedFile != null) {
 				hash = linkedFile.hash
-				fileHashFormat = Objects.requireNonNull(Objects.requireNonNull(linkedFile.download)!!.hashFormat)!!
+				fileHashFormat = linkedFile.download!!.hashFormat!!
 			} else {
 				hash = metadata.getHashObj()
-				fileHashFormat = Objects.requireNonNull(metadata.hashFormat)!!
+				fileHashFormat = metadata.hashFormat!!
 			}
 
 			val src = metadata.getSource(indexUri)
@@ -176,16 +231,23 @@ internal class DownloadTask private constructor(val metadata: IndexFile.File, de
 			}
 
 			if (fileSource.hashIsEqual(hash)) {
-				Files.createDirectories(destPath.parent)
+				// isDirectory follows symlinks, but createDirectories doesn't
+				try {
+					Files.createDirectories(destPath.parent)
+				} catch (e: java.nio.file.FileAlreadyExistsException) {
+					if (!Files.isDirectory(destPath.parent)) {
+						throw e
+					}
+				}
 				Files.copy(data.inputStream(), destPath, StandardCopyOption.REPLACE_EXISTING)
 				data.clear()
 			} else {
-				// TODO: no more PRINTLN!!!!!!!!!
+				// TODO: move println to something visible in the error window
 				println("Invalid hash for " + metadata.destURI.toString())
 				println("Calculated: " + fileSource.hash)
 				println("Expected:   $hash")
 				// Attempt to get the SHA256 hash
-				val sha256 = HashingSink.sha256(okio.blackholeSink())
+				val sha256 = HashingSink.sha256(blackholeSink())
 				data.readAll(sha256)
 				println("SHA256 hash value: " + sha256.hash)
 				err = Exception("Hash invalid!")
@@ -230,7 +292,7 @@ internal class DownloadTask private constructor(val metadata: IndexFile.File, de
 
 	companion object {
 		@JvmStatic
-		fun createTasksFromIndex(index: IndexFile, defaultFormat: String, downloadSide: UpdateManager.Options.Side): List<DownloadTask> {
+		fun createTasksFromIndex(index: IndexFile, defaultFormat: String, downloadSide: Side): MutableList<DownloadTask> {
 			val tasks = ArrayList<DownloadTask>()
 			for (file in Objects.requireNonNull(index.files)) {
 				tasks.add(DownloadTask(file, defaultFormat, downloadSide))

src/main/kotlin/link/infra/packwiz/installer/Main.kt

@@ -1,9 +1,12 @@
+@file:JvmName("Main")
+
 package link.infra.packwiz.installer
 
 import link.infra.packwiz.installer.metadata.SpaceSafeURI
-import link.infra.packwiz.installer.ui.CLIHandler
-import link.infra.packwiz.installer.ui.InputStateHandler
-import link.infra.packwiz.installer.ui.InstallWindow
+import link.infra.packwiz.installer.target.Side
+import link.infra.packwiz.installer.ui.cli.CLIHandler
+import link.infra.packwiz.installer.ui.gui.GUIHandler
+import link.infra.packwiz.installer.util.Log
 import org.apache.commons.cli.DefaultParser
 import org.apache.commons.cli.Options
 import org.apache.commons.cli.ParseException
@@ -16,6 +19,9 @@ import kotlin.system.exitProcess
 
 @Suppress("unused")
 class Main(args: Array<String>) {
+	// Don't attempt to start a GUI if we are headless
+	private var guiEnabled = !GraphicsEnvironment.isHeadless()
+
 	private fun startup(args: Array<String>) {
 		val options = Options()
 		addNonBootstrapOptions(options)
@@ -25,65 +31,65 @@ class Main(args: Array<String>) {
 		val cmd = try {
 			parser.parse(options, args)
 		} catch (e: ParseException) {
-			e.printStackTrace()
-			try {
-				UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName())
-			} catch (e1: Exception) {
-				// Ignore the exceptions, just continue using the ugly L&F
+			Log.fatal("Failed to parse command line arguments", e)
+			if (guiEnabled) {
+				EventQueue.invokeAndWait {
+					try {
+						UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName())
+					} catch (ignored: Exception) {
+						// Ignore the exceptions, just continue using the ugly L&F
+					}
+					JOptionPane.showMessageDialog(null, "Failed to parse command line arguments: $e",
+						"packwiz-installer", JOptionPane.ERROR_MESSAGE)
+				}
 			}
-			JOptionPane.showMessageDialog(null, e.message, "packwiz-installer", JOptionPane.ERROR_MESSAGE)
 			exitProcess(1)
 		}
 
-		// if "headless", GUI creation will fail anyway!
-		val ui = if (cmd.hasOption("no-gui") || GraphicsEnvironment.isHeadless()) {
-			CLIHandler()
-		} else InstallWindow()
+		if (guiEnabled && cmd.hasOption("no-gui")) {
+			guiEnabled = false
+		}
+
+		val ui = if (guiEnabled) GUIHandler() else CLIHandler()
 
 		val unparsedArgs = cmd.args
 		if (unparsedArgs.size > 1) {
-			ui.handleExceptionAndExit(RuntimeException("Too many arguments specified!"))
+			ui.showErrorAndExit("Too many arguments specified!")
 		} else if (unparsedArgs.isEmpty()) {
-			ui.handleExceptionAndExit(RuntimeException("URI to install from must be specified!"))
+			ui.showErrorAndExit("pack.toml URI to install from must be specified!")
 		}
 
-		cmd.getOptionValue("title")?.also {
-			ui.setTitle(it)
+		val title = cmd.getOptionValue("title")
+		if (title != null) {
+			ui.title = title
 		}
 
-		val inputStateHandler = InputStateHandler()
-		ui.show(inputStateHandler)
+		ui.show()
 
-		val uOptions = UpdateManager.Options().apply {
-			side = cmd.getOptionValue("side")?.let { UpdateManager.Options.Side.from(it) } ?: side
-			packFolder = cmd.getOptionValue("pack-folder") ?: packFolder
-			manifestFile = cmd.getOptionValue("meta-file") ?: manifestFile
-		}
-
-		try {
-			uOptions.downloadURI = SpaceSafeURI(unparsedArgs[0])
+		val uOptions = try {
+			UpdateManager.Options.construct(
+				downloadURI = SpaceSafeURI(unparsedArgs[0]),
+				side = cmd.getOptionValue("side")?.let((Side)::from),
+				packFolder = cmd.getOptionValue("pack-folder"),
+				manifestFile = cmd.getOptionValue("meta-file")
+			)
 		} catch (e: URISyntaxException) {
-			// TODO: better error message?
-			ui.handleExceptionAndExit(e)
+			ui.showErrorAndExit("Failed to read pack.toml URI", e)
 		}
 
 		// Start update process!
-		// TODO: start in SwingWorker?
 		try {
-			ui.executeManager {
-				try {
-					UpdateManager(uOptions, ui, inputStateHandler)
-				} catch (e: Exception) { // TODO: better error message?
-					ui.handleExceptionAndExit(e)
-				}
-			}
-		} catch (e: Exception) { // TODO: better error message?
-			ui.handleExceptionAndExit(e)
+			UpdateManager(uOptions, ui)
+		} catch (e: Exception) {
+			ui.showErrorAndExit("Update process failed", e)
 		}
+		println("Finished successfully!")
+		ui.dispose()
 	}
 
 	companion object {
 		// Called by packwiz-installer-bootstrap to set up the help command
+		@JvmStatic
 		fun addNonBootstrapOptions(options: Options) {
 			options.addOption("s", "side", true, "Side to install mods from (client/server, defaults to client)")
 			options.addOption(null, "title", true, "Title of the installer window")
@@ -92,6 +98,7 @@ class Main(args: Array<String>) {
 		}
 
 		// TODO: link these somehow so they're only defined once?
+		@JvmStatic
 		private fun addBootstrapOptions(options: Options) {
 			options.addOption(null, "bootstrap-update-url", true, "Github API URL for checking for updates")
 			options.addOption(null, "bootstrap-update-token", true, "Github API Access Token, for private repositories")
@@ -108,15 +115,17 @@ class Main(args: Array<String>) {
 		try {
 			startup(args)
 		} catch (e: Exception) {
-			e.printStackTrace()
-			EventQueue.invokeLater {
-				JOptionPane.showMessageDialog(null,
-						"A fatal error occurred: \n" + e.javaClass.canonicalName + ": " + e.message,
+			Log.fatal("Error from main", e)
+			if (guiEnabled) {
+				EventQueue.invokeLater {
+					JOptionPane.showMessageDialog(null,
+						"A fatal error occurred: \n$e",
 						"packwiz-installer", JOptionPane.ERROR_MESSAGE)
-				exitProcess(1)
+					exitProcess(1)
+				}
+				// In case the EventQueue is broken, exit after 1 minute
+				Thread.sleep(60 * 1000.toLong())
 			}
-			// In case the EventQueue is broken, exit after 1 minute
-			Thread.sleep(60 * 1000.toLong())
 			exitProcess(1)
 		}
 	}

src/main/kotlin/link/infra/packwiz/installer/UpdateManager.kt

@@ -3,38 +3,36 @@ package link.infra.packwiz.installer
 import com.google.gson.GsonBuilder
 import com.google.gson.JsonIOException
 import com.google.gson.JsonSyntaxException
-import com.google.gson.annotations.SerializedName
 import com.moandjiezana.toml.Toml
 import link.infra.packwiz.installer.DownloadTask.Companion.createTasksFromIndex
 import link.infra.packwiz.installer.metadata.IndexFile
 import link.infra.packwiz.installer.metadata.ManifestFile
 import link.infra.packwiz.installer.metadata.PackFile
 import link.infra.packwiz.installer.metadata.SpaceSafeURI
+import link.infra.packwiz.installer.metadata.curseforge.resolveCfMetadata
 import link.infra.packwiz.installer.metadata.hash.Hash
 import link.infra.packwiz.installer.metadata.hash.HashUtils.getHash
 import link.infra.packwiz.installer.metadata.hash.HashUtils.getHasher
 import link.infra.packwiz.installer.request.HandlerManager.getFileSource
 import link.infra.packwiz.installer.request.HandlerManager.getNewLoc
+import link.infra.packwiz.installer.target.Side
 import link.infra.packwiz.installer.ui.IUserInterface
 import link.infra.packwiz.installer.ui.IUserInterface.CancellationResult
 import link.infra.packwiz.installer.ui.IUserInterface.ExceptionListResult
-import link.infra.packwiz.installer.ui.InputStateHandler
-import link.infra.packwiz.installer.ui.InstallProgress
+import link.infra.packwiz.installer.ui.data.InstallProgress
+import link.infra.packwiz.installer.util.Log
+import link.infra.packwiz.installer.util.ifletOrErr
 import okio.buffer
-import java.io.FileNotFoundException
-import java.io.FileReader
-import java.io.FileWriter
-import java.io.IOException
+import java.io.*
 import java.nio.file.Files
 import java.nio.file.Paths
-import java.util.*
 import java.util.concurrent.CompletionService
 import java.util.concurrent.ExecutionException
 import java.util.concurrent.ExecutorCompletionService
 import java.util.concurrent.Executors
 import kotlin.system.exitProcess
 
-class UpdateManager internal constructor(private val opts: Options, val ui: IUserInterface, private val stateHandler: InputStateHandler) {
+class UpdateManager internal constructor(private val opts: Options, val ui: IUserInterface) {
 	private var cancelled = false
 	private var cancelledStartGame = false
 	private var errorsOccurred = false
@@ -44,61 +42,17 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 	}
 
 	data class Options(
-			var downloadURI: SpaceSafeURI? = null,
-			var manifestFile: String = "packwiz.json", // TODO: make configurable
-			var packFolder: String = ".",
-			var side: Side = Side.CLIENT
+		val downloadURI: SpaceSafeURI,
+		val manifestFile: String,
+		val packFolder: String,
+		val side: Side
 	) {
-		enum class Side {
-			@SerializedName("client")
-			CLIENT("client"),
-			@SerializedName("server")
-			SERVER("server"),
-			@SerializedName("both")
-			@Suppress("unused")
-			BOTH("both", arrayOf(CLIENT, SERVER));
-
-			private val sideName: String
-			private val depSides: Array<Side>?
-
-			constructor(sideName: String) {
-				this.sideName = sideName.toLowerCase()
-				depSides = null
-			}
-
-			constructor(sideName: String, depSides: Array<Side>) {
-				this.sideName = sideName.toLowerCase()
-				this.depSides = depSides
-			}
-
-			override fun toString() = sideName
-
-			fun hasSide(tSide: Side): Boolean {
-				if (this == tSide) {
-					return true
-				}
-				if (depSides != null) {
-					for (depSide in depSides) {
-						if (depSide == tSide) {
-							return true
-						}
-					}
-				}
-				return false
-			}
-
-			companion object {
-				fun from(name: String): Side? {
-					val lowerName = name.toLowerCase()
-					for (side in values()) {
-						if (side.sideName == lowerName) {
-							return side
-						}
-					}
-					return null
-				}
-			}
+		// Horrible workaround for default params not working cleanly with nullable values
+		companion object {
+			fun construct(downloadURI: SpaceSafeURI, manifestFile: String?, packFolder: String?, side: Side?) =
+				Options(downloadURI, manifestFile ?: "packwiz.json", packFolder ?: ".", side ?: Side.CLIENT)
 		}
+
 	}
 
 	private fun start() {
@@ -110,40 +64,35 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 			gson.fromJson(FileReader(Paths.get(opts.packFolder, opts.manifestFile).toString()),
 					ManifestFile::class.java)
 		} catch (e: FileNotFoundException) {
+			ui.firstInstall = true
 			ManifestFile()
 		} catch (e: JsonSyntaxException) {
-			ui.handleExceptionAndExit(e)
-			return
+			ui.showErrorAndExit("Invalid local manifest file, try deleting ${opts.manifestFile}", e)
 		} catch (e: JsonIOException) {
-			ui.handleExceptionAndExit(e)
-			return
+			ui.showErrorAndExit("Failed to read local manifest file, try deleting ${opts.manifestFile}", e)
 		}
 
-		if (stateHandler.cancelButton) {
+		if (ui.cancelButtonPressed) {
 			showCancellationDialog()
 			handleCancellation()
 		}
 
 		ui.submitProgress(InstallProgress("Loading pack file..."))
 		val packFileSource = try {
-			Objects.requireNonNull(opts.downloadURI)
-			val src = getFileSource(opts.downloadURI!!)
+			val src = getFileSource(opts.downloadURI)
 			getHasher("sha256").getHashingSource(src)
 		} catch (e: Exception) {
-			// TODO: run cancellation window?
-			ui.handleExceptionAndExit(e)
-			return
+			ui.showErrorAndExit("Failed to download pack.toml", e)
 		}
 		val pf = packFileSource.buffer().use {
 			try {
-				Toml().read(it.inputStream()).to(PackFile::class.java)
+				Toml().read(InputStreamReader(it.inputStream(), "UTF-8")).to(PackFile::class.java)
 			} catch (e: IllegalStateException) {
-				ui.handleExceptionAndExit(e)
-				return
+				ui.showErrorAndExit("Failed to parse pack.toml", e)
 			}
 		}
 
-		if (stateHandler.cancelButton) {
+		if (ui.cancelButtonPressed) {
 			showCancellationDialog()
 			handleCancellation()
 		}
@@ -171,36 +120,45 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 				}
 			}
 			if (invalid) {
-				println("File $fileUri invalidated, marked for redownloading")
+				Log.info("File $fileUri invalidated, marked for redownloading")
 				invalidatedUris.add(fileUri)
 			}
 		}
 
 		if (manifest.packFileHash?.let { packFileSource.hashIsEqual(it) } == true && invalidatedUris.isEmpty()) {
-			println("Modpack is already up to date!")
 			// todo: --force?
-			if (!stateHandler.optionsButton) {
+			ui.submitProgress(InstallProgress("Modpack is already up to date!", 1, 1))
+			if (manifest.cachedFiles.any { it.value.isOptional }) {
+				ui.awaitOptionalButton(false)
+			}
+			if (!ui.optionsButtonPressed) {
 				return
 			}
 		}
 
-		println("Modpack name: " + pf.name)
+		Log.info("Modpack name: ${pf.name}")
 
-		if (stateHandler.cancelButton) {
+		if (ui.cancelButtonPressed) {
 			showCancellationDialog()
 			handleCancellation()
 		}
 		try {
-			// This is badly written, I'll probably heavily refactor it at some point
-			// The port to Kotlin made this REALLY messy!!!!
-			getNewLoc(opts.downloadURI, Objects.requireNonNull(pf.index)!!.file)?.let {
-				pf.index!!.hashFormat?.let { it1 ->
-					processIndex(it,
-							getHash(Objects.requireNonNull(pf.index!!.hashFormat)!!, Objects.requireNonNull(pf.index!!.hash)!!), it1, manifest, invalidatedUris)
+			// TODO: switch to OkHttp for better redirect handling
+			ui.ifletOrErr(pf.index, "No index file found, or the pack file is empty; note that Java doesn't automatically follow redirects from HTTP to HTTPS (and may cause this error)") { index ->
+				ui.ifletOrErr(index.hashFormat, index.hash, "Pack has no hash or hashFormat for index") { hashFormat, hash ->
+					ui.ifletOrErr(getNewLoc(opts.downloadURI, index.file), "Pack has invalid index file: " + index.file) { newLoc ->
+						processIndex(
+							newLoc,
+							getHash(hashFormat, hash),
+							hashFormat,
+							manifest,
+							invalidatedUris
+						)
+					}
 				}
 			}
 		} catch (e1: Exception) {
-			ui.handleExceptionAndExit(e1)
+			ui.showErrorAndExit("Failed to process index file", e1)
 		}
 
 		handleCancellation()
@@ -219,8 +177,7 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 		try {
 			FileWriter(Paths.get(opts.packFolder, opts.manifestFile).toString()).use { writer -> gson.toJson(manifest, writer) }
 		} catch (e: IOException) {
-			// TODO: add message?
-			ui.handleException(e)
+			ui.showErrorAndExit("Failed to save local manifest file", e)
 		}
 	}
 
@@ -230,8 +187,15 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 
 	private fun processIndex(indexUri: SpaceSafeURI, indexHash: Hash, hashFormat: String, manifest: ManifestFile, invalidatedUris: List<SpaceSafeURI>) {
 		if (manifest.indexFileHash == indexHash && invalidatedUris.isEmpty()) {
-			println("Modpack files are already up to date!")
-			if (!stateHandler.optionsButton) {
+			ui.submitProgress(InstallProgress("Modpack files are already up to date!", 1, 1))
+			if (manifest.cachedFiles.any { it.value.isOptional }) {
+				ui.awaitOptionalButton(false)
+			}
+			if (!ui.optionsButtonPressed) {
+				return
+			}
+			if (ui.cancelButtonPressed) {
+				showCancellationDialog()
 				return
 			}
 		}
@@ -241,22 +205,19 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 			val src = getFileSource(indexUri)
 			getHasher(hashFormat).getHashingSource(src)
 		} catch (e: Exception) {
-			// TODO: run cancellation window?
-			ui.handleExceptionAndExit(e)
-			return
+			ui.showErrorAndExit("Failed to download index file", e)
 		}
+
 		val indexFile = try {
-			Toml().read(indexFileSource.buffer().inputStream()).to(IndexFile::class.java)
+			Toml().read(InputStreamReader(indexFileSource.buffer().inputStream(), "UTF-8")).to(IndexFile::class.java)
 		} catch (e: IllegalStateException) {
-			ui.handleExceptionAndExit(e)
-			return
+			ui.showErrorAndExit("Failed to parse index file", e)
 		}
 		if (!indexFileSource.hashIsEqual(indexHash)) {
-			// TODO: throw exception
-			println("I was meant to put an error message here but I'll do that later")
-			return
+			ui.showErrorAndExit("Your index file hash is invalid! The pack developer should packwiz refresh on the pack again")
 		}
-		if (stateHandler.cancelButton) {
+
+		if (ui.cancelButtonPressed) {
 			showCancellationDialog()
 			return
 		}
@@ -273,8 +234,7 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 					try {
 						Files.deleteIfExists(Paths.get(opts.packFolder, file.cachedLocation))
 					} catch (e: IOException) {
-						// TODO: should this be shown to the user in some way?
-						e.printStackTrace()
+						Log.warn("Failed to delete optional disabled file", e)
 					}
 					// Set to null, as it doesn't exist anymore
 					file.cachedLocation = null
@@ -284,8 +244,8 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 					if (!alreadyDeleted) {
 						try {
 							Files.deleteIfExists(Paths.get(opts.packFolder, file.cachedLocation))
-						} catch (e: IOException) { // TODO: should this be shown to the user in some way?
-							e.printStackTrace()
+						} catch (e: IOException) {
+							Log.warn("Failed to delete file removed from index", e)
 						}
 					}
 					it.remove()
@@ -293,7 +253,7 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 			}
 		}
 
-		if (stateHandler.cancelButton) {
+		if (ui.cancelButtonPressed) {
 			showCancellationDialog()
 			return
 		}
@@ -301,14 +261,14 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 
 		// TODO: progress bar?
 		if (indexFile.files.isEmpty()) {
-			println("Warning: Index is empty!")
+			Log.warn("Index is empty!")
 		}
 		val tasks = createTasksFromIndex(indexFile, indexFile.hashFormat, opts.side)
 		// If the side changes, invalidate EVERYTHING just in case
 		// Might not be needed, but done just to be safe
 		val invalidateAll = opts.side != manifest.cachedSide
 		if (invalidateAll) {
-			println("Side changed, invalidating all mods")
+			Log.info("Side changed, invalidating all mods")
 		}
 		tasks.forEach{ f ->
 			// TODO: should linkedfile be checked as well? should this be done in the download section?
@@ -324,7 +284,7 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 			f.updateFromCache(file)
 		}
 
-		if (stateHandler.cancelButton) {
+		if (ui.cancelButtonPressed) {
 			showCancellationDialog()
 			return
 		}
@@ -335,17 +295,7 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 		val failedTaskDetails = tasks.asSequence().map(DownloadTask::exceptionDetails).filterNotNull().toList()
 		if (failedTaskDetails.isNotEmpty()) {
 			errorsOccurred = true
-			val exceptionListResult: ExceptionListResult
-			exceptionListResult = try {
-				ui.showExceptions(failedTaskDetails, tasks.size, true).get()
-			} catch (e: InterruptedException) { // Interrupted means cancelled???
-				ui.handleExceptionAndExit(e)
-				return
-			} catch (e: ExecutionException) {
-				ui.handleExceptionAndExit(e)
-				return
-			}
-			when (exceptionListResult) {
+			when (ui.showExceptions(failedTaskDetails, tasks.size, true)) {
 				ExceptionListResult.CONTINUE -> {}
 				ExceptionListResult.CANCEL -> {
 					cancelled = true
@@ -358,32 +308,44 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 			}
 		}
 
-		if (stateHandler.cancelButton) {
+		if (ui.cancelButtonPressed) {
 			showCancellationDialog()
 			return
 		}
 
 		// TODO: task failed function?
-		val nonFailedFirstTasks = tasks.filter { t -> !t.failed() }.toList()
-		val optionTasks = nonFailedFirstTasks.filter(DownloadTask::correctSide).filter(DownloadTask::isOptional).toList()
-		// If options changed, present all options again
-		if (stateHandler.optionsButton || optionTasks.any(DownloadTask::isNewOptional)) {
-			// new ArrayList is required so it's an IOptionDetails rather than a DownloadTask list
-			val cancelledResult = ui.showOptions(ArrayList(optionTasks))
-			try {
-				if (cancelledResult.get()) {
-					cancelled = true
-					// TODO: Should the UI be closed somehow??
+		tasks.removeAll { it.failed() }
+		val optionTasks = tasks.filter(DownloadTask::correctSide).filter(DownloadTask::isOptional).toList()
+		val optionsChanged = optionTasks.any(DownloadTask::isNewOptional)
+		if (optionTasks.isNotEmpty() && !optionsChanged) {
+			if (!ui.optionsButtonPressed) {
+				// TODO: this is so ugly
+				ui.submitProgress(InstallProgress("Reconfigure optional mods?", 0,1))
+				ui.awaitOptionalButton(true)
+				if (ui.cancelButtonPressed) {
+					showCancellationDialog()
 					return
 				}
-			} catch (e: InterruptedException) {
-				// Interrupted means cancelled???
-				ui.handleExceptionAndExit(e)
-			} catch (e: ExecutionException) {
-				ui.handleExceptionAndExit(e)
 			}
 		}
-		ui.disableOptionsButton()
+		// If options changed, present all options again
+		if (ui.optionsButtonPressed || optionsChanged) {
+			// new ArrayList is required so it's an IOptionDetails rather than a DownloadTask list
+			if (ui.showOptions(ArrayList(optionTasks))) {
+				cancelled = true
+				handleCancellation()
+			}
+		}
+		// TODO: keep this enabled? then apply changes after download process?
+		ui.disableOptionsButton(optionTasks.isNotEmpty())
+
+		while (true) {
+			when (validateAndResolve(tasks)) {
+				ResolveResult.RETRY -> {}
+				ResolveResult.QUIT -> return
+				ResolveResult.SUCCESS -> break
+			}
+		}
 
 		// TODO: different thread pool type?
 		val threadPool = Executors.newFixedThreadPool(10)
@@ -395,18 +357,15 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 			}
 		}
 		for (i in tasks.indices) {
-			var task: DownloadTask?
-			task = try {
+			val task: DownloadTask = try {
 				completionService.take().get()
 			} catch (e: InterruptedException) {
-				ui.handleException(e)
-				null
+				ui.showErrorAndExit("Interrupted when consuming download tasks", e)
 			} catch (e: ExecutionException) {
-				ui.handleException(e)
-				null
+				ui.showErrorAndExit("Failed to execute download task", e)
 			}
 			// Update manifest - If there were no errors cachedFile has already been modified in place (good old pass by reference)
-			task?.cachedFile?.let { file ->
+			task.cachedFile?.let { file ->
 				if (task.failed()) {
 					val oldFile = file.revert
 					if (oldFile != null) {
@@ -417,21 +376,15 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 				}
 			}
 
-			var progress: String
-			if (task != null) {
-				val exDetails = task.exceptionDetails
-				if (exDetails != null) {
-					progress = "Failed to download ${exDetails.name}: ${exDetails.exception.message}"
-					exDetails.exception.printStackTrace()
-				} else {
-					progress = "Downloaded ${task.name}"
-				}
+			val exDetails = task.exceptionDetails
+			val progress = if (exDetails != null) {
+				"Failed to download ${exDetails.name}: ${exDetails.exception.message}"
 			} else {
-				progress = "Failed to download, unknown reason"
+				"Downloaded ${task.name}"
 			}
 			ui.submitProgress(InstallProgress(progress, i + 1, tasks.size))
 
-			if (stateHandler.cancelButton) { // Stop all tasks, don't launch the game (it's in an invalid state!)
+			if (ui.cancelButtonPressed) { // Stop all tasks, don't launch the game (it's in an invalid state!)
 				threadPool.shutdown()
 				cancelled = true
 				return
@@ -441,21 +394,10 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 		// Shut down the thread pool when the update is done
 		threadPool.shutdown()
 
-		val failedTasks2ElectricBoogaloo = nonFailedFirstTasks.asSequence().map(DownloadTask::exceptionDetails).filterNotNull().toList()
+		val failedTasks2ElectricBoogaloo = tasks.asSequence().map(DownloadTask::exceptionDetails).filterNotNull().toList()
 		if (failedTasks2ElectricBoogaloo.isNotEmpty()) {
 			errorsOccurred = true
-			val exceptionListResult: ExceptionListResult
-			exceptionListResult = try {
-				ui.showExceptions(failedTasks2ElectricBoogaloo, tasks.size, false).get()
-			} catch (e: InterruptedException) {
-				// Interrupted means cancelled???
-				ui.handleExceptionAndExit(e)
-				return
-			} catch (e: ExecutionException) {
-				ui.handleExceptionAndExit(e)
-				return
-			}
-			when (exceptionListResult) {
+			when (ui.showExceptions(failedTasks2ElectricBoogaloo, tasks.size, false)) {
 				ExceptionListResult.CONTINUE -> {}
 				ExceptionListResult.CANCEL -> cancelled = true
 				ExceptionListResult.IGNORE -> cancelledStartGame = true
@@ -463,24 +405,57 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 		}
 	}
 
-	private fun showCancellationDialog() {
-		val cancellationResult: CancellationResult
-		cancellationResult = try {
-			ui.showCancellationDialog().get()
-		} catch (e: InterruptedException) {
-			// Interrupted means cancelled???
-			ui.handleExceptionAndExit(e)
-			return
-		} catch (e: ExecutionException) {
-			ui.handleExceptionAndExit(e)
-			return
+	enum class ResolveResult {
+		RETRY,
+		QUIT,
+		SUCCESS;
+	}
+
+	private fun validateAndResolve(nonFailedFirstTasks: List<DownloadTask>): ResolveResult {
+		ui.submitProgress(InstallProgress("Validating existing files..."))
+
+		// Validate existing files
+		for (downloadTask in nonFailedFirstTasks.filter(DownloadTask::correctSide)) {
+			downloadTask.validateExistingFile(opts.packFolder)
 		}
-		when (cancellationResult) {
+
+		// Resolve CurseForge metadata
+		val cfFiles = nonFailedFirstTasks.asSequence().filter { !it.alreadyUpToDate }
+			.filter(DownloadTask::correctSide)
+			.map { it.metadata }
+			.filter { it.linkedFile != null }
+			.filter { it.linkedFile?.download?.mode == "metadata:curseforge" }.toList()
+		if (cfFiles.isNotEmpty()) {
+			ui.submitProgress(InstallProgress("Resolving CurseForge metadata..."))
+			val resolveFailures = resolveCfMetadata(cfFiles)
+			if (resolveFailures.isNotEmpty()) {
+				errorsOccurred = true
+				return when (ui.showExceptions(resolveFailures, cfFiles.size, true)) {
+					ExceptionListResult.CONTINUE -> {
+						ResolveResult.RETRY
+					}
+					ExceptionListResult.CANCEL -> {
+						cancelled = true
+						ResolveResult.QUIT
+					}
+					ExceptionListResult.IGNORE -> {
+						cancelledStartGame = true
+						ResolveResult.QUIT
+					}
+				}
+			}
+		}
+		return ResolveResult.SUCCESS
+	}
+
+	private fun showCancellationDialog() {
+		when (ui.showCancellationDialog()) {
 			CancellationResult.QUIT -> cancelled = true
 			CancellationResult.CONTINUE -> cancelledStartGame = true
 		}
 	}
 
+	// TODO: move to UI?
 	private fun handleCancellation() {
 		if (cancelled) {
 			println("Update cancelled by user!")
@@ -490,4 +465,5 @@ class UpdateManager internal constructor(private val opts: Options, val ui: IUse
 			exitProcess(0)
 		}
 	}
+
 }

src/main/kotlin/link/infra/packwiz/installer/metadata/IndexFile.kt

@@ -9,6 +9,7 @@ import link.infra.packwiz.installer.request.HandlerManager.getFileSource
 import link.infra.packwiz.installer.request.HandlerManager.getNewLoc
 import okio.Source
 import okio.buffer
+import java.io.InputStreamReader
 import java.nio.file.Paths
 
 class IndexFile {
@@ -43,7 +44,7 @@ class IndexFile {
 			linkedFileURI = getNewLoc(indexUri, file)
 			val src = getFileSource(linkedFileURI!!)
 			val fileStream = getHasher(hashFormat!!).getHashingSource(src)
-			linkedFile = Toml().read(fileStream.buffer().inputStream()).to(ModFile::class.java)
+			linkedFile = Toml().read(InputStreamReader(fileStream.buffer().inputStream(), "UTF-8")).to(ModFile::class.java)
 			if (!fileStream.hashIsEqual(fileHash)) {
 				throw Exception("Invalid mod file hash")
 			}
@@ -78,9 +79,9 @@ class IndexFile {
 			get() {
 				if (metafile) {
 					return linkedFile?.name ?: linkedFile?.filename ?:
-					file?.run { Paths.get(path).fileName.toString() } ?: "Invalid file"
+					file?.run { Paths.get(path ?: return "Invalid file").fileName.toString() } ?: "Invalid file"
 				}
-				return file?.run { Paths.get(path).fileName.toString() } ?: "Invalid file"
+				return file?.run { Paths.get(path ?: return "Invalid file").fileName.toString() } ?: "Invalid file"
 			}
 
 		// TODO: URIs are bad

src/main/kotlin/link/infra/packwiz/installer/metadata/ManifestFile.kt

@@ -1,15 +1,15 @@
 package link.infra.packwiz.installer.metadata
 
 import com.google.gson.annotations.JsonAdapter
-import link.infra.packwiz.installer.UpdateManager
 import link.infra.packwiz.installer.metadata.hash.Hash
+import link.infra.packwiz.installer.target.Side
 
 class ManifestFile {
 	var packFileHash: Hash? = null
 	var indexFileHash: Hash? = null
 	var cachedFiles: MutableMap<SpaceSafeURI, File> = HashMap()
 	// If the side changes, EVERYTHING invalidates. FUN!!!
-	var cachedSide = UpdateManager.Options.Side.CLIENT
+	var cachedSide = Side.CLIENT
 
 	// TODO: switch to Kotlin-friendly JSON/TOML libs?
 	class File {

src/main/kotlin/link/infra/packwiz/installer/metadata/ModFile.kt

@@ -1,17 +1,20 @@
 package link.infra.packwiz.installer.metadata
 
+import com.google.gson.annotations.JsonAdapter
 import com.google.gson.annotations.SerializedName
-import link.infra.packwiz.installer.UpdateManager
+import link.infra.packwiz.installer.metadata.curseforge.UpdateData
+import link.infra.packwiz.installer.metadata.curseforge.UpdateDeserializer
 import link.infra.packwiz.installer.metadata.hash.Hash
 import link.infra.packwiz.installer.metadata.hash.HashUtils.getHash
 import link.infra.packwiz.installer.request.HandlerManager.getFileSource
 import link.infra.packwiz.installer.request.HandlerManager.getNewLoc
+import link.infra.packwiz.installer.target.Side
 import okio.Source
 
 class ModFile {
 	var name: String? = null
 	var filename: String? = null
-	var side: UpdateManager.Options.Side? = null
+	var side: Side? = null
 	var download: Download? = null
 
 	class Download {
@@ -19,11 +22,16 @@ class ModFile {
 		@SerializedName("hash-format")
 		var hashFormat: String? = null
 		var hash: String? = null
+		var mode: String? = null
 	}
 
-	var update: Map<String, Any>? = null
+	@JsonAdapter(UpdateDeserializer::class)
+	var update: Map<String, UpdateData>? = null
 	var option: Option? = null
 
+	@Transient
+	val resolvedUpdateData = mutableMapOf<String, SpaceSafeURI>()
+
 	class Option {
 		var optional = false
 		var description: String? = null
@@ -34,11 +42,20 @@ class ModFile {
 	@Throws(Exception::class)
 	fun getSource(baseLoc: SpaceSafeURI?): Source {
 		download?.let {
-			if (it.url == null) {
-				throw Exception("Metadata file doesn't have a download URI")
+			if (it.mode == null || it.mode == "" || it.mode == "url") {
+				if (it.url == null) {
+					throw Exception("Metadata file doesn't have a download URI")
+				}
+				val newLoc = getNewLoc(baseLoc, it.url) ?: throw Exception("Metadata file URI is invalid")
+				return getFileSource(newLoc)
+			} else if (it.mode == "metadata:curseforge") {
+				if (!resolvedUpdateData.contains("curseforge")) {
+					throw Exception("Metadata file specifies CurseForge mode, but is missing metadata")
+				}
+				return getFileSource(resolvedUpdateData["curseforge"]!!)
+			} else {
+				throw Exception("Unsupported download mode " + it.mode)
 			}
-			val newLoc = getNewLoc(baseLoc, it.url) ?: throw Exception("Metadata file URI is invalid")
-			return getFileSource(newLoc)
 		} ?: throw Exception("Metadata file doesn't have download")
 	}
 

src/main/kotlin/link/infra/packwiz/installer/metadata/PackFile.kt

@@ -14,6 +14,4 @@ class PackFile {
 	}
 
 	var versions: Map<String, String>? = null
-	var client: Map<String, Any>? = null
-	var server: Map<String, Any>? = null
 }

src/main/kotlin/link/infra/packwiz/installer/metadata/SpaceSafeURI.kt

@@ -32,7 +32,7 @@ class SpaceSafeURI : Comparable<SpaceSafeURI>, Serializable {
 		)
 	}
 
-	val path: String get() = u.path.replace("%20", " ")
+	val path: String? get() = u.path?.replace("%20", " ")
 
 	override fun toString(): String = u.toString().replace("%20", " ")
 
@@ -52,9 +52,9 @@ class SpaceSafeURI : Comparable<SpaceSafeURI>, Serializable {
 
 	override fun compareTo(other: SpaceSafeURI): Int = u.compareTo(other.u)
 
-	val scheme: String get() = u.scheme
-	val authority: String get() = u.authority
-	val host: String get() = u.host
+	val scheme: String? get() = u.scheme
+	val authority: String? get() = u.authority
+	val host: String? get() = u.host
 
 	@Throws(MalformedURLException::class)
 	fun toURL(): URL = u.toURL()

src/main/kotlin/link/infra/packwiz/installer/metadata/curseforge/CurseForgeSourcer.kt

@@ -0,0 +1,132 @@
+package link.infra.packwiz.installer.metadata.curseforge
+
+import com.google.gson.Gson
+import com.google.gson.JsonIOException
+import com.google.gson.JsonSyntaxException
+import link.infra.packwiz.installer.metadata.IndexFile
+import link.infra.packwiz.installer.metadata.SpaceSafeURI
+import link.infra.packwiz.installer.target.ClientHolder
+import link.infra.packwiz.installer.ui.data.ExceptionDetails
+import okhttp3.MediaType.Companion.toMediaType
+import okhttp3.Request
+import okhttp3.RequestBody.Companion.toRequestBody
+import okhttp3.internal.closeQuietly
+import okio.ByteString.Companion.decodeBase64
+import java.nio.charset.StandardCharsets
+
+private class GetFilesRequest(val fileIds: List<Int>)
+private class GetModsRequest(val modIds: List<Int>)
+
+private class GetFilesResponse {
+	class CfFile {
+		var id = 0
+		var modId = 0
+		var downloadUrl: SpaceSafeURI? = null
+	}
+	val data = mutableListOf<CfFile>()
+}
+
+private class GetModsResponse {
+	class CfMod {
+		var id = 0
+		var name = ""
+		var links: CfLinks? = null
+	}
+	class CfLinks {
+		var websiteUrl = ""
+	}
+	val data = mutableListOf<CfMod>()
+}
+
+private const val APIServer = "api.curseforge.com"
+// If you fork/derive from packwiz, I request that you obtain your own API key.
+private val APIKey = "JDJhJDEwJHNBWVhqblU1N0EzSmpzcmJYM3JVdk92UWk2NHBLS3BnQ2VpbGc1TUM1UGNKL0RYTmlGWWxh".decodeBase64()!!
+	.string(StandardCharsets.UTF_8)
+
+private val clientHolder = ClientHolder()
+
+// TODO: switch to PackwizPath stuff and OkHttp in old code
+
+@Throws(JsonSyntaxException::class, JsonIOException::class)
+fun resolveCfMetadata(mods: List<IndexFile.File>): List<ExceptionDetails> {
+	val failures = mutableListOf<ExceptionDetails>()
+	val fileIdMap = mutableMapOf<Int, IndexFile.File>()
+
+	for (mod in mods) {
+		if (mod.linkedFile!!.update == null) {
+			failures.add(ExceptionDetails(mod.linkedFile!!.name ?: mod.linkedFile!!.filename!!, Exception("Failed to resolve CurseForge metadata: no update section")))
+			continue
+		}
+		if (!mod.linkedFile!!.update!!.contains("curseforge")) {
+			failures.add(ExceptionDetails(mod.linkedFile!!.name ?: mod.linkedFile!!.filename!!, Exception("Failed to resolve CurseForge metadata: no CurseForge update section")))
+			continue
+		}
+		fileIdMap[(mod.linkedFile!!.update!!["curseforge"] as CurseForgeUpdateData).fileId] = mod
+	}
+
+	val reqData = GetFilesRequest(fileIdMap.keys.toList())
+	val req = Request.Builder()
+		.url("https://${APIServer}/v1/mods/files")
+		.header("Accept", "application/json")
+		.header("User-Agent", "packwiz-installer")
+		.header("X-API-Key", APIKey)
+		.post(Gson().toJson(reqData, GetFilesRequest::class.java).toRequestBody("application/json".toMediaType()))
+		.build()
+	val res = clientHolder.okHttpClient.newCall(req).execute()
+	if (!res.isSuccessful || res.body == null) {
+		res.closeQuietly()
+		failures.add(ExceptionDetails("Other", Exception("Failed to resolve CurseForge metadata for file data: error code ${res.code}")))
+		return failures
+	}
+
+	val resData = Gson().fromJson(res.body!!.charStream(), GetFilesResponse::class.java)
+	res.closeQuietly()
+
+	val manualDownloadMods = mutableMapOf<Int, Pair<IndexFile.File, Int>>()
+	for (file in resData.data) {
+		if (!fileIdMap.contains(file.id)) {
+			failures.add(ExceptionDetails(file.id.toString(),
+				Exception("Failed to find file from result: ID ${file.id}, Project ID ${file.modId}")))
+			continue
+		}
+		if (file.downloadUrl == null) {
+			manualDownloadMods[file.modId] = Pair(fileIdMap[file.id]!!, file.id)
+			continue
+		}
+		fileIdMap[file.id]!!.linkedFile!!.resolvedUpdateData["curseforge"] = file.downloadUrl!!
+	}
+
+	if (manualDownloadMods.isNotEmpty()) {
+		val reqModsData = GetModsRequest(manualDownloadMods.keys.toList())
+		val reqMods = Request.Builder()
+			.url("https://${APIServer}/v1/mods")
+			.header("Accept", "application/json")
+			.header("User-Agent", "packwiz-installer")
+			.header("X-API-Key", APIKey)
+			.post(Gson().toJson(reqModsData, GetModsRequest::class.java).toRequestBody("application/json".toMediaType()))
+			.build()
+		val resMods = clientHolder.okHttpClient.newCall(reqMods).execute()
+		if (!resMods.isSuccessful || resMods.body == null) {
+			resMods.closeQuietly()
+			failures.add(ExceptionDetails("Other", Exception("Failed to resolve CurseForge metadata for mod data: error code ${resMods.code}")))
+			return failures
+		}
+
+		val resModsData = Gson().fromJson(resMods.body!!.charStream(), GetModsResponse::class.java)
+		resMods.closeQuietly()
+
+		for (mod in resModsData.data) {
+			if (!manualDownloadMods.contains(mod.id)) {
+				failures.add(ExceptionDetails(mod.name,
+					Exception("Failed to find project from result: ID ${mod.id}")))
+				continue
+			}
+
+			val modFile = manualDownloadMods[mod.id]!!
+			failures.add(ExceptionDetails(mod.name, Exception("This mod is excluded from the CurseForge API and must be downloaded manually.\n" +
+				"Please go to ${mod.links?.websiteUrl}/files/${modFile.second} and save this file to ${modFile.first.destURI}")))
+		}
+	}
+
+	return failures
+}

src/main/kotlin/link/infra/packwiz/installer/metadata/curseforge/CurseForgeUpdateData.kt

@@ -0,0 +1,10 @@
+package link.infra.packwiz.installer.metadata.curseforge
+
+import com.google.gson.annotations.SerializedName
+
+class CurseForgeUpdateData: UpdateData {
+	@SerializedName("file-id")
+	var fileId = 0
+	@SerializedName("project-id")
+	var projectId = 0
+}

src/main/kotlin/link/infra/packwiz/installer/metadata/curseforge/UpdateData.kt

@@ -0,0 +1,3 @@
+package link.infra.packwiz.installer.metadata.curseforge
+
+interface UpdateData

src/main/kotlin/link/infra/packwiz/installer/metadata/curseforge/UpdateDeserializer.kt

@@ -0,0 +1,22 @@
+package link.infra.packwiz.installer.metadata.curseforge
+
+import com.google.gson.JsonDeserializationContext
+import com.google.gson.JsonDeserializer
+import com.google.gson.JsonElement
+import java.lang.reflect.Type
+
+class UpdateDeserializer: JsonDeserializer<Map<String, UpdateData>> {
+	override fun deserialize(
+		json: JsonElement?,
+		typeOfT: Type?,
+		context: JsonDeserializationContext?
+	): Map<String, UpdateData> {
+		val out = mutableMapOf<String, UpdateData>()
+		for ((k, v) in json!!.asJsonObject.entrySet()) {
+			if (k == "curseforge") {
+				out[k] = context!!.deserialize(v, CurseForgeUpdateData::class.java)
+			}
+		}
+		return out
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/metadata/hash/HashUtils.kt

@@ -4,7 +4,8 @@ object HashUtils {
 	private val hashTypeConversion: Map<String, IHasher> = mapOf(
 			"sha256" to HashingSourceHasher("sha256"),
 			"sha512" to HashingSourceHasher("sha512"),
-			"murmur2" to Murmur2Hasher()
+			"murmur2" to Murmur2Hasher(),
+			"sha1" to HashingSourceHasher("sha1")
 	)
 
 	@JvmStatic

src/main/kotlin/link/infra/packwiz/installer/metadata/hash/HashingSourceHasher.kt

@@ -5,7 +5,7 @@ import okio.Source
 
 class HashingSourceHasher internal constructor(private val type: String) : IHasher {
 	// i love naming things
-	private inner class HashingSourceGeneralHashingSource internal constructor(val delegateHashing: HashingSource) : GeneralHashingSource(delegateHashing) {
+	private inner class HashingSourceGeneralHashingSource(val delegateHashing: HashingSource) : GeneralHashingSource(delegateHashing) {
 		override val hash: Hash by lazy(LazyThreadSafetyMode.NONE) {
 			HashingSourceHash(delegateHashing.hash.hex())
 		}
@@ -35,6 +35,7 @@ class HashingSourceHasher internal constructor(private val type: String) : IHash
 			"md5" -> return HashingSourceGeneralHashingSource(HashingSource.md5(delegate))
 			"sha256" -> return HashingSourceGeneralHashingSource(HashingSource.sha256(delegate))
 			"sha512" -> return HashingSourceGeneralHashingSource(HashingSource.sha512(delegate))
+			"sha1" -> return HashingSourceGeneralHashingSource(HashingSource.sha1(delegate))
 		}
 		throw RuntimeException("Invalid hash type provided")
 	}

src/main/kotlin/link/infra/packwiz/installer/request/HandlerManager.kt

@@ -1,6 +1,7 @@
 package link.infra.packwiz.installer.request
 
 import link.infra.packwiz.installer.metadata.SpaceSafeURI
+import link.infra.packwiz.installer.request.handlers.RequestHandlerFile
 import link.infra.packwiz.installer.request.handlers.RequestHandlerGithub
 import link.infra.packwiz.installer.request.handlers.RequestHandlerHTTP
 import okio.Source
@@ -9,9 +10,11 @@ object HandlerManager {
 
 	private val handlers: List<IRequestHandler> = listOf(
 			RequestHandlerGithub(),
-			RequestHandlerHTTP()
+			RequestHandlerHTTP(),
+			RequestHandlerFile()
 	)
 
+	 // TODO: get rid of nullable stuff here
 	@JvmStatic
 	fun getNewLoc(base: SpaceSafeURI?, loc: SpaceSafeURI?): SpaceSafeURI? {
 		if (loc == null) {
@@ -30,6 +33,8 @@ object HandlerManager {
 	// Zip handler discards once read, requesting multiple times on other handlers would cause multiple downloads
 	// Caching system? Copy from already downloaded files?
 
+	// TODO: change to use something more idiomatic than exceptions?
+
 	@JvmStatic
 	@Throws(Exception::class)
 	fun getFileSource(loc: SpaceSafeURI): Source {

src/main/kotlin/link/infra/packwiz/installer/request/RequestExceptions.kt

@@ -0,0 +1,70 @@
+package link.infra.packwiz.installer.request
+
+import okhttp3.Response
+import okio.IOException
+
+sealed class RequestException: Exception {
+	constructor(message: String, cause: Throwable) : super(message, cause)
+	constructor(message: String) : super(message)
+
+	/**
+	 * Internal errors that should not be shown to the user when the code is correct
+	 */
+	sealed class Internal: RequestException {
+		constructor(message: String, cause: Throwable) : super(message, cause)
+		constructor(message: String) : super(message)
+
+		class UnsinkableBase: Internal("Base associated with this path is not a SinkableBase")
+
+		sealed class HTTP: Internal {
+			constructor(message: String, cause: Throwable) : super(message, cause)
+			constructor(message: String) : super(message)
+
+			class NoResponseBody: HTTP("HTTP response in onResponse must have a response body")
+			class RequestFailed(cause: IOException): HTTP("HTTP request failed; may have been cancelled", cause)
+			class IllegalState(cause: IllegalStateException): HTTP("Internal fatal HTTP request error", cause)
+		}
+	}
+
+	/**
+	 * Errors indicating that the request is malformed
+	 */
+	sealed class Validation: RequestException {
+		constructor(message: String, cause: Throwable) : super(message, cause)
+		constructor(message: String) : super(message)
+
+		// TODO: move out of RequestException?
+		class PathContainsNUL(path: String): Validation("Invalid path; contains NUL bytes: ${path.replace("\u0000", "")}")
+		class PathContainsVolumeLetter(path: String): Validation("Invalid path; contains volume letter: $path")
+	}
+
+	/**
+	 * Errors relating to the response from the server
+	 */
+	sealed class Response: RequestException {
+		constructor(message: String, cause: Throwable) : super(message, cause)
+		constructor(message: String) : super(message)
+
+		// TODO: fancier way of displaying this?
+		sealed class HTTP: Response {
+			val response: okhttp3.Response
+
+			constructor(response: okhttp3.Response, message: String, cause: Throwable) : super(message, cause) {
+				this.response = response
+			}
+			constructor(response: okhttp3.Response, message: String) : super(message) {
+				this.response = response
+			}
+
+			class ErrorCode(res: okhttp3.Response): HTTP(res, "Non-successful error code from HTTP request: ${res.code}")
+		}
+
+		sealed class File: RequestException {
+			constructor(message: String, cause: Throwable) : super(message, cause)
+			constructor(message: String) : super(message)
+
+			class FileNotFound(file: String): File("File path not found: $file")
+			class Other(cause: Throwable): File("Failed to read file", cause)
+		}
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/request/handlers/RequestHandlerFile.kt

@@ -0,0 +1,18 @@
+package link.infra.packwiz.installer.request.handlers
+
+import link.infra.packwiz.installer.metadata.SpaceSafeURI
+import link.infra.packwiz.installer.request.IRequestHandler
+import okio.Source
+import okio.source
+import java.nio.file.Paths
+
+open class RequestHandlerFile : IRequestHandler {
+	override fun matchesHandler(loc: SpaceSafeURI): Boolean {
+		return "file" == loc.scheme
+	}
+
+	override fun getFileSource(loc: SpaceSafeURI): Source? {
+		val path = Paths.get(loc.toURL().toURI())
+		return path.source()
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/request/handlers/RequestHandlerGithub.kt

@@ -1,7 +1,6 @@
 package link.infra.packwiz.installer.request.handlers
 
 import link.infra.packwiz.installer.metadata.SpaceSafeURI
-import java.util.*
 import java.util.concurrent.locks.ReentrantReadWriteLock
 import java.util.regex.Pattern
 import kotlin.concurrent.read
@@ -21,7 +20,7 @@ class RequestHandlerGithub : RequestHandlerZip(true) {
 	private val zipUriMap: MutableMap<String, SpaceSafeURI> = HashMap()
 	private val zipUriLock = ReentrantReadWriteLock()
 	private fun getRepoName(loc: SpaceSafeURI): String? {
-		val matcher = repoMatcherPattern.matcher(loc.path)
+		val matcher = repoMatcherPattern.matcher(loc.path ?: return null)
 		return if (matcher.matches()) {
 			matcher.group(1)
 		} else {
@@ -47,7 +46,7 @@ class RequestHandlerGithub : RequestHandlerZip(true) {
 	}
 
 	private fun getBranch(loc: SpaceSafeURI): String? {
-		val matcher = branchMatcherPattern.matcher(loc.path)
+		val matcher = branchMatcherPattern.matcher(loc.path ?: return null)
 		return if (matcher.matches()) {
 			matcher.group(1)
 		} else {
@@ -65,7 +64,7 @@ class RequestHandlerGithub : RequestHandlerZip(true) {
 		if (!("http" == scheme || "https" == scheme)) {
 			return false
 		}
-		return "github.com" == loc.host
-		// TODO: sanity checks, support for more github urls
+		// TODO: more match testing?
+		return "github.com" == loc.host && branchMatcherPattern.matcher(loc.path ?: return false).matches()
 	}
 }

src/main/kotlin/link/infra/packwiz/installer/request/handlers/RequestHandlerHTTP.kt

@@ -4,6 +4,7 @@ import link.infra.packwiz.installer.metadata.SpaceSafeURI
 import link.infra.packwiz.installer.request.IRequestHandler
 import okio.Source
 import okio.source
+import java.net.HttpURLConnection
 
 open class RequestHandlerHTTP : IRequestHandler {
 	override fun matchesHandler(loc: SpaceSafeURI): Boolean {
@@ -12,14 +13,17 @@ open class RequestHandlerHTTP : IRequestHandler {
 	}
 
 	override fun getFileSource(loc: SpaceSafeURI): Source? {
-		val conn = loc.toURL().openConnection()
+		val conn = loc.toURL().openConnection() as HttpURLConnection
 		// TODO: when do we send specific headers??? should there be a way to signal this?
-		// github *sometimes* requires it, sometimes not!
-		//conn.addRequestProperty("Accept", "application/octet-stream");
+		conn.addRequestProperty("Accept", "application/octet-stream")
+		// TODO: include version?
+		conn.addRequestProperty("User-Agent", "packwiz-installer")
+
 		conn.apply {
 			// 30 second read timeout
 			readTimeout = 30 * 1000
+			requestMethod = "GET"
 		}
-		return conn.getInputStream().source()
+		return conn.inputStream.source()
 	}
 }

src/main/kotlin/link/infra/packwiz/installer/request/handlers/RequestHandlerZip.kt

@@ -25,7 +25,7 @@ abstract class RequestHandlerZip(private val modeHasFolder: Boolean) : RequestHa
 		}
 	}
 
-	private inner class ZipReader internal constructor(zip: Source) {
+	private inner class ZipReader(zip: Source) {
 		private val zis = ZipInputStream(zip.buffer().inputStream())
 		private val readFiles: MutableMap<SpaceSafeURI, Buffer> = HashMap()
 		// Write lock implies access to ZipInputStream - only 1 thread must read at a time!

src/main/kotlin/link/infra/packwiz/installer/target/CachedTarget.kt

@@ -0,0 +1,23 @@
+package link.infra.packwiz.installer.target
+
+import link.infra.packwiz.installer.metadata.hash.Hash
+import java.nio.file.Path
+
+data class CachedTarget(
+	/**
+	 * @see Target.name
+	 */
+	val name: String,
+	/**
+	 * The location where the target was last downloaded to.
+	 * This is used for removing old files when the destination path changes.
+	 * This shouldn't be set to the .disabled path (that is manually appended and checked)
+	 */
+	val cachedLocation: Path,
+	val enabled: Boolean,
+	val hash: Hash,
+	/**
+	 * For detecting when a target transitions non-optional -> optional and showing the option selection screen
+	 */
+	val isOptional: Boolean
+)

src/main/kotlin/link/infra/packwiz/installer/target/CachedTargetValidation.kt

@@ -0,0 +1,95 @@
+package link.infra.packwiz.installer.target
+
+import java.io.IOException
+import java.nio.file.*
+import java.nio.file.attribute.BasicFileAttributes
+import kotlin.io.path.relativeTo
+
+data class CachedTargetStatus(val target: CachedTarget, var isValid: Boolean, var markDisabled: Boolean)
+
+fun validate(targets: List<CachedTarget>, baseDir: Path) = runCatching {
+	val results = targets.map {
+		CachedTargetStatus(it, isValid = false, markDisabled = false)
+	}
+	val tree = buildTree(results, baseDir)
+
+	// Efficient file exists checking using directory listing, several orders of magnitude faster than Files.exists calls
+	Files.walkFileTree(baseDir, setOf(FileVisitOption.FOLLOW_LINKS), Int.MAX_VALUE, object : FileVisitor<Path> {
+		var currentNode: PathNode<CachedTargetStatus> = tree
+
+		override fun preVisitDirectory(dir: Path?, attrs: BasicFileAttributes?): FileVisitResult {
+			if (dir == null) {
+				return FileVisitResult.SKIP_SUBTREE
+			}
+			val subdirNode = currentNode.subdirs[dir.getName(dir.nameCount - 1)]
+			return if (subdirNode != null) {
+				currentNode = subdirNode
+				FileVisitResult.CONTINUE
+			} else {
+				FileVisitResult.SKIP_SUBTREE
+			}
+		}
+
+		override fun visitFile(file: Path?, attrs: BasicFileAttributes?): FileVisitResult {
+			if (file == null) {
+				return FileVisitResult.CONTINUE
+			}
+			// TODO: these are relative paths to baseDir
+			// TODO: strip the .disabled for lookup
+			val target = currentNode.files[file.getName(file.nameCount - 1)]
+			if (target != null) {
+				val disabledFile = file.endsWith(".disabled")
+				// If a .disabled file and the actual file both exist, mark as invalid if the target is disabled
+				if ((disabledFile )) {
+
+				}
+			}
+			return FileVisitResult.CONTINUE
+		}
+
+		@Throws(IOException::class)
+		override fun visitFileFailed(file: Path?, exc: IOException?): FileVisitResult {
+			if (exc != null) {
+				throw exc
+			}
+			throw IOException("visitFileFailed called with no exception")
+		}
+
+		@Throws(IOException::class)
+		override fun postVisitDirectory(dir: Path?, exc: IOException?): FileVisitResult {
+			if (exc != null) {
+				throw exc
+			} else {
+				val parent = currentNode.parent
+				if (parent != null) {
+					currentNode = parent
+				} else {
+					throw IOException("Invalid visitor tree structure")
+				}
+				return FileVisitResult.CONTINUE
+			}
+		}
+	})
+
+	results
+}
+
+fun buildTree(targets: List<CachedTargetStatus>, baseDir: Path): PathNode<CachedTargetStatus> {
+	val root = PathNode<CachedTargetStatus>()
+	for (target in targets) {
+		val relPath = target.target.cachedLocation.relativeTo(baseDir)
+		var node = root
+		// Traverse all the directory components, except for the last one
+		for (i in 0 until (relPath.nameCount - 1)) {
+			node = node.createSubdir(relPath.getName(i))
+		}
+		node.files[relPath.getName(relPath.nameCount - 1)] = target
+	}
+	return root
+}
+
+data class PathNode<T>(val subdirs: MutableMap<Path, PathNode<T>>, val files: MutableMap<Path, T>, val parent: PathNode<T>?) {
+	constructor() : this(mutableMapOf(), mutableMapOf(), null)
+
+	fun createSubdir(nextComponent: Path) = subdirs.getOrPut(nextComponent, { PathNode(mutableMapOf(), mutableMapOf(), this) })
+}

src/main/kotlin/link/infra/packwiz/installer/target/ClientHolder.kt

@@ -0,0 +1,12 @@
+package link.infra.packwiz.installer.target
+
+import okhttp3.OkHttpClient
+import okio.FileSystem
+
+class ClientHolder {
+	// TODO: timeouts?
+	// TODO: a button to increase timeouts temporarily when retrying?
+	val okHttpClient by lazy { OkHttpClient.Builder().build() }
+
+	val fileSystem = FileSystem.SYSTEM
+}

src/main/kotlin/link/infra/packwiz/installer/target/OverwriteMode.kt

@@ -0,0 +1,13 @@
+package link.infra.packwiz.installer.target
+
+enum class OverwriteMode {
+	/**
+	 * Overwrite the destination with the source file, if the source file has changed.
+	 */
+	IF_SRC_CHANGED,
+
+	/**
+	 * Never overwrite the destination; if it exists, it should not be written to.
+	 */
+	NEVER
+}

src/main/kotlin/link/infra/packwiz/installer/target/Side.kt

@@ -0,0 +1,54 @@
+package link.infra.packwiz.installer.target
+
+import com.google.gson.annotations.SerializedName
+
+enum class Side {
+	@SerializedName("client")
+	CLIENT("client"),
+	@SerializedName("server")
+	SERVER("server"),
+	@SerializedName("both")
+	@Suppress("unused")
+	BOTH("both", arrayOf(CLIENT, SERVER));
+
+	private val sideName: String
+	private val depSides: Array<Side>?
+
+	constructor(sideName: String) {
+		this.sideName = sideName.toLowerCase()
+		depSides = null
+	}
+
+	constructor(sideName: String, depSides: Array<Side>) {
+		this.sideName = sideName.toLowerCase()
+		this.depSides = depSides
+	}
+
+	override fun toString() = sideName
+
+	fun hasSide(tSide: Side): Boolean {
+		if (this == tSide) {
+			return true
+		}
+		if (depSides != null) {
+			for (depSide in depSides) {
+				if (depSide == tSide) {
+					return true
+				}
+			}
+		}
+		return false
+	}
+
+	companion object {
+		fun from(name: String): Side? {
+			val lowerName = name.toLowerCase()
+			for (side in values()) {
+				if (side.sideName == lowerName) {
+					return side
+				}
+			}
+			return null
+		}
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/target/Target.kt

@@ -0,0 +1,45 @@
+package link.infra.packwiz.installer.target
+
+import link.infra.packwiz.installer.target.path.PackwizPath
+
+// TODO: rename to avoid conflicting with @Target
+interface Target {
+	val src: PackwizPath
+	val dest: PackwizPath
+	val validityToken: ValidityToken
+
+	/**
+	 * Token interface for types used to compare Target identity. Implementations should use equals to indicate that
+	 * these tokens represent the same file; used to preserve optional target choices between file renames.
+	 */
+	interface IdentityToken
+
+	/**
+	 * Default implementation of IdentityToken that assumes files are not renamed; so optional choices do not need to
+	 * be preserved across renames.
+	 */
+	@JvmInline
+	value class PathIdentityToken(val path: String): IdentityToken
+
+	val ident: IdentityToken
+		get() = PathIdentityToken(dest.path)
+
+	/**
+	 * A user-friendly name; defaults to the destination path of the file.
+	 */
+	val name: String
+		get() = dest.path
+	val side: Side
+		get() = Side.BOTH
+	val overwriteMode: OverwriteMode
+		get() = OverwriteMode.IF_SRC_CHANGED
+
+	interface Optional: Target {
+		val optional: Boolean
+		val optionalDefaultValue: Boolean
+	}
+
+	interface OptionalDescribed: Optional {
+		val optionalDescription: String
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/target/ValidityToken.kt

@@ -0,0 +1,16 @@
+package link.infra.packwiz.installer.target
+
+import link.infra.packwiz.installer.metadata.hash.Hash
+
+/**
+ * A token used to determine if the source or destination file is changed, and ensure that the destination file is valid.
+ */
+interface ValidityToken {
+	// TODO: functions to allow validating this from file metadata, from file, or during the download process
+
+	/**
+	 * Default implementation of ValidityToken based on a single hash.
+	 */
+	@JvmInline
+	value class HashValidityToken(val hash: Hash): ValidityToken
+}

src/main/kotlin/link/infra/packwiz/installer/target/path/FilePathBase.kt

@@ -0,0 +1,29 @@
+package link.infra.packwiz.installer.target.path
+
+import link.infra.packwiz.installer.request.RequestException
+import link.infra.packwiz.installer.target.ClientHolder
+import okio.*
+
+data class FilePathBase(private val path: Path): PackwizPath.Base, PackwizPath.SinkableBase {
+	override fun source(path: String, clientHolder: ClientHolder): BufferedSource {
+		val resolved = this.path.resolve(path, true)
+		try {
+			return clientHolder.fileSystem.source(resolved).buffer()
+		} catch (e: FileNotFoundException) {
+			throw RequestException.Response.File.FileNotFound(resolved.toString())
+		} catch (e: IOException) {
+			throw RequestException.Response.File.Other(e)
+		}
+	}
+
+	override fun sink(path: String, clientHolder: ClientHolder): BufferedSink {
+		val resolved = this.path.resolve(path, true)
+		try {
+			return clientHolder.fileSystem.sink(resolved).buffer()
+		} catch (e: FileNotFoundException) {
+			throw RequestException.Response.File.FileNotFound(resolved.toString())
+		} catch (e: IOException) {
+			throw RequestException.Response.File.Other(e)
+		}
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/target/path/HttpUrlBase.kt

@@ -0,0 +1,41 @@
+package link.infra.packwiz.installer.target.path
+
+import link.infra.packwiz.installer.request.RequestException
+import link.infra.packwiz.installer.target.ClientHolder
+import okhttp3.HttpUrl
+import okhttp3.Request
+import okio.BufferedSource
+import okio.IOException
+
+data class HttpUrlBase(private val url: HttpUrl): PackwizPath.Base {
+	private fun resolve(path: String) = url.newBuilder().addPathSegments(path).build()
+
+	override fun source(path: String, clientHolder: ClientHolder): BufferedSource {
+		val req = Request.Builder()
+			.url(resolve(path))
+			.header("Accept", "application/octet-stream")
+			.header("User-Agent", "packwiz-installer")
+			.get()
+			.build()
+		try {
+			val res = clientHolder.okHttpClient.newCall(req).execute()
+			// Can't use .use since it would close the response body before returning it to the caller
+			try {
+				if (!res.isSuccessful) {
+					throw RequestException.Response.HTTP.ErrorCode(res)
+				}
+
+				val body = res.body ?: throw RequestException.Internal.HTTP.NoResponseBody()
+				return body.source()
+			} catch (e: Exception) {
+				// If an exception is thrown, close the response and rethrow
+				res.close()
+				throw e
+			}
+		} catch (e: IOException) {
+			throw RequestException.Internal.HTTP.RequestFailed(e)
+		} catch (e: IllegalStateException) {
+			throw RequestException.Internal.HTTP.IllegalState(e)
+		}
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/target/path/PackwizPath.kt

@@ -0,0 +1,124 @@
+package link.infra.packwiz.installer.target.path
+
+import link.infra.packwiz.installer.request.RequestException
+import link.infra.packwiz.installer.target.ClientHolder
+import okio.BufferedSink
+import okio.BufferedSource
+
+class PackwizPath(path: String, base: Base) {
+	val path: String
+	val base: Base
+
+	init {
+		this.base = base
+
+		// Check for NUL bytes
+		if (path.contains('\u0000')) { throw RequestException.Validation.PathContainsNUL(path) }
+		// Normalise separator, to prevent differences between Unix/Windows
+		val pathNorm = path.replace('\\', '/')
+		// Split, create new lists for output
+		val split = pathNorm.split('/')
+		val canonicalised = mutableListOf<String>()
+
+		// Backward pass: collapse ".." components, remove "." components and empty components (except an empty component at the end; indicating a folder)
+		var parentComponentCount = 0
+		var first = true
+		for (component in split.asReversed()) {
+			if (first) {
+				first = false
+				if (component == "") {
+					canonicalised += component
+				}
+			}
+			// URL-encoded . is normalised
+			val componentNorm = component.replace("%2e", ".")
+			if (componentNorm == "." || componentNorm == "") {
+				// Do nothing
+			} else if (componentNorm == "..") {
+				parentComponentCount++
+			} else if (parentComponentCount > 0) {
+				parentComponentCount--
+			} else {
+				canonicalised += componentNorm
+				// Don't allow volume letters (allows traversal to the root on Windows)
+				if (componentNorm[0] in 'a'..'z' || componentNorm[0] in 'A'..'Z') {
+					if (componentNorm[1] == ':') {
+						throw RequestException.Validation.PathContainsVolumeLetter(path)
+					}
+				}
+			}
+		}
+
+		// Join path
+		this.path = canonicalised.asReversed().joinToString("/")
+	}
+
+	val folder: Boolean get() = path.endsWith("/")
+
+	fun resolve(path: String): PackwizPath {
+		return if (path.startsWith('/') || path.startsWith('\\')) {
+			// Absolute (but still relative to base of pack)
+			PackwizPath(path, base)
+		} else if (folder) {
+			// File in folder; append
+			PackwizPath(this.path + path, base)
+		} else {
+			// File in parent folder; append with parent component
+			PackwizPath(this.path + "/../" + path, base)
+		}
+	}
+
+	/**
+	 * Obtain a BufferedSource for this path
+	 * @throws RequestException When resolving the file failed
+	 */
+	fun source(clientHolder: ClientHolder): BufferedSource = base.source(path, clientHolder)
+
+	/**
+	 * Obtain a BufferedSink for this path
+	 * @throws RequestException.Internal.UnsinkableBase When the base of this path does not have a sink
+	 * @throws RequestException When resolving the file failed
+	 */
+	fun sink(clientHolder: ClientHolder): BufferedSink =
+		if (base is SinkableBase) { base.sink(path, clientHolder) } else { throw RequestException.Internal.UnsinkableBase() }
+
+	interface Base {
+		/**
+		 * Resolve the given (canonical) path against the base, and get a BufferedSource for this file.
+		 * @throws RequestException
+		 */
+		fun source(path: String, clientHolder: ClientHolder): BufferedSource
+
+		operator fun div(path: String) = PackwizPath(path, this)
+	}
+
+	interface SinkableBase: Base {
+		/**
+		 * Resolve the given (canonical) path against the base, and get a BufferedSink for this file.
+		 * @throws RequestException
+		 */
+		fun sink(path: String, clientHolder: ClientHolder): BufferedSink
+	}
+
+	override fun equals(other: Any?): Boolean {
+		if (this === other) return true
+		if (javaClass != other?.javaClass) return false
+
+		other as PackwizPath
+
+		if (path != other.path) return false
+		if (base != other.base) return false
+
+		return true
+	}
+
+	override fun hashCode(): Int {
+		var result = path.hashCode()
+		result = 31 * result + base.hashCode()
+		return result
+	}
+
+	override fun toString(): String {
+		return "base=$base; $path"
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/task/CacheKey.kt

@@ -0,0 +1,3 @@
+package link.infra.packwiz.installer.task
+
+data class CacheKey<T>(val key: String, val version: Int)

src/main/kotlin/link/infra/packwiz/installer/task/CacheManager.kt

@@ -0,0 +1,22 @@
+package link.infra.packwiz.installer.task
+
+import kotlin.reflect.KProperty
+
+class CacheManager {
+	class CacheValue<T> {
+		operator fun getValue(thisVal: Any?, property: KProperty<*>): T {
+			TODO("Not yet implemented")
+		}
+
+		operator fun setValue(thisVal: Any?, property: KProperty<*>, value: T) {
+			TODO("Not yet implemented")
+		}
+
+	}
+
+	operator fun <T> get(cacheKey: CacheKey<T>): CacheValue<T> {
+		return CacheValue()
+	}
+
+
+}

src/main/kotlin/link/infra/packwiz/installer/task/Task.kt

@@ -0,0 +1,20 @@
+package link.infra.packwiz.installer.task
+
+import kotlin.reflect.KMutableProperty0
+
+// TODO: task processing on 1 background thread; actual resolving of values calls out to a thread group
+// TODO: progress bar is updated from each of these tasks
+// TODO: have everything be lazy so there's no need to determine task ordering upfront? a bit like rust async - task results must be queried to occur
+
+abstract class Task<T>(protected val ctx: TaskContext): TaskInput<T> {
+	// TODO: lazy wrapper for fallible results
+	// TODO: multithreaded fanout subclass/helper
+
+	protected fun <T> wasUpdated(value: KMutableProperty0<T>, newValue: T): Boolean {
+		if (value.get() == newValue) {
+			return false
+		}
+		value.set(newValue)
+		return true
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/task/TaskCombinedResult.kt

@@ -0,0 +1,6 @@
+package link.infra.packwiz.installer.task
+
+/**
+ * An object for storing results where result and upToDate are calculated simultaneously
+ */
+data class TaskCombinedResult<T>(val result: T, val upToDate: Boolean)

src/main/kotlin/link/infra/packwiz/installer/task/TaskContext.kt

@@ -0,0 +1,12 @@
+package link.infra.packwiz.installer.task
+
+import link.infra.packwiz.installer.target.ClientHolder
+
+class TaskContext {
+	// TODO: thread pools, protocol roots
+	// TODO: cache management
+
+	val cache = CacheManager()
+
+	val clients = ClientHolder()
+}

src/main/kotlin/link/infra/packwiz/installer/task/TaskInput.kt

@@ -0,0 +1,29 @@
+package link.infra.packwiz.installer.task
+
+import kotlin.reflect.KProperty
+
+interface TaskInput<T> {
+	/**
+	 * The value of this task input. May be lazily evaluated; must be threadsafe.
+	 */
+	val value: T
+
+	/**
+	 * True if the effective value of this input has changed since the task was last run.
+	 * Doesn't require evaluation of the input value; should use cached data if possible.
+	 * May be lazily evaluated; must be threadsafe.
+	 */
+	val upToDate: Boolean
+
+	operator fun getValue(thisVal: Any?, property: KProperty<*>): T = value
+
+	companion object {
+		fun <T> raw(value: T): TaskInput<T> {
+			return object: TaskInput<T> {
+				override val value = value
+				override val upToDate: Boolean
+					get() = false
+			}
+		}
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/task/formats/packwizv1/PackwizV1PackFile.kt

@@ -0,0 +1,6 @@
+package link.infra.packwiz.installer.task.formats.packwizv1
+
+import link.infra.packwiz.installer.metadata.hash.Hash
+import link.infra.packwiz.installer.target.path.PackwizPath
+
+data class PackwizV1PackFile(val name: String, val indexPath: PackwizPath, val indexHash: Hash)

src/main/kotlin/link/infra/packwiz/installer/task/formats/packwizv1/PackwizV1PackTomlTask.kt

@@ -0,0 +1,48 @@
+package link.infra.packwiz.installer.task.formats.packwizv1
+
+import com.google.gson.annotations.SerializedName
+import com.moandjiezana.toml.Toml
+import link.infra.packwiz.installer.metadata.hash.Hash
+import link.infra.packwiz.installer.metadata.hash.HashUtils
+import link.infra.packwiz.installer.target.path.PackwizPath
+import link.infra.packwiz.installer.task.CacheKey
+import link.infra.packwiz.installer.task.Task
+import link.infra.packwiz.installer.task.TaskCombinedResult
+import link.infra.packwiz.installer.task.TaskContext
+import java.io.InputStreamReader
+
+class PackwizV1PackTomlTask(ctx: TaskContext, val path: PackwizPath): Task<PackwizV1PackFile>(ctx) {
+	// TODO: make hierarchically defined by caller? - then changing the pack format type doesn't leave junk in the cache
+	private var cache by ctx.cache[CacheKey<Hash>("packwiz.v1.packtoml.hash", 1)]
+
+	private class PackFile {
+		var name: String? = null
+		var index: IndexFileLoc? = null
+
+		class IndexFileLoc {
+			var file: String? = null
+			@SerializedName("hash-format")
+			var hashFormat: String? = null
+			var hash: String? = null
+		}
+
+		var versions: Map<String, String>? = null
+	}
+
+	private val internalResult by lazy {
+		// TODO: query, parse JSON
+		val packFile = Toml().read(InputStreamReader(path.source(ctx.clients).inputStream(), "UTF-8")).to(PackFile::class.java)
+
+		val resolved = PackwizV1PackFile(packFile.name ?: throw RuntimeException("Name required"), // TODO: better exception handling
+			path.resolve(packFile.index?.file ?: throw RuntimeException("File required")),
+			HashUtils.getHash(packFile.index?.hashFormat ?: throw RuntimeException("Hash format required"),
+				packFile.index?.hash ?: throw RuntimeException("Hash required"))
+		)
+		val hash = HashUtils.getHash("sha256", "whatever was just read")
+
+		TaskCombinedResult(resolved, wasUpdated(::cache, hash))
+	}
+
+	override val value by internalResult::result
+	override val upToDate by internalResult::upToDate
+}

src/main/kotlin/link/infra/packwiz/installer/ui/CLIHandler.kt

@@ -1,47 +0,0 @@
-package link.infra.packwiz.installer.ui
-
-import link.infra.packwiz.installer.ui.IUserInterface.ExceptionListResult
-import java.util.concurrent.CompletableFuture
-import java.util.concurrent.Future
-
-class CLIHandler : IUserInterface {
-	override fun handleException(e: Exception) {
-		e.printStackTrace()
-	}
-
-	override fun show(handler: InputStateHandler) {}
-	override fun submitProgress(progress: InstallProgress) {
-		val sb = StringBuilder()
-		if (progress.hasProgress) {
-			sb.append('(')
-			sb.append(progress.progress)
-			sb.append('/')
-			sb.append(progress.progressTotal)
-			sb.append(") ")
-		}
-		sb.append(progress.message)
-		println(sb.toString())
-	}
-
-	override fun executeManager(task: () -> Unit) {
-		task()
-		println("Finished successfully!")
-	}
-
-	override fun showOptions(options: List<IOptionDetails>): Future<Boolean> {
-		for (opt in options) {
-			opt.optionValue = true
-			// TODO: implement option choice in the CLI?
-			println("Warning: accepting option " + opt.name + " as option choosing is not implemented in the CLI")
-		}
-		return CompletableFuture<Boolean>().apply {
-			complete(false) // Can't be cancelled!
-		}
-	}
-
-	override fun showExceptions(exceptions: List<ExceptionDetails>, numTotal: Int, allowsIgnore: Boolean): Future<ExceptionListResult> {
-		val future = CompletableFuture<ExceptionListResult>()
-		future.complete(ExceptionListResult.CANCEL)
-		return future
-	}
-}

src/main/kotlin/link/infra/packwiz/installer/ui/IUserInterface.kt

@@ -1,35 +1,29 @@
 package link.infra.packwiz.installer.ui
 
-import java.util.concurrent.CompletableFuture
-import java.util.concurrent.Future
-import kotlin.system.exitProcess
+import link.infra.packwiz.installer.ui.data.ExceptionDetails
+import link.infra.packwiz.installer.ui.data.IOptionDetails
+import link.infra.packwiz.installer.ui.data.InstallProgress
 
 interface IUserInterface {
-	fun show(handler: InputStateHandler)
-	fun handleException(e: Exception)
-	@JvmDefault
-	fun handleExceptionAndExit(e: Exception) {
-		handleException(e)
-		exitProcess(1)
-	}
+	fun show()
+	fun dispose()
 
-	@JvmDefault
-	fun setTitle(title: String) {}
+	fun showErrorAndExit(message: String): Nothing {
+		showErrorAndExit(message, null)
+	}
+	fun showErrorAndExit(message: String, e: Exception?): Nothing
+
+	var title: String
 	fun submitProgress(progress: InstallProgress)
-	fun executeManager(task: () -> Unit)
 	// Return true if the installation was cancelled!
-	fun showOptions(options: List<IOptionDetails>): Future<Boolean>
+	fun showOptions(options: List<IOptionDetails>): Boolean
 
-	fun showExceptions(exceptions: List<ExceptionDetails>, numTotal: Int, allowsIgnore: Boolean): Future<ExceptionListResult>
-	@JvmDefault
-	fun disableOptionsButton() {}
+	fun showExceptions(exceptions: List<ExceptionDetails>, numTotal: Int, allowsIgnore: Boolean): ExceptionListResult
+	fun disableOptionsButton(hasOptions: Boolean) {}
 
-	@JvmDefault
-	fun showCancellationDialog(): Future<CancellationResult> {
-		return CompletableFuture<CancellationResult>().apply {
-			complete(CancellationResult.QUIT)
-		}
-	}
+	fun showCancellationDialog(): CancellationResult = CancellationResult.QUIT
+
+	fun awaitOptionalButton(showCancel: Boolean)
 
 	enum class ExceptionListResult {
 		CONTINUE, CANCEL, IGNORE
@@ -38,4 +32,9 @@ interface IUserInterface {
 	enum class CancellationResult {
 		QUIT, CONTINUE
 	}
+
+	var optionsButtonPressed: Boolean
+	var cancelButtonPressed: Boolean
+
+	var firstInstall: Boolean
 }

src/main/kotlin/link/infra/packwiz/installer/ui/InputStateHandler.kt

@@ -1,21 +0,0 @@
-package link.infra.packwiz.installer.ui
-
-class InputStateHandler {
-	// TODO: convert to coroutines/locks?
-	@get:Synchronized
-	var optionsButton = false
-		private set
-	@get:Synchronized
-	var cancelButton = false
-		private set
-
-	@Synchronized
-	fun pressCancelButton() {
-		cancelButton = true
-	}
-
-	@Synchronized
-	fun pressOptionsButton() {
-		optionsButton = true
-	}
-}

src/main/kotlin/link/infra/packwiz/installer/ui/InstallWindow.kt

@@ -1,219 +0,0 @@
-package link.infra.packwiz.installer.ui
-
-import link.infra.packwiz.installer.ui.IUserInterface.ExceptionListResult
-import java.awt.*
-import java.util.concurrent.CompletableFuture
-import java.util.concurrent.Future
-import java.util.concurrent.atomic.AtomicBoolean
-import javax.swing.*
-import javax.swing.border.EmptyBorder
-import kotlin.system.exitProcess
-
-class InstallWindow : IUserInterface {
-	private val frmPackwizlauncher: JFrame
-	private val lblProgresslabel: JLabel
-	private val progressBar: JProgressBar
-	private val btnOptions: JButton
-
-	private var inputStateHandler: InputStateHandler? = null
-	private var title = "Updating modpack..."
-	private var worker: SwingWorkerButWithPublicPublish<Unit, InstallProgress>? = null
-	private val aboutToCrash = AtomicBoolean()
-
-	// TODO: separate JFrame junk from IUserInterface junk?
-
-	init {
-		frmPackwizlauncher = JFrame().apply {
-			title = this@InstallWindow.title
-			setBounds(100, 100, 493, 95)
-			defaultCloseOperation = JFrame.EXIT_ON_CLOSE
-			setLocationRelativeTo(null)
-
-			// Progress bar and loading text
-			add(JPanel().apply {
-				border = EmptyBorder(10, 10, 10, 10)
-				layout = BorderLayout(0, 0)
-
-				progressBar = JProgressBar().apply {
-					isIndeterminate = true
-				}
-				add(progressBar, BorderLayout.CENTER)
-
-				lblProgresslabel = JLabel("Loading...")
-				add(lblProgresslabel, BorderLayout.SOUTH)
-			}, BorderLayout.CENTER)
-
-			// Buttons
-			add(JPanel().apply {
-				border = EmptyBorder(0, 5, 0, 5)
-				layout = GridBagLayout()
-
-				btnOptions = JButton("Optional mods...").apply {
-					alignmentX = Component.CENTER_ALIGNMENT
-
-					addActionListener {
-						text = "Loading..."
-						isEnabled = false
-						inputStateHandler?.pressOptionsButton()
-					}
-				}
-				add(btnOptions, GridBagConstraints().apply {
-					gridx = 0
-					gridy = 0
-				})
-
-				add(JButton("Cancel").apply {
-					addActionListener {
-						isEnabled = false
-						inputStateHandler?.pressCancelButton()
-					}
-				}, GridBagConstraints().apply {
-					gridx = 0
-					gridy = 1
-				})
-			}, BorderLayout.EAST)
-		}
-	}
-
-	override fun show(handler: InputStateHandler) {
-		inputStateHandler = handler
-		EventQueue.invokeLater {
-			try {
-				UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName())
-				frmPackwizlauncher.isVisible = true
-			} catch (e: Exception) {
-				e.printStackTrace()
-			}
-		}
-	}
-
-	override fun handleException(e: Exception) {
-		e.printStackTrace()
-		EventQueue.invokeLater {
-			JOptionPane.showMessageDialog(null,
-					"An error occurred: \n" + e.javaClass.canonicalName + ": " + e.message,
-					title, JOptionPane.ERROR_MESSAGE)
-		}
-	}
-
-	override fun handleExceptionAndExit(e: Exception) {
-		e.printStackTrace()
-		// TODO: Fix this mess
-		// Used to prevent the done() handler of SwingWorker executing if the invokeLater hasn't happened yet
-		aboutToCrash.set(true)
-		EventQueue.invokeLater {
-			JOptionPane.showMessageDialog(null,
-					"A fatal error occurred: \n" + e.javaClass.canonicalName + ": " + e.message,
-					title, JOptionPane.ERROR_MESSAGE)
-			exitProcess(1)
-		}
-		// Pause forever, so it blocks while we wait for System.exit to take effect
-		try {
-			Thread.currentThread().join()
-		} catch (ex: InterruptedException) { // no u
-		}
-	}
-
-	override fun setTitle(title: String) {
-		this.title = title
-		frmPackwizlauncher.let { frame ->
-			EventQueue.invokeLater { frame.title = title }
-		}
-	}
-
-	override fun submitProgress(progress: InstallProgress) {
-		val sb = StringBuilder()
-		if (progress.hasProgress) {
-			sb.append('(')
-			sb.append(progress.progress)
-			sb.append('/')
-			sb.append(progress.progressTotal)
-			sb.append(") ")
-		}
-		sb.append(progress.message)
-		// TODO: better logging library?
-		println(sb.toString())
-		worker?.publishPublic(progress)
-	}
-
-	override fun executeManager(task: Function0<Unit>) {
-		EventQueue.invokeLater {
-			// TODO: rewrite this stupidity to use channels??!!!
-			worker = object : SwingWorkerButWithPublicPublish<Unit, InstallProgress>() {
-				override fun doInBackground() {
-					task.invoke()
-				}
-
-				override fun process(chunks: List<InstallProgress>) {
-					// Only process last chunk
-					if (chunks.isNotEmpty()) {
-						val (message, hasProgress, progress, progressTotal) = chunks[chunks.size - 1]
-						if (hasProgress) {
-							progressBar.isIndeterminate = false
-							progressBar.value = progress
-							progressBar.maximum = progressTotal
-						} else {
-							progressBar.isIndeterminate = true
-							progressBar.value = 0
-						}
-						lblProgresslabel.text = message
-					}
-				}
-
-				override fun done() {
-					if (aboutToCrash.get()) {
-						return
-					}
-					// TODO: a better way to do this?
-					frmPackwizlauncher.dispose()
-					println("Finished successfully!")
-					exitProcess(0)
-				}
-			}.also {
-				it.execute()
-			}
-		}
-	}
-
-	override fun showOptions(options: List<IOptionDetails>): Future<Boolean> {
-		val future = CompletableFuture<Boolean>()
-		EventQueue.invokeLater {
-			OptionsSelectWindow(options, future, frmPackwizlauncher).apply {
-				defaultCloseOperation = JDialog.DISPOSE_ON_CLOSE
-				isVisible = true
-			}
-		}
-		return future
-	}
-
-	override fun showExceptions(exceptions: List<ExceptionDetails>, numTotal: Int, allowsIgnore: Boolean): Future<ExceptionListResult> {
-		val future = CompletableFuture<ExceptionListResult>()
-		EventQueue.invokeLater {
-			ExceptionListWindow(exceptions, future, numTotal, allowsIgnore, frmPackwizlauncher).apply {
-				defaultCloseOperation = JDialog.DISPOSE_ON_CLOSE
-				isVisible = true
-			}
-		}
-		return future
-	}
-
-	override fun disableOptionsButton() {
-		btnOptions.apply {
-			text = "Optional mods..."
-			isEnabled = false
-		}
-	}
-
-	override fun showCancellationDialog(): Future<IUserInterface.CancellationResult> {
-		val future = CompletableFuture<IUserInterface.CancellationResult>()
-		EventQueue.invokeLater {
-			val buttons = arrayOf("Quit", "Ignore")
-			val result = JOptionPane.showOptionDialog(frmPackwizlauncher,
-					"The installation was cancelled. Would you like to quit the game, or ignore the update and start the game?",
-					"Cancelled installation",
-					JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE, null, buttons, buttons[0])
-			future.complete(if (result == 0) IUserInterface.CancellationResult.QUIT else IUserInterface.CancellationResult.CONTINUE)
-		}
-		return future
-	}
-}

src/main/kotlin/link/infra/packwiz/installer/ui/SwingWorkerButWithPublicPublish.kt

@@ -1,13 +0,0 @@
-package link.infra.packwiz.installer.ui
-
-import javax.swing.SwingWorker
-
-// Q: AAA WHAT HAVE YOU DONE THIS IS DISGUSTING
-// A: it just makes things easier, so i can easily have one interface for CLI/GUI
-//    if someone has a better way to do this please PR it
-abstract class SwingWorkerButWithPublicPublish<T, V> : SwingWorker<T, V>() {
-	@SafeVarargs
-	fun publishPublic(vararg chunks: V) {
-		publish(*chunks)
-	}
-}

src/main/kotlin/link/infra/packwiz/installer/ui/cli/CLIHandler.kt

@@ -0,0 +1,66 @@
+package link.infra.packwiz.installer.ui.cli
+
+import link.infra.packwiz.installer.ui.IUserInterface
+import link.infra.packwiz.installer.ui.IUserInterface.ExceptionListResult
+import link.infra.packwiz.installer.ui.data.ExceptionDetails
+import link.infra.packwiz.installer.ui.data.IOptionDetails
+import link.infra.packwiz.installer.ui.data.InstallProgress
+import link.infra.packwiz.installer.util.Log
+import kotlin.system.exitProcess
+
+class CLIHandler : IUserInterface {
+	@Volatile
+	override var optionsButtonPressed = false
+	@Volatile
+	override var cancelButtonPressed = false
+	@Volatile
+	override var firstInstall = false
+
+	override var title: String = ""
+
+	override fun showErrorAndExit(message: String, e: Exception?): Nothing {
+		if (e != null) {
+			Log.fatal(message, e)
+		} else {
+			Log.fatal(message)
+		}
+		exitProcess(1)
+	}
+
+	override fun show() {}
+	override fun dispose() {}
+	override fun submitProgress(progress: InstallProgress) {
+		val sb = StringBuilder()
+		if (progress.hasProgress) {
+			sb.append('(')
+			sb.append(progress.progress)
+			sb.append('/')
+			sb.append(progress.progressTotal)
+			sb.append(") ")
+		}
+		sb.append(progress.message)
+		println(sb.toString())
+	}
+
+	override fun showOptions(options: List<IOptionDetails>): Boolean {
+		for (opt in options) {
+			opt.optionValue = true
+			// TODO: implement option choice in the CLI?
+			Log.warn("Accepting option ${opt.name} as option choosing is not implemented in the CLI")
+		}
+		return false // Can't be cancelled!
+	}
+
+	override fun showExceptions(exceptions: List<ExceptionDetails>, numTotal: Int, allowsIgnore: Boolean): ExceptionListResult {
+		println("Failed to download modpack, the following errors were encountered:")
+		for (ex in exceptions) {
+			print(ex.name + ": ")
+			ex.exception.printStackTrace()
+		}
+		return ExceptionListResult.CANCEL
+	}
+
+	override fun awaitOptionalButton(showCancel: Boolean) {
+		// Do nothing
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/ui/data/ExceptionDetails.kt

@@ -1,4 +1,4 @@
-package link.infra.packwiz.installer.ui
+package link.infra.packwiz.installer.ui.data
 
 data class ExceptionDetails(
 		val name: String,

src/main/kotlin/link/infra/packwiz/installer/ui/data/IOptionDetails.kt

@@ -1,4 +1,4 @@
-package link.infra.packwiz.installer.ui
+package link.infra.packwiz.installer.ui.data
 
 interface IOptionDetails {
 	val name: String

src/main/kotlin/link/infra/packwiz/installer/ui/data/InstallProgress.kt

@@ -1,4 +1,4 @@
-package link.infra.packwiz.installer.ui
+package link.infra.packwiz.installer.ui.data
 
 data class InstallProgress(
 		val message: String,

src/main/kotlin/link/infra/packwiz/installer/ui/gui/ExceptionListWindow.kt

@@ -1,5 +1,7 @@
-package link.infra.packwiz.installer.ui
+package link.infra.packwiz.installer.ui.gui
 
+import link.infra.packwiz.installer.ui.IUserInterface
+import link.infra.packwiz.installer.ui.data.ExceptionDetails
 import java.awt.BorderLayout
 import java.awt.Desktop
 import java.awt.event.WindowAdapter
@@ -16,7 +18,7 @@ import javax.swing.border.EmptyBorder
 class ExceptionListWindow(eList: List<ExceptionDetails>, future: CompletableFuture<IUserInterface.ExceptionListResult>, numTotal: Int, allowsIgnore: Boolean, parentWindow: JFrame?) : JDialog(parentWindow, "Failed file downloads", true) {
 	private val lblExceptionStacktrace: JTextArea
 
-	private class ExceptionListModel internal constructor(private val details: List<ExceptionDetails>) : AbstractListModel<String>() {
+	private class ExceptionListModel(private val details: List<ExceptionDetails>) : AbstractListModel<String>() {
 		override fun getSize() = details.size
 		override fun getElementAt(index: Int) = details[index].name
 		fun getExceptionAt(index: Int) = details[index].exception
@@ -123,7 +125,7 @@ class ExceptionListWindow(eList: List<ExceptionDetails>, future: CompletableFutu
 						if (Desktop.isDesktopSupported() && Desktop.getDesktop().isSupported(Desktop.Action.BROWSE)) {
 							addActionListener {
 								try {
-									Desktop.getDesktop().browse(URI("https://github.com/comp500/packwiz-installer/issues/new"))
+									Desktop.getDesktop().browse(URI("https://github.com/packwiz/packwiz-installer/issues/new"))
 								} catch (e: IOException) {
 									// lol the button just won't work i guess
 								} catch (e: URISyntaxException) {}

src/main/kotlin/link/infra/packwiz/installer/ui/gui/GUIHandler.kt

@@ -0,0 +1,179 @@
+package link.infra.packwiz.installer.ui.gui
+
+import link.infra.packwiz.installer.ui.IUserInterface
+import link.infra.packwiz.installer.ui.IUserInterface.ExceptionListResult
+import link.infra.packwiz.installer.ui.data.ExceptionDetails
+import link.infra.packwiz.installer.ui.data.IOptionDetails
+import link.infra.packwiz.installer.ui.data.InstallProgress
+import link.infra.packwiz.installer.util.Log
+import java.awt.EventQueue
+import java.util.concurrent.CompletableFuture
+import java.util.concurrent.CountDownLatch
+import javax.swing.JDialog
+import javax.swing.JOptionPane
+import javax.swing.UIManager
+import kotlin.system.exitProcess
+
+class GUIHandler : IUserInterface {
+	private lateinit var frmPackwizlauncher: InstallWindow
+
+	@Volatile
+	override var optionsButtonPressed = false
+		set(value) {
+			optionalSelectedLatch.countDown()
+			field = value
+		}
+	@Volatile
+	override var cancelButtonPressed = false
+		set(value) {
+			optionalSelectedLatch.countDown()
+			field = value
+		}
+	var okButtonPressed = false
+		set(value) {
+			optionalSelectedLatch.countDown()
+			field = value
+		}
+	@Volatile
+	override var firstInstall = false
+
+	override var title = "packwiz-installer"
+		set(value) {
+			field = value
+			EventQueue.invokeLater { frmPackwizlauncher.title = value }
+		}
+
+	init {
+		EventQueue.invokeAndWait {
+			try {
+				UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName())
+			} catch (e: Exception) {
+				Log.warn("Failed to set look and feel", e)
+			}
+			frmPackwizlauncher = InstallWindow(this).apply {
+				title = this@GUIHandler.title
+			}
+		}
+	}
+
+	private val visibleCountdownLatch = CountDownLatch(1)
+	private val optionalSelectedLatch = CountDownLatch(1)
+
+	override fun show() = EventQueue.invokeLater {
+		frmPackwizlauncher.isVisible = true
+		visibleCountdownLatch.countDown()
+	}
+
+	override fun dispose() = EventQueue.invokeAndWait {
+		frmPackwizlauncher.dispose()
+	}
+
+	override fun showErrorAndExit(message: String, e: Exception?): Nothing {
+		val buttons = arrayOf("Quit", if (firstInstall) "Continue without installing" else "Continue without updating")
+		if (e != null) {
+			Log.fatal(message, e)
+			EventQueue.invokeAndWait {
+				val result = JOptionPane.showOptionDialog(frmPackwizlauncher,
+					"$message: $e",
+					title,
+					JOptionPane.YES_NO_OPTION, JOptionPane.ERROR_MESSAGE, null, buttons, buttons[0])
+				if (result == 1) {
+					Log.info("User selected to continue without installing/updating, exiting with code 0...")
+					exitProcess(0)
+				} else {
+					Log.info("User selected to quit, exiting with code 1...")
+					exitProcess(1)
+				}
+			}
+		} else {
+			Log.fatal(message)
+			EventQueue.invokeAndWait {
+				val result = JOptionPane.showOptionDialog(frmPackwizlauncher,
+					message,
+					title,
+					JOptionPane.YES_NO_OPTION, JOptionPane.ERROR_MESSAGE, null, buttons, buttons[0])
+				if (result == 1) {
+					Log.info("User selected to continue without installing/updating, exiting with code 0...")
+					exitProcess(0)
+				} else {
+					Log.info("User selected to quit, exiting with code 1...")
+					exitProcess(1)
+				}
+			}
+		}
+		exitProcess(1)
+	}
+
+	override fun submitProgress(progress: InstallProgress) {
+		val sb = StringBuilder()
+		if (progress.hasProgress) {
+			sb.append('(')
+			sb.append(progress.progress)
+			sb.append('/')
+			sb.append(progress.progressTotal)
+			sb.append(") ")
+		}
+		sb.append(progress.message)
+		Log.info(sb.toString())
+		EventQueue.invokeLater {
+			frmPackwizlauncher.displayProgress(progress)
+		}
+	}
+
+	override fun showOptions(options: List<IOptionDetails>): Boolean {
+		val future = CompletableFuture<Boolean>()
+		EventQueue.invokeAndWait {
+			if (options.isEmpty()) {
+				JOptionPane.showMessageDialog(null,
+					"This modpack has no optional mods!",
+					"Optional mods", JOptionPane.INFORMATION_MESSAGE)
+				future.complete(false)
+			} else {
+				OptionsSelectWindow(options, future, frmPackwizlauncher).apply {
+					defaultCloseOperation = JDialog.DISPOSE_ON_CLOSE
+					isVisible = true
+				}
+			}
+		}
+		return future.get()
+	}
+
+	override fun showExceptions(exceptions: List<ExceptionDetails>, numTotal: Int, allowsIgnore: Boolean): ExceptionListResult {
+		val future = CompletableFuture<ExceptionListResult>()
+		EventQueue.invokeLater {
+			ExceptionListWindow(exceptions, future, numTotal, allowsIgnore, frmPackwizlauncher).apply {
+				defaultCloseOperation = JDialog.DISPOSE_ON_CLOSE
+				isVisible = true
+			}
+		}
+		return future.get()
+	}
+
+	override fun disableOptionsButton(hasOptions: Boolean) = EventQueue.invokeLater {
+		frmPackwizlauncher.disableOptionsButton(hasOptions)
+	}
+
+	override fun showCancellationDialog(): IUserInterface.CancellationResult {
+		val future = CompletableFuture<IUserInterface.CancellationResult>()
+		EventQueue.invokeLater {
+			val buttons = arrayOf("Quit", "Ignore")
+			val result = JOptionPane.showOptionDialog(frmPackwizlauncher,
+					"The installation was cancelled. Would you like to quit the game, or ignore the update and start the game?",
+					"Cancelled installation",
+					JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE, null, buttons, buttons[0])
+			future.complete(if (result == 0) IUserInterface.CancellationResult.QUIT else IUserInterface.CancellationResult.CONTINUE)
+		}
+		return future.get()
+	}
+
+	override fun awaitOptionalButton(showCancel: Boolean) {
+		EventQueue.invokeAndWait {
+			frmPackwizlauncher.showOk(!showCancel)
+		}
+		visibleCountdownLatch.await()
+		optionalSelectedLatch.await()
+		EventQueue.invokeLater {
+			frmPackwizlauncher.hideOk()
+		}
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/ui/gui/InstallWindow.kt

@@ -0,0 +1,124 @@
+package link.infra.packwiz.installer.ui.gui
+
+import link.infra.packwiz.installer.ui.data.InstallProgress
+import java.awt.BorderLayout
+import java.awt.Component
+import java.awt.GridBagConstraints
+import java.awt.GridBagLayout
+import javax.swing.*
+import javax.swing.border.EmptyBorder
+
+class InstallWindow(private val handler: GUIHandler) : JFrame() {
+	private var lblProgresslabel: JLabel
+	private var progressBar: JProgressBar
+	private var btnOptions: JButton
+	private val btnCancel: JButton
+	private val btnOk: JButton
+	private val buttonsPanel: JPanel
+
+	init {
+		setBounds(100, 100, 493, 95)
+		// Works better with tiling window managers - there isn't any reason to change window size currently anyway
+		isResizable = false
+		defaultCloseOperation = EXIT_ON_CLOSE
+		setLocationRelativeTo(null)
+
+		// Progress bar and loading text
+		add(JPanel().apply {
+			border = EmptyBorder(10, 10, 10, 10)
+			layout = BorderLayout(0, 0)
+
+			progressBar = JProgressBar().apply {
+				isIndeterminate = true
+			}
+			add(progressBar, BorderLayout.CENTER)
+
+			lblProgresslabel = JLabel("Loading...")
+			add(lblProgresslabel, BorderLayout.SOUTH)
+		}, BorderLayout.CENTER)
+
+		// Buttons
+		buttonsPanel = JPanel().apply {
+			border = EmptyBorder(0, 5, 0, 5)
+			layout = GridBagLayout()
+
+			btnOptions = JButton("Optional mods...").apply {
+				alignmentX = Component.CENTER_ALIGNMENT
+
+				addActionListener {
+					text = "Loading..."
+					isEnabled = false
+					handler.optionsButtonPressed = true
+				}
+			}
+			add(btnOptions, GridBagConstraints().apply {
+				gridx = 1
+				gridy = 0
+			})
+
+			btnCancel = JButton("Cancel").apply {
+				addActionListener {
+					isEnabled = false
+					handler.cancelButtonPressed = true
+				}
+			}
+			add(btnCancel, GridBagConstraints().apply {
+				gridx = 1
+				gridy = 1
+			})
+		}
+
+		btnOk = JButton("Continue").apply {
+			addActionListener {
+				handler.okButtonPressed = true
+			}
+		}
+		add(buttonsPanel, BorderLayout.EAST)
+	}
+
+	fun displayProgress(progress: InstallProgress) {
+		if (progress.hasProgress) {
+			progressBar.isIndeterminate = false
+			progressBar.value = progress.progress
+			progressBar.maximum = progress.progressTotal
+		} else {
+			progressBar.isIndeterminate = true
+			progressBar.value = 0
+		}
+		lblProgresslabel.text = progress.message
+	}
+
+	fun disableOptionsButton(hasOptions: Boolean) {
+		btnOptions.apply {
+			text = if (hasOptions) { "Optional mods..." } else { "No optional mods" }
+ 			isEnabled = false
+		}
+	}
+
+	fun showOk(hideCancel: Boolean) {
+		if (hideCancel) {
+			buttonsPanel.add(btnOk, GridBagConstraints().apply {
+				gridx = 1
+				gridy = 1
+			})
+			buttonsPanel.remove(btnCancel)
+		} else {
+			buttonsPanel.add(btnOk, GridBagConstraints().apply {
+				gridx = 0
+				gridy = 1
+			})
+		}
+		buttonsPanel.revalidate()
+	}
+
+	fun hideOk() {
+		buttonsPanel.remove(btnOk)
+		if (!buttonsPanel.components.contains(btnCancel)) {
+			buttonsPanel.add(btnCancel, GridBagConstraints().apply {
+				gridx = 1
+				gridy = 1
+			})
+		}
+		buttonsPanel.revalidate()
+	}
+}

src/main/kotlin/link/infra/packwiz/installer/ui/gui/OptionTempHandler.kt

@@ -1,4 +1,6 @@
-package link.infra.packwiz.installer.ui
+package link.infra.packwiz.installer.ui.gui
+
+import link.infra.packwiz.installer.ui.data.IOptionDetails
 
 // Serves as a proxy for IOptionDetails, so that setOptionValue isn't called until OK is clicked
 internal class OptionTempHandler(private val opt: IOptionDetails) : IOptionDetails {

src/main/kotlin/link/infra/packwiz/installer/ui/gui/OptionsSelectWindow.kt

@@ -1,5 +1,6 @@
-package link.infra.packwiz.installer.ui
+package link.infra.packwiz.installer.ui.gui
 
+import link.infra.packwiz.installer.ui.data.IOptionDetails
 import java.awt.BorderLayout
 import java.awt.FlowLayout
 import java.awt.event.ActionEvent
@@ -18,7 +19,7 @@ class OptionsSelectWindow internal constructor(optList: List<IOptionDetails>, fu
 	private val tableModel: OptionTableModel
 	private val future: CompletableFuture<Boolean>
 
-	private class OptionTableModel internal constructor(givenOpts: List<IOptionDetails>) : TableModel {
+	private class OptionTableModel(givenOpts: List<IOptionDetails>) : TableModel {
 		private val opts: List<OptionTempHandler>
 
 		init {

src/main/kotlin/link/infra/packwiz/installer/util/Exts.kt

@@ -0,0 +1,38 @@
+package link.infra.packwiz.installer.util
+
+import link.infra.packwiz.installer.ui.IUserInterface
+
+inline fun <T> iflet(value: T?, whenNotNull: (T) -> Unit) {
+	if (value != null) {
+		whenNotNull(value)
+	}
+}
+
+inline fun <T, U> IUserInterface.ifletOrErr(value: T?, message: String, whenNotNull: (T) -> U): U =
+	if (value != null) {
+		whenNotNull(value)
+	} else {
+		this.showErrorAndExit(message)
+	}
+
+inline fun <T, U, V> IUserInterface.ifletOrErr(value: T?, value2: U?, message: String, whenNotNull: (T, U) -> V): V =
+	if (value != null && value2 != null) {
+		whenNotNull(value, value2)
+	} else {
+		this.showErrorAndExit(message)
+	}
+
+inline fun <T> ifletOrWarn(value: T?, message: String, whenNotNull: (T) -> Unit) {
+	if (value != null) {
+		whenNotNull(value)
+	} else {
+		Log.warn(message)
+	}
+}
+
+inline fun <T, U> iflet(value: T?, whenNotNull: (T) -> U, whenNull: () -> U): U =
+	if (value != null) {
+		whenNotNull(value)
+	} else {
+		whenNull()
+	}

src/main/kotlin/link/infra/packwiz/installer/util/Log.kt

@@ -0,0 +1,16 @@
+package link.infra.packwiz.installer.util
+
+object Log {
+	fun info(message: String) = println(message)
+
+	fun warn(message: String) = println("[Warning] $message")
+	fun warn(message: String, exception: Exception) = println("[Warning] $message: $exception")
+
+	fun fatal(message: String) {
+		println("[FATAL] $message")
+	}
+	fun fatal(message: String, exception: Exception) {
+		println("[FATAL] $message: ")
+		exception.printStackTrace()
+	}
+}

src/main/resources/META-INF/LICENSES.md

@@ -0,0 +1,266 @@
+# Licenses
+
+packwiz-installer itself is under the MIT license ([Source](https://github.com/packwiz/packwiz-installer)), except for Murmur2Lib and bundled dependencies as follows:
+
+- Murmur2Lib: Apache 2.0 ([Source](https://github.com/prasanthj/hasher/blob/master/src/main/java/hasher/Murmur2.java))
+  - Copyright 2014 Prasanth Jayachandran
+- Google Gson 2.8.9: Apache 2.0 ([Source](https://github.com/google/gson))
+  - Copyright 2008 Google Inc.
+- Okio 3.0.0: Apache 2.0 ([Source](https://github.com/square/okio/))
+  - Copyright 2013 Square, Inc.
+- Commons CLI 1.5: Apache 2.0 ([Source](http://commons.apache.org/proper/commons-cli/))
+- Jetbrains Annotations 13.0: Apache 2.0 ([Source](https://github.com/JetBrains/java-annotations))
+  - Copyright 2000-2016 JetBrains s.r.o.
+- Kotlin Standard Library 1.6.10: Apache 2.0 ([Source](https://github.com/JetBrains/kotlin))
+  - Copyright 2010-2020 JetBrains s.r.o and respective authors and developers
+- toml4j 0.7.2: MIT ([Source](https://github.com/mwanji/toml4j))
+  - Copyright (c) 2013-2015 Moandji Ezana
+- kotlin-result 1.1.14: ISC ([Source](https://github.com/michaelbull/kotlin-result))
+  - Copyright (c) 2017-2022 Michael Bull (https://www.michael-bull.com)
+
+## Associated notices
+
+### Commons CLI
+Apache Commons CLI
+Copyright 2001-2017 The Apache Software Foundation
+
+This product includes software developed at
+The Apache Software Foundation (http://www.apache.org/).
+
+## Full license texts
+
+### MIT
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
+### Apache 2.0
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
+
+   "License" shall mean the terms and conditions for use, reproduction,
+   and distribution as defined by Sections 1 through 9 of this document.
+
+   "Licensor" shall mean the copyright owner or entity authorized by
+   the copyright owner that is granting the License.
+
+   "Legal Entity" shall mean the union of the acting entity and all
+   other entities that control, are controlled by, or are under common
+   control with that entity. For the purposes of this definition,
+   "control" means (i) the power, direct or indirect, to cause the
+   direction or management of such entity, whether by contract or
+   otherwise, or (ii) ownership of fifty percent (50%) or more of the
+   outstanding shares, or (iii) beneficial ownership of such entity.
+
+   "You" (or "Your") shall mean an individual or Legal Entity
+   exercising permissions granted by this License.
+
+   "Source" form shall mean the preferred form for making modifications,
+   including but not limited to software source code, documentation
+   source, and configuration files.
+
+   "Object" form shall mean any form resulting from mechanical
+   transformation or translation of a Source form, including but
+   not limited to compiled object code, generated documentation,
+   and conversions to other media types.
+
+   "Work" shall mean the work of authorship, whether in Source or
+   Object form, made available under the License, as indicated by a
+   copyright notice that is included in or attached to the work
+   (an example is provided in the Appendix below).
+
+   "Derivative Works" shall mean any work, whether in Source or Object
+   form, that is based on (or derived from) the Work and for which the
+   editorial revisions, annotations, elaborations, or other modifications
+   represent, as a whole, an original work of authorship. For the purposes
+   of this License, Derivative Works shall not include works that remain
+   separable from, or merely link (or bind by name) to the interfaces of,
+   the Work and Derivative Works thereof.
+
+   "Contribution" shall mean any work of authorship, including
+   the original version of the Work and any modifications or additions
+   to that Work or Derivative Works thereof, that is intentionally
+   submitted to Licensor for inclusion in the Work by the copyright owner
+   or by an individual or Legal Entity authorized to submit on behalf of
+   the copyright owner. For the purposes of this definition, "submitted"
+   means any form of electronic, verbal, or written communication sent
+   to the Licensor or its representatives, including but not limited to
+   communication on electronic mailing lists, source code control systems,
+   and issue tracking systems that are managed by, or on behalf of, the
+   Licensor for the purpose of discussing and improving the Work, but
+   excluding communication that is conspicuously marked or otherwise
+   designated in writing by the copyright owner as "Not a Contribution."
+
+   "Contributor" shall mean Licensor and any individual or Legal Entity
+   on behalf of whom a Contribution has been received by Licensor and
+   subsequently incorporated within the Work.
+
+2. Grant of Copyright License. Subject to the terms and conditions of
+   this License, each Contributor hereby grants to You a perpetual,
+   worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+   copyright license to reproduce, prepare Derivative Works of,
+   publicly display, publicly perform, sublicense, and distribute the
+   Work and such Derivative Works in Source or Object form.
+
+3. Grant of Patent License. Subject to the terms and conditions of
+   this License, each Contributor hereby grants to You a perpetual,
+   worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+   (except as stated in this section) patent license to make, have made,
+   use, offer to sell, sell, import, and otherwise transfer the Work,
+   where such license applies only to those patent claims licensable
+   by such Contributor that are necessarily infringed by their
+   Contribution(s) alone or by combination of their Contribution(s)
+   with the Work to which such Contribution(s) was submitted. If You
+   institute patent litigation against any entity (including a
+   cross-claim or counterclaim in a lawsuit) alleging that the Work
+   or a Contribution incorporated within the Work constitutes direct
+   or contributory patent infringement, then any patent licenses
+   granted to You under this License for that Work shall terminate
+   as of the date such litigation is filed.
+
+4. Redistribution. You may reproduce and distribute copies of the
+   Work or Derivative Works thereof in any medium, with or without
+   modifications, and in Source or Object form, provided that You
+   meet the following conditions:
+
+   (a) You must give any other recipients of the Work or
+   Derivative Works a copy of this License; and
+
+   (b) You must cause any modified files to carry prominent notices
+   stating that You changed the files; and
+
+   (c) You must retain, in the Source form of any Derivative Works
+   that You distribute, all copyright, patent, trademark, and
+   attribution notices from the Source form of the Work,
+   excluding those notices that do not pertain to any part of
+   the Derivative Works; and
+
+   (d) If the Work includes a "NOTICE" text file as part of its
+   distribution, then any Derivative Works that You distribute must
+   include a readable copy of the attribution notices contained
+   within such NOTICE file, excluding those notices that do not
+   pertain to any part of the Derivative Works, in at least one
+   of the following places: within a NOTICE text file distributed
+   as part of the Derivative Works; within the Source form or
+   documentation, if provided along with the Derivative Works; or,
+   within a display generated by the Derivative Works, if and
+   wherever such third-party notices normally appear. The contents
+   of the NOTICE file are for informational purposes only and
+   do not modify the License. You may add Your own attribution
+   notices within Derivative Works that You distribute, alongside
+   or as an addendum to the NOTICE text from the Work, provided
+   that such additional attribution notices cannot be construed
+   as modifying the License.
+
+   You may add Your own copyright statement to Your modifications and
+   may provide additional or different license terms and conditions
+   for use, reproduction, or distribution of Your modifications, or
+   for any such Derivative Works as a whole, provided Your use,
+   reproduction, and distribution of the Work otherwise complies with
+   the conditions stated in this License.
+
+5. Submission of Contributions. Unless You explicitly state otherwise,
+   any Contribution intentionally submitted for inclusion in the Work
+   by You to the Licensor shall be under the terms and conditions of
+   this License, without any additional terms or conditions.
+   Notwithstanding the above, nothing herein shall supersede or modify
+   the terms of any separate license agreement you may have executed
+   with Licensor regarding such Contributions.
+
+6. Trademarks. This License does not grant permission to use the trade
+   names, trademarks, service marks, or product names of the Licensor,
+   except as required for reasonable and customary use in describing the
+   origin of the Work and reproducing the content of the NOTICE file.
+
+7. Disclaimer of Warranty. Unless required by applicable law or
+   agreed to in writing, Licensor provides the Work (and each
+   Contributor provides its Contributions) on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+   implied, including, without limitation, any warranties or conditions
+   of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+   PARTICULAR PURPOSE. You are solely responsible for determining the
+   appropriateness of using or redistributing the Work and assume any
+   risks associated with Your exercise of permissions under this License.
+
+8. Limitation of Liability. In no event and under no legal theory,
+   whether in tort (including negligence), contract, or otherwise,
+   unless required by applicable law (such as deliberate and grossly
+   negligent acts) or agreed to in writing, shall any Contributor be
+   liable to You for damages, including any direct, indirect, special,
+   incidental, or consequential damages of any character arising as a
+   result of this License or out of the use or inability to use the
+   Work (including but not limited to damages for loss of goodwill,
+   work stoppage, computer failure or malfunction, or any and all
+   other commercial damages or losses), even if such Contributor
+   has been advised of the possibility of such damages.
+
+9. Accepting Warranty or Additional Liability. While redistributing
+   the Work or Derivative Works thereof, You may choose to offer,
+   and charge a fee for, acceptance of support, warranty, indemnity,
+   or other liability obligations and/or rights consistent with this
+   License. However, in accepting such obligations, You may act only
+   on Your own behalf and on Your sole responsibility, not on behalf
+   of any other Contributor, and only if You agree to indemnify,
+   defend, and hold each Contributor harmless for any liability
+   incurred by, or claims asserted against, such Contributor by reason
+   of your accepting any such warranty or additional liability.
+
+END OF TERMS AND CONDITIONS
+
+APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
+      replaced with your own identifying information. (Don't include
+      the brackets!)  The text should be enclosed in the appropriate
+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
+      same "printed page" as the copyright notice for easier
+      identification within third-party archives.
+
+Copyright [yyyy] [name of copyright owner]
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+### ISC
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.