Add JvmStatic to fix --help command (bootstrapper calls these)

.gitignore

@@ -1,74 +1,87 @@
-# Created by https://www.gitignore.io/api/java,gradle,eclipse
-# Edit at https://www.gitignore.io/?templates=java,gradle,eclipse
 
-### Eclipse ###
-.metadata
-bin/
-tmp/
-*.tmp
-*.bak
-*.swp
-*~.nib
-local.properties
-.settings/
-.loadpath
-.recommenders
+# Created by https://www.gitignore.io/api/java,gradle,intellij
+# Edit at https://www.gitignore.io/?templates=java,gradle,intellij
 
-# External tool builders
-.externalToolBuilders/
+### Intellij ###
+# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio and WebStorm
+# Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839
 
-# Locally stored "Eclipse launch configurations"
-*.launch
+# User-specific stuff
+.idea/**/workspace.xml
+.idea/**/tasks.xml
+.idea/**/usage.statistics.xml
+.idea/**/dictionaries
+.idea/**/shelf
 
-# PyDev specific (Python IDE for Eclipse)
-*.pydevproject
+# Generated files
+.idea/**/contentModel.xml
 
-# CDT-specific (C/C++ Development Tooling)
-.cproject
+# Sensitive or high-churn files
+.idea/**/dataSources/
+.idea/**/dataSources.ids
+.idea/**/dataSources.local.xml
+.idea/**/sqlDataSources.xml
+.idea/**/dynamic.xml
+.idea/**/uiDesigner.xml
+.idea/**/dbnavigator.xml
 
-# CDT- autotools
-.autotools
+# Gradle
+.idea/**/gradle.xml
+.idea/**/libraries
 
-# Java annotation processor (APT)
-.factorypath
+# Gradle and Maven with auto-import
+# 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/modules.xml
+# .idea/*.iml
+# .idea/modules
+# *.iml
+# *.ipr
 
-# PDT-specific (PHP Development Tools)
-.buildpath
+# CMake
+cmake-build-*/
 
-# sbteclipse plugin
-.target
+# Mongo Explorer plugin
+.idea/**/mongoSettings.xml
 
-# Tern plugin
-.tern-project
+# File-based project format
+*.iws
 
-# TeXlipse plugin
-.texlipse
+# IntelliJ
+out/
 
-# STS (Spring Tool Suite)
-.springBeans
+# mpeltonen/sbt-idea plugin
+.idea_modules/
 
-# Code Recommenders
-.recommenders/
+# JIRA plugin
+atlassian-ide-plugin.xml
 
-# Annotation Processing
-.apt_generated/
+# Cursive Clojure plugin
+.idea/replstate.xml
 
-# Scala IDE specific (Scala & Java development for Eclipse)
-.cache-main
-.scala_dependencies
-.worksheet
+# Crashlytics plugin (for Android Studio and IntelliJ)
+com_crashlytics_export_strings.xml
+crashlytics.properties
+crashlytics-build.properties
+fabric.properties
 
-### Eclipse Patch ###
-# Eclipse Core
-.project
+# Editor-based Rest Client
+.idea/httpRequests
 
-# JDT-specific (Eclipse Java Development Tools)
-.classpath
+# Android studio 3.1+ serialized cache file
+.idea/caches/build_file_checksums.ser
 
-# Annotation Processing
-.apt_generated
+### Intellij Patch ###
+# Comment Reason: https://github.com/joeblau/gitignore.io/issues/186#issuecomment-215987721
 
-.sts4-cache/
+# *.iml
+# modules.xml
+# .idea/misc.xml
+# *.ipr
+
+# Sonarlint plugin
+.idea/sonarlint
 
 ### Java ###
 # Compiled class file
@@ -114,4 +127,4 @@ gradle-app.setting
 ### Gradle Patch ###
 **/build/
 
-# End of https://www.gitignore.io/api/java,gradle,eclipse
+# End of https://www.gitignore.io/api/java,gradle,intellij

.idea/codeStyles/codeStyleConfig.xml

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

.idea/compiler.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="CompilerConfiguration">
+    <bytecodeTargetLevel target="1.8" />
+  </component>
+</project>

.idea/inspectionProfiles/Project_Default.xml

@@ -0,0 +1,36 @@
+<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

@@ -0,0 +1,20 @@
+<?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

@@ -0,0 +1,10 @@
+<?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/packwiz-installer.iml

@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4" />

.idea/vcs.xml

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

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

@@ -1,34 +0,0 @@
-plugins {
-    id 'java'
-    id 'application'
-    id 'com.github.johnrengelman.shadow' version '5.0.0'
-    id 'com.palantir.git-version' version '0.11.0'
-}
-
-dependencies {
-	implementation 'commons-cli:commons-cli:1.4'
-    //testImplementation 'junit:junit:4.12'
-}
-
-repositories {
-    jcenter()
-}
-
-mainClassName = 'link.infra.packwiz.installer.RequiresBootstrap'
-version gitVersion()
-
-jar {
-    manifest {
-        attributes(
-            'Main-Class': 'link.infra.packwiz.installer.RequiresBootstrap',
-            'Implementation-Version': project.version
-        )
-    }
-}
-
-// Commons CLI is already included in packwiz-installer-bootstrap
-shadowJar {
-   dependencies {
-       exclude(dependency('commons-cli:commons-cli:1.4'))
-   }
-}

build.gradle.kts

@@ -0,0 +1,88 @@
+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"
+}
+
+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 {
+	jcenter()
+}
+
+application {
+	mainClassName = "link.infra.packwiz.installer.RequiresBootstrap"
+}
+
+val gitVersion: groovy.lang.Closure<*> by extra
+version = gitVersion()
+
+tasks.jar {
+	manifest {
+		attributes["Main-Class"] = "link.infra.packwiz.installer.RequiresBootstrap"
+		attributes["Implementation-Version"] = project.version
+	}
+}
+
+// Commons CLI and Minimal JSON are already included in packwiz-installer-bootstrap
+tasks.shadowJar {
+	dependencies {
+		exclude(dependency("commons-cli:commons-cli:1.4"))
+		exclude(dependency("com.eclipsesource.minimal-json:minimal-json:0.9.5"))
+	}
+}
+
+// Used for vscode launch.json
+tasks.register<Copy>("copyJar") {
+	from(tasks.shadowJar)
+	rename("packwiz-installer-(.*)\\.jar", "packwiz-installer.jar")
+	into("build/libs/")
+}
+
+tasks.build {
+	dependsOn("copyJar")
+}
+
+if (project.hasProperty("github.token")) {
+	githubRelease {
+		owner("comp500")
+		repo("packwiz-installer")
+		tagName("${project.version}")
+		releaseName("Release ${project.version}")
+		draft(true)
+		token(findProperty("github.token") as String? ?: "")
+		releaseAssets(tasks.jar.get().destinationDirectory.file("packwiz-installer.jar").get())
+	}
+
+	tasks.githubRelease {
+		dependsOn(tasks.build)
+	}
+}
+
+tasks.compileKotlin {
+	kotlinOptions {
+		jvmTarget = "1.8"
+		freeCompilerArgs = listOf("-Xjvm-default=enable")
+	}
+}
+tasks.compileTestKotlin {
+	kotlinOptions {
+		jvmTarget = "1.8"
+		freeCompilerArgs = listOf("-Xjvm-default=enable")
+	}
+}

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

@@ -1,99 +0,0 @@
-package link.infra.packwiz.installer;
-
-import java.awt.BorderLayout;
-import java.awt.Component;
-import java.awt.EventQueue;
-import java.awt.GridBagConstraints;
-import java.awt.GridBagLayout;
-
-import javax.swing.JButton;
-import javax.swing.JFrame;
-import javax.swing.JLabel;
-import javax.swing.JPanel;
-import javax.swing.JProgressBar;
-import javax.swing.UIManager;
-import javax.swing.border.EmptyBorder;
-import java.awt.event.ActionListener;
-import java.awt.event.ActionEvent;
-
-public class InstallWindow {
-	
-	// TODO: move to seperate file, make usable without GUI
-
-	private JFrame frmPackwizlauncher;
-	private UpdateManager updateManager = new UpdateManager();
-
-	/**
-	 * Launch the application.
-	 */
-	public static void main(String[] args) {
-		EventQueue.invokeLater(new Runnable() {
-			public void run() {
-				try {
-					UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
-					InstallWindow window = new InstallWindow();
-					window.frmPackwizlauncher.setVisible(true);
-				} catch (Exception e) {
-					e.printStackTrace();
-				}
-			}
-		});
-	}
-
-	/**
-	 * Create the application.
-	 */
-	public InstallWindow() {
-		initialize();
-	}
-
-	/**
-	 * Initialize the contents of the frame.
-	 */
-	private void initialize() {
-		frmPackwizlauncher = new JFrame();
-		frmPackwizlauncher.setTitle("Updating modpack...");
-		frmPackwizlauncher.setBounds(100, 100, 493, 95);
-		frmPackwizlauncher.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
-		frmPackwizlauncher.setLocationRelativeTo(null);
-		
-		JPanel panel = new JPanel();
-		panel.setBorder(new EmptyBorder(10, 10, 10, 10));
-		frmPackwizlauncher.getContentPane().add(panel, BorderLayout.CENTER);
-		panel.setLayout(new BorderLayout(0, 0));
-		
-		JProgressBar progressBar = new JProgressBar();
-		progressBar.setValue(50);
-		panel.add(progressBar, BorderLayout.CENTER);
-		
-		JLabel lblProgresslabel = new JLabel("Loading...");
-		panel.add(lblProgresslabel, BorderLayout.SOUTH);
-		
-		JPanel panel_1 = new JPanel();
-		panel_1.setBorder(new EmptyBorder(0, 5, 0, 5));
-		frmPackwizlauncher.getContentPane().add(panel_1, BorderLayout.EAST);
-		GridBagLayout gbl_panel_1 = new GridBagLayout();
-		panel_1.setLayout(gbl_panel_1);
-		
-		JButton btnOptions = new JButton("Options...");
-		btnOptions.setAlignmentX(Component.CENTER_ALIGNMENT);
-		GridBagConstraints gbc_btnOptions = new GridBagConstraints();
-		gbc_btnOptions.gridx = 0;
-		gbc_btnOptions.gridy = 0;
-		panel_1.add(btnOptions, gbc_btnOptions);
-		
-		JButton btnCancel = new JButton("Cancel");
-		btnCancel.addActionListener(new ActionListener() {
-			public void actionPerformed(ActionEvent arg0) {
-				updateManager.cleanup();
-				frmPackwizlauncher.dispose();
-			}
-		});
-		btnCancel.setAlignmentX(Component.CENTER_ALIGNMENT);
-		GridBagConstraints gbc_btnCancel = new GridBagConstraints();
-		gbc_btnCancel.gridx = 0;
-		gbc_btnCancel.gridy = 1;
-		panel_1.add(btnCancel, gbc_btnCancel);
-	}
-
-}

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

@@ -1,53 +0,0 @@
-package link.infra.packwiz.installer;
-
-import javax.swing.JOptionPane;
-import javax.swing.UIManager;
-
-import org.apache.commons.cli.CommandLine;
-import org.apache.commons.cli.CommandLineParser;
-import org.apache.commons.cli.DefaultParser;
-import org.apache.commons.cli.Options;
-import org.apache.commons.cli.ParseException;
-
-public class Main {
-	
-	// Actual main() is in RequiresBootstrap!
-	
-	public Main(String[] args) {
-		Options options = new Options();
-		addNonBootstrapOptions(options);
-		addBootstrapOptions(options);
-		
-		CommandLineParser parser = new DefaultParser();
-		CommandLine cmd = null;
-		try {
-			cmd = parser.parse(options, args);
-		} catch (ParseException e) {
-			e.printStackTrace();
-			try {
-				UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
-			} catch (Exception e1) {
-				// Ignore the exceptions, just continue using the ugly L&F
-			}
-			JOptionPane.showMessageDialog(null, e.getMessage(), "packwiz-installer", JOptionPane.ERROR_MESSAGE);
-			System.exit(1);
-		}
-		
-		System.out.println("Hello World!");
-	}
-
-	// Called by packwiz-installer-bootstrap to set up the help command
-	public static void addNonBootstrapOptions(Options options) {
-		//options.addOption("w", "welp", false, "Testing options");
-	}
-	
-	// TODO: link these somehow so they're only defined once?
-	private static void addBootstrapOptions(Options options) {
-		options.addOption(null, "bootstrap-update-url", true, "Github API URL for checking for updates");
-		options.addOption(null, "bootstrap-no-update", false, "Don't update packwiz-installer");
-		options.addOption(null, "bootstrap-main-jar", true, "Location of the packwiz-installer JAR file");
-		options.addOption("g", "no-gui", false, "Don't display a GUI to show update progress");
-		options.addOption("h", "help", false, "Display this message");
-	}
-	
-}

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

@@ -1,10 +1,8 @@
 package link.infra.packwiz.installer;
 
+import javax.swing.*;
 import java.util.Arrays;
 
-import javax.swing.JOptionPane;
-import javax.swing.UIManager;
-
 public class RequiresBootstrap {
 
 	public static void main(String[] args) {
@@ -15,10 +13,10 @@ public class RequiresBootstrap {
 		if (Arrays.stream(args).map(str -> {
 			if (str == null) return "";
 			if (str.startsWith("--")) {
-				return str.substring(2, str.length());
+				return str.substring(2);
 			}
 			if (str.startsWith("-")) {
-				return str.substring(1, str.length());
+				return str.substring(1);
 			}
 			return "";
 		}).anyMatch(str -> str.equals("g") || str.equals("no-gui"))) {

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

@@ -1,9 +0,0 @@
-package link.infra.packwiz.installer;
-
-public class UpdateManager {
-	Thread updateThread = new Thread(new UpdateThread());
-	
-	public void cleanup() {
-		
-	}
-}

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

@@ -1,10 +0,0 @@
-package link.infra.packwiz.installer;
-
-public class UpdateThread implements Runnable {
-
-	@Override
-	public void run() {
-		
-	}
-
-}

src/main/java/link/infra/packwiz/installer/metadata/hash/Murmur2Lib.java

@@ -0,0 +1,166 @@
+// Obtained from https://github.com/prasanthj/hasher/blob/master/src/main/java/hasher/Murmur2.java
+/**
+ *   Copyright 2014 Prasanth Jayachandran
+ *
+ * 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.
+ */
+package link.infra.packwiz.installer.metadata.hash;
+
+/**
+ * Murmur2 32 and 64 bit variants.
+ * 32-bit Java port of https://code.google.com/p/smhasher/source/browse/trunk/MurmurHash2.cpp#37
+ * 64-bit Java port of https://code.google.com/p/smhasher/source/browse/trunk/MurmurHash2.cpp#96
+ */
+public class Murmur2Lib {
+  // Constants for 32-bit variant
+  private static final int M_32 = 0x5bd1e995;
+  private static final int R_32 = 24;
+
+  // Constants for 64-bit variant
+  private static final long M_64 = 0xc6a4a7935bd1e995L;
+  private static final int R_64 = 47;
+  private static final int DEFAULT_SEED = 0;
+
+  /**
+   * Murmur2 32-bit variant.
+   *
+   * @param data - input byte array
+   * @return - hashcode
+   */
+  public static int hash32(byte[] data) {
+    return hash32(data, data.length, DEFAULT_SEED);
+  }
+
+  /**
+   * Murmur2 32-bit variant.
+   *
+   * @param data   - input byte array
+   * @param length - length of array
+   * @param seed   - seed. (default 0)
+   * @return - hashcode
+   */
+  public static int hash32(byte[] data, int length, int seed) {
+    int h = seed ^ length;
+    int len_4 = length >> 2;
+
+    // body
+    for (int i = 0; i < len_4; i++) {
+      int i_4 = i << 2;
+      int k = (data[i_4] & 0xff)
+          | ((data[i_4 + 1] & 0xff) << 8)
+          | ((data[i_4 + 2] & 0xff) << 16)
+          | ((data[i_4 + 3] & 0xff) << 24);
+
+      // mix functions
+      k *= M_32;
+      k ^= k >>> R_32;
+      k *= M_32;
+      h *= M_32;
+      h ^= k;
+    }
+
+    // tail
+    int len_m = len_4 << 2;
+    int left = length - len_m;
+    if (left != 0) {
+      if (left >= 3) {
+        h ^= (int) data[length - (left - 2)] << 16;
+      }
+      if (left >= 2) {
+        h ^= (int) data[length - (left - 1)] << 8;
+      }
+      if (left >= 1) {
+        h ^= data[length - left];
+      }
+
+      h *= M_32;
+    }
+
+    // finalization
+    h ^= h >>> 13;
+    h *= M_32;
+    h ^= h >>> 15;
+
+    return h;
+  }
+
+  /**
+   * Murmur2 64-bit variant.
+   *
+   * @param data - input byte array
+   * @return - hashcode
+   */
+  public static long hash64(final byte[] data) {
+    return hash64(data, data.length, DEFAULT_SEED);
+  }
+
+  /**
+   * Murmur2 64-bit variant.
+   *
+   * @param data   - input byte array
+   * @param length - length of array
+   * @param seed   - seed. (default 0)
+   * @return - hashcode
+   */
+  public static long hash64(final byte[] data, int length, int seed) {
+    long h = (seed & 0xffffffffl) ^ (length * M_64);
+    int length8 = length >> 3;
+
+    // body
+    for (int i = 0; i < length8; i++) {
+      final int i8 = i << 3;
+      long k = ((long) data[i8] & 0xff)
+          | (((long) data[i8 + 1] & 0xff) << 8)
+          | (((long) data[i8 + 2] & 0xff) << 16)
+          | (((long) data[i8 + 3] & 0xff) << 24)
+          | (((long) data[i8 + 4] & 0xff) << 32)
+          | (((long) data[i8 + 5] & 0xff) << 40)
+          | (((long) data[i8 + 6] & 0xff) << 48)
+          | (((long) data[i8 + 7] & 0xff) << 56);
+
+      // mix functions
+      k *= M_64;
+      k ^= k >>> R_64;
+      k *= M_64;
+      h ^= k;
+      h *= M_64;
+    }
+
+    // tail
+    int tailStart = length8 << 3;
+    switch (length - tailStart) {
+      case 7:
+        h ^= (long) (data[tailStart + 6] & 0xff) << 48;
+      case 6:
+        h ^= (long) (data[tailStart + 5] & 0xff) << 40;
+      case 5:
+        h ^= (long) (data[tailStart + 4] & 0xff) << 32;
+      case 4:
+        h ^= (long) (data[tailStart + 3] & 0xff) << 24;
+      case 3:
+        h ^= (long) (data[tailStart + 2] & 0xff) << 16;
+      case 2:
+        h ^= (long) (data[tailStart + 1] & 0xff) << 8;
+      case 1:
+        h ^= data[tailStart] & 0xff;
+        h *= M_64;
+    }
+
+    // finalization
+    h ^= h >>> R_64;
+    h *= M_64;
+    h ^= h >>> R_64;
+
+    return h;
+  }
+}

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

@@ -0,0 +1,241 @@
+package link.infra.packwiz.installer
+
+import link.infra.packwiz.installer.metadata.IndexFile
+import link.infra.packwiz.installer.metadata.ManifestFile
+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 java.io.IOException
+import java.nio.file.Files
+import java.nio.file.Paths
+import java.nio.file.StandardCopyOption
+import java.util.*
+
+internal class DownloadTask private constructor(val metadata: IndexFile.File, defaultFormat: String, private val downloadSide: UpdateManager.Options.Side) : IOptionDetails {
+	var cachedFile: ManifestFile.File? = null
+
+	private var err: Exception? = null
+	val exceptionDetails get() = err?.let { e -> ExceptionDetails(name, e) }
+
+	fun failed() = err != null
+
+	private 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
+	private var newOptional = true
+
+	val isOptional get() = metadata.linkedFile?.isOptional ?: false
+
+	fun isNewOptional() = isOptional && newOptional
+
+	fun correctSide() = metadata.linkedFile?.side?.hasSide(downloadSide) ?: true
+
+	override val name get() = metadata.name
+
+	// Ensure that an update is done if it changes from false to true, or from true to false
+	override var optionValue: Boolean
+		get() = cachedFile?.optionValue ?: true
+		set(value) {
+			if (value && !optionValue) { // Ensure that an update is done if it changes from false to true, or from true to false
+				alreadyUpToDate = false
+			}
+			cachedFile?.optionValue = value
+		}
+
+	override val optionDescription get() = metadata.linkedFile?.option?.description ?: ""
+
+	init {
+		if (metadata.hashFormat?.isEmpty() != false) {
+			metadata.hashFormat = defaultFormat
+		}
+	}
+
+	fun invalidate() {
+		invalidated = true
+		alreadyUpToDate = false
+	}
+
+	fun updateFromCache(cachedFile: ManifestFile.File?) {
+		if (err != null) return
+
+		if (cachedFile == null) {
+			this.cachedFile = ManifestFile.File()
+			return
+		}
+		this.cachedFile = cachedFile
+		if (!invalidated) {
+			val currHash = try {
+				getHash(metadata.hashFormat!!, metadata.hash!!)
+			} catch (e: Exception) {
+				err = e
+				return
+			}
+			if (currHash == cachedFile.hash) { // Already up to date
+				alreadyUpToDate = true
+				metadataRequired = false
+			}
+		}
+		if (cachedFile.isOptional) {
+			// Because option selection dialog might set this task to true/false, metadata is always needed to download
+			// the file, and to show the description and name
+			metadataRequired = true
+		}
+	}
+
+	fun downloadMetadata(parentIndexFile: IndexFile, indexUri: SpaceSafeURI) {
+		if (err != null) return
+
+		if (metadataRequired) {
+			try {
+				// Retrieve the linked metadata file
+				metadata.downloadMeta(parentIndexFile, indexUri)
+			} catch (e: Exception) {
+				err = e
+				return
+			}
+			cachedFile?.let { cachedFile ->
+				val linkedFile = metadata.linkedFile
+				if (linkedFile != null) {
+					linkedFile.option?.let { opt ->
+						if (opt.optional) {
+							if (cachedFile.isOptional) {
+								// isOptional didn't change
+								newOptional = false
+							} else {
+								// isOptional false -> true, set option to it's default value
+								// TODO: preserve previous option value, somehow??
+								cachedFile.optionValue = opt.defaultValue
+							}
+						}
+					}
+					cachedFile.isOptional = isOptional
+					cachedFile.onlyOtherSide = !correctSide()
+				}
+			}
+		}
+	}
+
+	fun download(packFolder: String, indexUri: SpaceSafeURI) {
+		if (err != null) return
+
+		// Ensure it is 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()
+				}
+				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
+		if (metadata.preserve) {
+			if (destPath.toFile().exists()) {
+				return
+			}
+		}
+
+		try {
+			val hash: Hash
+			val fileHashFormat: String
+			val linkedFile = metadata.linkedFile
+
+			if (linkedFile != null) {
+				hash = linkedFile.hash
+				fileHashFormat = Objects.requireNonNull(Objects.requireNonNull(linkedFile.download)!!.hashFormat)!!
+			} else {
+				hash = metadata.getHashObj()
+				fileHashFormat = Objects.requireNonNull(metadata.hashFormat)!!
+			}
+
+			val src = metadata.getSource(indexUri)
+			val fileSource = getHasher(fileHashFormat).getHashingSource(src)
+			val data = Buffer()
+
+			// Read all the data into a buffer (very inefficient for large files! but allows rollback if hash check fails)
+			// TODO: should we instead rename the existing file, then stream straight to the file and rollback from the renamed file?
+			fileSource.buffer().use {
+				it.readAll(data)
+			}
+
+			if (fileSource.hashIsEqual(hash)) {
+				Files.createDirectories(destPath.parent)
+				Files.copy(data.inputStream(), destPath, StandardCopyOption.REPLACE_EXISTING)
+				data.clear()
+			} else {
+				// TODO: no more PRINTLN!!!!!!!!!
+				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())
+				data.readAll(sha256)
+				println("SHA256 hash value: " + sha256.hash)
+				err = Exception("Hash invalid!")
+				data.clear()
+				return
+			}
+			cachedFile?.cachedLocation?.let {
+				if (destPath != Paths.get(packFolder, it)) {
+					// Delete old file if location changes
+					try {
+						Files.delete(Paths.get(packFolder, cachedFile!!.cachedLocation))
+					} catch (e: IOException) {
+						// Continue, as it was probably already deleted?
+						// TODO: log it
+					}
+				}
+			}
+		} catch (e: Exception) {
+			err = e
+			return
+		}
+
+		// 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
+				}
+			}
+		}
+	}
+
+	companion object {
+		@JvmStatic
+		fun createTasksFromIndex(index: IndexFile, defaultFormat: String, downloadSide: UpdateManager.Options.Side): List<DownloadTask> {
+			val tasks = ArrayList<DownloadTask>()
+			for (file in Objects.requireNonNull(index.files)) {
+				tasks.add(DownloadTask(file, defaultFormat, downloadSide))
+			}
+			return tasks
+		}
+	}
+}

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

@@ -0,0 +1,127 @@
+@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 org.apache.commons.cli.DefaultParser
+import org.apache.commons.cli.Options
+import org.apache.commons.cli.ParseException
+import java.awt.EventQueue
+import java.awt.GraphicsEnvironment
+import java.net.URISyntaxException
+import javax.swing.JOptionPane
+import javax.swing.UIManager
+import kotlin.system.exitProcess
+
+@Suppress("unused")
+class Main(args: Array<String>) {
+	private fun startup(args: Array<String>) {
+		val options = Options()
+		addNonBootstrapOptions(options)
+		addBootstrapOptions(options)
+
+		val parser = DefaultParser()
+		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
+			}
+			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()
+
+		val unparsedArgs = cmd.args
+		if (unparsedArgs.size > 1) {
+			ui.handleExceptionAndExit(RuntimeException("Too many arguments specified!"))
+		} else if (unparsedArgs.isEmpty()) {
+			ui.handleExceptionAndExit(RuntimeException("URI to install from must be specified!"))
+		}
+
+		cmd.getOptionValue("title")?.also {
+			ui.setTitle(it)
+		}
+
+		val inputStateHandler = InputStateHandler()
+		ui.show(inputStateHandler)
+
+		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])
+		} catch (e: URISyntaxException) {
+			// TODO: better error message?
+			ui.handleExceptionAndExit(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)
+		}
+	}
+
+	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")
+			options.addOption(null, "pack-folder", true, "Folder to install the pack to (defaults to the JAR directory)")
+			options.addOption(null, "meta-file", true, "JSON file to store pack metadata, relative to the pack folder (defaults to packwiz.json)")
+		}
+
+		// 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")
+			options.addOption(null, "bootstrap-no-update", false, "Don't update packwiz-installer")
+			options.addOption(null, "bootstrap-main-jar", true, "Location of the packwiz-installer JAR file")
+			options.addOption("g", "no-gui", false, "Don't display a GUI to show update progress")
+			options.addOption("h", "help", false, "Display this message") // Implemented in packwiz-installer-bootstrap!
+		}
+	}
+
+	// Actual main() is in RequiresBootstrap!
+	init {
+		// Big overarching try/catch just in case everything breaks
+		try {
+			startup(args)
+		} catch (e: Exception) {
+			e.printStackTrace()
+			EventQueue.invokeLater {
+				JOptionPane.showMessageDialog(null,
+						"A fatal error occurred: \n" + e.javaClass.canonicalName + ": " + e.message,
+						"packwiz-installer", JOptionPane.ERROR_MESSAGE)
+				exitProcess(1)
+			}
+			// 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

@@ -0,0 +1,496 @@
+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.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.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 okio.buffer
+import java.io.FileNotFoundException
+import java.io.FileReader
+import java.io.FileWriter
+import java.io.IOException
+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) {
+	private var cancelled = false
+	private var cancelledStartGame = false
+	private var errorsOccurred = false
+
+	init {
+		start()
+	}
+
+	data class Options(
+			var downloadURI: SpaceSafeURI? = null,
+			var manifestFile: String = "packwiz.json", // TODO: make configurable
+			var packFolder: String = ".",
+			var side: Side = Side.CLIENT
+	) {
+		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
+				}
+			}
+		}
+	}
+
+	private fun start() {
+		checkOptions()
+
+		ui.submitProgress(InstallProgress("Loading manifest file..."))
+		val gson = GsonBuilder().registerTypeAdapter(Hash::class.java, Hash.TypeHandler()).create()
+		val manifest = try {
+			gson.fromJson(FileReader(Paths.get(opts.packFolder, opts.manifestFile).toString()),
+					ManifestFile::class.java)
+		} catch (e: FileNotFoundException) {
+			ManifestFile()
+		} catch (e: JsonSyntaxException) {
+			ui.handleExceptionAndExit(e)
+			return
+		} catch (e: JsonIOException) {
+			ui.handleExceptionAndExit(e)
+			return
+		}
+
+		if (stateHandler.cancelButton) {
+			showCancellationDialog()
+			handleCancellation()
+		}
+
+		ui.submitProgress(InstallProgress("Loading pack file..."))
+		val packFileSource = try {
+			val src = getFileSource(opts.downloadURI!!)
+			getHasher("sha256").getHashingSource(src)
+		} catch (e: Exception) {
+			// TODO: run cancellation window?
+			ui.handleExceptionAndExit(e)
+			return
+		}
+		val pf = packFileSource.buffer().use {
+			try {
+				Toml().read(it.inputStream()).to(PackFile::class.java)
+			} catch (e: IllegalStateException) {
+				ui.handleExceptionAndExit(e)
+				return
+			}
+		}
+
+		if (stateHandler.cancelButton) {
+			showCancellationDialog()
+			handleCancellation()
+		}
+
+		ui.submitProgress(InstallProgress("Checking local files..."))
+
+		// Invalidation checking must be done here, as it must happen before pack/index hashes are checked
+		val invalidatedUris: MutableList<SpaceSafeURI> = ArrayList()
+		for ((fileUri, file) in manifest.cachedFiles) {
+			// ignore onlyOtherSide files
+			if (file.onlyOtherSide) {
+				continue
+			}
+
+			var invalid = false
+			// if isn't optional, or is optional but optionValue == true
+			if (!file.isOptional || file.optionValue) {
+				if (file.cachedLocation != null) {
+					if (!Paths.get(opts.packFolder, file.cachedLocation).toFile().exists()) {
+						invalid = true
+					}
+				} else {
+					// if cachedLocation == null, should probably be installed!!
+					invalid = true
+				}
+			}
+			if (invalid) {
+				println("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) {
+				return
+			}
+		}
+
+		println("Modpack name: " + pf.name)
+
+		if (stateHandler.cancelButton) {
+			showCancellationDialog()
+			handleCancellation()
+		}
+		try {
+			val index = pf.index!!
+			getNewLoc(opts.downloadURI, index.file)?.let { newLoc ->
+				index.hashFormat?.let { hashFormat ->
+					processIndex(
+						newLoc,
+						getHash(index.hashFormat!!, index.hash!!),
+						hashFormat,
+						manifest,
+						invalidatedUris
+					)
+				}
+			}
+		} catch (e1: Exception) {
+			ui.handleExceptionAndExit(e1)
+		}
+
+		handleCancellation()
+
+		// TODO: update MMC params, java args etc
+
+		// If there were errors, don't write the manifest/index hashes, to ensure they are rechecked later
+		if (errorsOccurred) {
+			manifest.indexFileHash = null
+			manifest.packFileHash = null
+		} else {
+			manifest.packFileHash = packFileSource.hash
+		}
+
+		manifest.cachedSide = opts.side
+		try {
+			FileWriter(Paths.get(opts.packFolder, opts.manifestFile).toString()).use { writer -> gson.toJson(manifest, writer) }
+		} catch (e: IOException) {
+			// TODO: add message?
+			ui.handleException(e)
+		}
+	}
+
+	private fun checkOptions() {
+		// TODO: implement
+	}
+
+	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) {
+				return
+			}
+		}
+		manifest.indexFileHash = indexHash
+
+		val indexFileSource = try {
+			val src = getFileSource(indexUri)
+			getHasher(hashFormat).getHashingSource(src)
+		} catch (e: Exception) {
+			// TODO: run cancellation window?
+			ui.handleExceptionAndExit(e)
+			return
+		}
+		val indexFile = try {
+			Toml().read(indexFileSource.buffer().inputStream()).to(IndexFile::class.java)
+		} catch (e: IllegalStateException) {
+			ui.handleExceptionAndExit(e)
+			return
+		}
+		if (!indexFileSource.hashIsEqual(indexHash)) {
+			// TODO: throw exception
+			println("I was meant to put an error message here but I'll do that later")
+			return
+		}
+		if (stateHandler.cancelButton) {
+			showCancellationDialog()
+			return
+		}
+
+		ui.submitProgress(InstallProgress("Checking local files..."))
+		// TODO: use kotlin filtering/FP rather than an iterator?
+		val it: MutableIterator<Map.Entry<SpaceSafeURI, ManifestFile.File>> = manifest.cachedFiles.entries.iterator()
+		while (it.hasNext()) {
+			val (uri, file) = it.next()
+			if (file.cachedLocation != null) {
+				var alreadyDeleted = false
+				// Delete if option value has been set to false
+				if (file.isOptional && !file.optionValue) {
+					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()
+					}
+					// Set to null, as it doesn't exist anymore
+					file.cachedLocation = null
+					alreadyDeleted = true
+				}
+				if (indexFile.files.none { it.file == uri }) { // File has been removed from the index
+					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()
+						}
+					}
+					it.remove()
+				}
+			}
+		}
+
+		if (stateHandler.cancelButton) {
+			showCancellationDialog()
+			return
+		}
+		ui.submitProgress(InstallProgress("Comparing new files..."))
+
+		// TODO: progress bar?
+		if (indexFile.files.isEmpty()) {
+			println("Warning: 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")
+		}
+		tasks.forEach{ f ->
+			// TODO: should linkedfile be checked as well? should this be done in the download section?
+			if (invalidateAll) {
+				f.invalidate()
+			} else if (invalidatedUris.contains(f.metadata.file)) {
+				f.invalidate()
+			}
+			val file = manifest.cachedFiles[f.metadata.file]
+			// Ensure the file can be reverted later if necessary - the DownloadTask modifies the file so if it fails we need the old version back
+			file?.backup()
+			// If it is null, the DownloadTask will make a new empty cachedFile
+			f.updateFromCache(file)
+		}
+
+		if (stateHandler.cancelButton) {
+			showCancellationDialog()
+			return
+		}
+
+		// Let's hope downloadMetadata is a pure function!!!
+		tasks.parallelStream().forEach { f -> f.downloadMetadata(indexFile, indexUri) }
+
+		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) {
+				ExceptionListResult.CONTINUE -> {}
+				ExceptionListResult.CANCEL -> {
+					cancelled = true
+					return
+				}
+				ExceptionListResult.IGNORE -> {
+					cancelledStartGame = true
+					return
+				}
+			}
+		}
+
+		if (stateHandler.cancelButton) {
+			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??
+					return
+				}
+			} catch (e: InterruptedException) {
+				// Interrupted means cancelled???
+				ui.handleExceptionAndExit(e)
+			} catch (e: ExecutionException) {
+				ui.handleExceptionAndExit(e)
+			}
+		}
+		ui.disableOptionsButton()
+
+		// TODO: different thread pool type?
+		val threadPool = Executors.newFixedThreadPool(10)
+		val completionService: CompletionService<DownloadTask> = ExecutorCompletionService(threadPool)
+		tasks.forEach { t ->
+			completionService.submit {
+				t.download(opts.packFolder, indexUri)
+				t
+			}
+		}
+		for (i in tasks.indices) {
+			var task: DownloadTask?
+			task = try {
+				completionService.take().get()
+			} catch (e: InterruptedException) {
+				ui.handleException(e)
+				null
+			} catch (e: ExecutionException) {
+				ui.handleException(e)
+				null
+			}
+			// Update manifest - If there were no errors cachedFile has already been modified in place (good old pass by reference)
+			task?.cachedFile?.let { file ->
+				if (task.failed()) {
+					val oldFile = file.revert
+					if (oldFile != null) {
+						task.metadata.file?.let { uri -> manifest.cachedFiles.putIfAbsent(uri, oldFile) }
+					} else { null }
+				} else {
+					task.metadata.file?.let { uri -> manifest.cachedFiles.putIfAbsent(uri, file) }
+				}
+			}
+
+			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}"
+				}
+			} else {
+				progress = "Failed to download, unknown reason"
+			}
+			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!)
+				threadPool.shutdown()
+				cancelled = true
+				return
+			}
+		}
+
+		// Shut down the thread pool when the update is done
+		threadPool.shutdown()
+
+		val failedTasks2ElectricBoogaloo = nonFailedFirstTasks.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) {
+				ExceptionListResult.CONTINUE -> {}
+				ExceptionListResult.CANCEL -> cancelled = true
+				ExceptionListResult.IGNORE -> cancelledStartGame = true
+			}
+		}
+	}
+
+	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
+		}
+		when (cancellationResult) {
+			CancellationResult.QUIT -> cancelled = true
+			CancellationResult.CONTINUE -> cancelledStartGame = true
+		}
+	}
+
+	private fun handleCancellation() {
+		if (cancelled) {
+			println("Update cancelled by user!")
+			exitProcess(1)
+		} else if (cancelledStartGame) {
+			println("Update cancelled by user! Continuing to start game...")
+			exitProcess(0)
+		}
+	}
+}

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

@@ -0,0 +1,27 @@
+package link.infra.packwiz.installer.metadata
+
+import com.google.gson.TypeAdapter
+import com.google.gson.stream.JsonReader
+import com.google.gson.stream.JsonToken
+import com.google.gson.stream.JsonWriter
+import java.io.IOException
+
+class EfficientBooleanAdapter : TypeAdapter<Boolean?>() {
+	@Throws(IOException::class)
+	override fun write(out: JsonWriter, value: Boolean?) {
+		if (value == null || !value) {
+			out.nullValue()
+			return
+		}
+		out.value(true)
+	}
+
+	@Throws(IOException::class)
+	override fun read(reader: JsonReader): Boolean? {
+		if (reader.peek() == JsonToken.NULL) {
+			reader.nextNull()
+			return false
+		}
+		return reader.nextBoolean()
+	}
+}

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

@@ -0,0 +1,99 @@
+package link.infra.packwiz.installer.metadata
+
+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.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 okio.Source
+import okio.buffer
+import java.nio.file.Paths
+
+class IndexFile {
+	@SerializedName("hash-format")
+	var hashFormat: String = "sha-256"
+	var files: MutableList<File> = ArrayList()
+
+	class File {
+		var file: SpaceSafeURI? = null
+		@SerializedName("hash-format")
+		var hashFormat: String? = null
+		var hash: String? = null
+		var alias: SpaceSafeURI? = null
+		var metafile = false
+		var preserve = false
+
+		@Transient
+		var linkedFile: ModFile? = null
+		@Transient
+		var linkedFileURI: SpaceSafeURI? = null
+
+		@Throws(Exception::class)
+		fun downloadMeta(parentIndexFile: IndexFile, indexUri: SpaceSafeURI?) {
+			if (!metafile) {
+				return
+			}
+			if (hashFormat?.length ?: 0 == 0) {
+				hashFormat = parentIndexFile.hashFormat
+			}
+			// TODO: throw a proper exception instead of allowing NPE?
+			val fileHash = getHash(hashFormat!!, hash!!)
+			linkedFileURI = getNewLoc(indexUri, file)
+			val src = getFileSource(linkedFileURI!!)
+			val fileStream = getHasher(hashFormat!!).getHashingSource(src)
+			linkedFile = Toml().read(fileStream.buffer().inputStream()).to(ModFile::class.java)
+			if (!fileStream.hashIsEqual(fileHash)) {
+				throw Exception("Invalid mod file hash")
+			}
+		}
+
+		@Throws(Exception::class)
+		fun getSource(indexUri: SpaceSafeURI?): Source {
+			return if (metafile) {
+				if (linkedFile == null) {
+					throw Exception("Linked file doesn't exist!")
+				}
+				linkedFile!!.getSource(linkedFileURI)
+			} else {
+				val newLoc = getNewLoc(indexUri, file) ?: throw Exception("Index file URI is invalid")
+				getFileSource(newLoc)
+			}
+		}
+
+		@Throws(Exception::class)
+		fun getHashObj(): Hash {
+			if (hash == null) { // TODO: should these be more specific exceptions (e.g. IndexFileException?!)
+				throw Exception("Index file doesn't have a hash")
+			}
+			if (hashFormat == null) {
+				throw Exception("Index file doesn't have a hash format")
+			}
+			return getHash(hashFormat!!, hash!!)
+		}
+
+		// TODO: throw some kind of exception?
+		val name: String
+			get() {
+				if (metafile) {
+					return linkedFile?.name ?: linkedFile?.filename ?:
+					file?.run { Paths.get(path).fileName.toString() } ?: "Invalid file"
+				}
+				return file?.run { Paths.get(path).fileName.toString() } ?: "Invalid file"
+			}
+
+		// TODO: URIs are bad
+		val destURI: SpaceSafeURI?
+			get() {
+				if (alias != null) {
+					return alias
+				}
+				return if (metafile && linkedFile != null) {
+					linkedFile?.filename?.let { file?.resolve(it) }
+				} else {
+					file
+				}
+			}
+	}
+}

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

@@ -0,0 +1,44 @@
+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
+
+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
+
+	// TODO: switch to Kotlin-friendly JSON/TOML libs?
+	class File {
+		@Transient
+		var revert: File? = null
+			private set
+
+		var hash: Hash? = null
+		var linkedFileHash: Hash? = null
+		var cachedLocation: String? = null
+
+		@JsonAdapter(EfficientBooleanAdapter::class)
+		var isOptional = false
+		var optionValue = true
+
+		@JsonAdapter(EfficientBooleanAdapter::class)
+		var onlyOtherSide = false
+
+		// When an error occurs, the state needs to be reverted. To do this, I have a crude revert system.
+		fun backup() {
+			revert = File().also {
+				it.hash = hash
+				it.linkedFileHash = linkedFileHash
+				it.cachedLocation = cachedLocation
+				it.isOptional = isOptional
+				it.optionValue = optionValue
+				it.onlyOtherSide = onlyOtherSide
+			}
+		}
+
+	}
+}

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

@@ -0,0 +1,57 @@
+package link.infra.packwiz.installer.metadata
+
+import com.google.gson.annotations.SerializedName
+import link.infra.packwiz.installer.UpdateManager
+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 okio.Source
+
+class ModFile {
+	var name: String? = null
+	var filename: String? = null
+	var side: UpdateManager.Options.Side? = null
+	var download: Download? = null
+
+	class Download {
+		var url: SpaceSafeURI? = null
+		@SerializedName("hash-format")
+		var hashFormat: String? = null
+		var hash: String? = null
+	}
+
+	var update: Map<String, Any>? = null
+	var option: Option? = null
+
+	class Option {
+		var optional = false
+		var description: String? = null
+		@SerializedName("default")
+		var defaultValue = false
+	}
+
+	@Throws(Exception::class)
+	fun getSource(baseLoc: SpaceSafeURI?): Source {
+		download?.let {
+			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)
+		} ?: throw Exception("Metadata file doesn't have download")
+	}
+
+	@get:Throws(Exception::class)
+	val hash: Hash
+		get() {
+			download?.let {
+				return getHash(
+						it.hashFormat ?: throw Exception("Metadata file doesn't have a hash format"),
+						it.hash ?: throw Exception("Metadata file doesn't have a hash")
+				)
+			} ?: throw Exception("Metadata file doesn't have download")
+		}
+
+	val isOptional: Boolean get() = option?.optional ?: false
+}

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

@@ -0,0 +1,19 @@
+package link.infra.packwiz.installer.metadata
+
+import com.google.gson.annotations.SerializedName
+
+class PackFile {
+	var name: String? = null
+	var index: IndexFileLoc? = null
+
+	class IndexFileLoc {
+		var file: SpaceSafeURI? = null
+		@SerializedName("hash-format")
+		var hashFormat: String? = null
+		var hash: String? = null
+	}
+
+	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

@@ -0,0 +1,61 @@
+package link.infra.packwiz.installer.metadata
+
+import com.google.gson.annotations.JsonAdapter
+import java.io.Serializable
+import java.net.MalformedURLException
+import java.net.URI
+import java.net.URISyntaxException
+import java.net.URL
+
+// The world's worst URI wrapper
+@JsonAdapter(SpaceSafeURIParser::class)
+class SpaceSafeURI : Comparable<SpaceSafeURI>, Serializable {
+	private val u: URI
+
+	@Throws(URISyntaxException::class)
+	constructor(str: String) {
+		u = URI(str.replace(" ", "%20"))
+	}
+
+	constructor(uri: URI) {
+		u = uri
+	}
+
+	@Throws(URISyntaxException::class)
+	constructor(scheme: String?, authority: String?, path: String?, query: String?, fragment: String?) { // TODO: do all components need to be replaced?
+		u = URI(
+				scheme?.replace(" ", "%20"),
+				authority?.replace(" ", "%20"),
+				path?.replace(" ", "%20"),
+				query?.replace(" ", "%20"),
+				fragment?.replace(" ", "%20")
+		)
+	}
+
+	val path: String get() = u.path.replace("%20", " ")
+
+	override fun toString(): String = u.toString().replace("%20", " ")
+
+	fun resolve(path: String): SpaceSafeURI = SpaceSafeURI(u.resolve(path.replace(" ", "%20")))
+
+	fun resolve(loc: SpaceSafeURI): SpaceSafeURI = SpaceSafeURI(u.resolve(loc.u))
+
+	fun relativize(loc: SpaceSafeURI): SpaceSafeURI = SpaceSafeURI(u.relativize(loc.u))
+
+	override fun equals(other: Any?): Boolean {
+		return if (other is SpaceSafeURI) {
+			u == other.u
+		} else false
+	}
+
+	override fun hashCode() = u.hashCode()
+
+	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
+
+	@Throws(MalformedURLException::class)
+	fun toURL(): URL = u.toURL()
+}

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

@@ -0,0 +1,25 @@
+package link.infra.packwiz.installer.metadata
+
+import com.google.gson.JsonDeserializationContext
+import com.google.gson.JsonDeserializer
+import com.google.gson.JsonElement
+import com.google.gson.JsonParseException
+import java.lang.reflect.Type
+import java.net.URISyntaxException
+
+/**
+ * This class encodes spaces before parsing the URI, so the URI can actually be
+ * parsed.
+ */
+internal class SpaceSafeURIParser : JsonDeserializer<SpaceSafeURI> {
+	@Throws(JsonParseException::class)
+	override fun deserialize(json: JsonElement, typeOfT: Type, context: JsonDeserializationContext): SpaceSafeURI {
+		return try {
+			SpaceSafeURI(json.asString)
+		} catch (e: URISyntaxException) {
+			throw JsonParseException("Failed to parse URI", e)
+		}
+	}
+
+	// TODO: replace this with a better solution?
+}

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

@@ -0,0 +1,10 @@
+package link.infra.packwiz.installer.metadata.hash
+
+import okio.ForwardingSource
+import okio.Source
+
+abstract class GeneralHashingSource(delegate: Source) : ForwardingSource(delegate) {
+	abstract val hash: Hash
+
+	fun hashIsEqual(compareTo: Any) = compareTo == hash
+}

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

@@ -0,0 +1,34 @@
+package link.infra.packwiz.installer.metadata.hash
+
+import com.google.gson.*
+import java.lang.reflect.Type
+
+abstract class Hash {
+	protected abstract val stringValue: String
+	protected abstract val type: String
+
+	class TypeHandler : JsonDeserializer<Hash>, JsonSerializer<Hash> {
+		override fun serialize(src: Hash, typeOfSrc: Type, context: JsonSerializationContext): JsonElement = JsonObject().apply {
+			add("type", JsonPrimitive(src.type))
+			add("value", JsonPrimitive(src.stringValue))
+		}
+
+		@Throws(JsonParseException::class)
+		override fun deserialize(json: JsonElement, typeOfT: Type, context: JsonDeserializationContext): Hash {
+			val obj = json.asJsonObject
+			val type: String
+			val value: String
+			try {
+				type = obj["type"].asString
+				value = obj["value"].asString
+			} catch (e: NullPointerException) {
+				throw JsonParseException("Invalid hash JSON data")
+			}
+			return try {
+				HashUtils.getHash(type, value)
+			} catch (e: Exception) {
+				throw JsonParseException("Failed to create hash object", e)
+			}
+		}
+	}
+}

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

@@ -0,0 +1,21 @@
+package link.infra.packwiz.installer.metadata.hash
+
+object HashUtils {
+	private val hashTypeConversion: Map<String, IHasher> = mapOf(
+			"sha256" to HashingSourceHasher("sha256"),
+			"sha512" to HashingSourceHasher("sha512"),
+			"murmur2" to Murmur2Hasher()
+	)
+
+	@JvmStatic
+	@Throws(Exception::class)
+	fun getHasher(type: String): IHasher {
+		return hashTypeConversion[type] ?: throw Exception("Hash type not supported: $type")
+	}
+
+	@JvmStatic
+	@Throws(Exception::class)
+	fun getHash(type: String, value: String): Hash {
+		return hashTypeConversion[type]?.getHash(value) ?: throw Exception("Hash type not supported: $type")
+	}
+}

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

@@ -0,0 +1,45 @@
+package link.infra.packwiz.installer.metadata.hash
+
+import okio.HashingSource
+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) {
+		override val hash: Hash by lazy(LazyThreadSafetyMode.NONE) {
+			HashingSourceHash(delegateHashing.hash.hex())
+		}
+	}
+
+	// this some funky inner class stuff
+	// each of these classes is specific to the instance of the HasherHashingSource
+	// therefore HashingSourceHashes from different parent instances will be not instanceof each other
+	private inner class HashingSourceHash(val value: String) : Hash() {
+		override val stringValue get() = value
+
+		override fun equals(other: Any?): Boolean {
+			if (other !is HashingSourceHash) {
+				return false
+			}
+			return stringValue.equals(other.stringValue, ignoreCase = true)
+		}
+
+		override fun toString(): String = "$type: $stringValue"
+		override fun hashCode(): Int = value.hashCode()
+
+		override val type: String get() = this@HashingSourceHasher.type
+	}
+
+	override fun getHashingSource(delegate: Source): GeneralHashingSource {
+		when (type) {
+			"md5" -> return HashingSourceGeneralHashingSource(HashingSource.md5(delegate))
+			"sha256" -> return HashingSourceGeneralHashingSource(HashingSource.sha256(delegate))
+			"sha512" -> return HashingSourceGeneralHashingSource(HashingSource.sha512(delegate))
+		}
+		throw RuntimeException("Invalid hash type provided")
+	}
+
+	override fun getHash(value: String): Hash {
+		return HashingSourceHash(value)
+	}
+}

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

@@ -0,0 +1,8 @@
+package link.infra.packwiz.installer.metadata.hash
+
+import okio.Source
+
+interface IHasher {
+	fun getHashingSource(delegate: Source): GeneralHashingSource
+	fun getHash(value: String): Hash
+}

src/main/kotlin/link/infra/packwiz/installer/metadata/hash/Murmur2Hasher.kt

@@ -0,0 +1,91 @@
+package link.infra.packwiz.installer.metadata.hash
+
+import okio.Buffer
+import okio.Source
+import java.io.IOException
+
+class Murmur2Hasher : IHasher {
+	private inner class Murmur2GeneralHashingSource(delegate: Source) : GeneralHashingSource(delegate) {
+		val internalBuffer = Buffer()
+		val tempBuffer = Buffer()
+
+		override val hash: Hash by lazy(LazyThreadSafetyMode.NONE) {
+			val data = internalBuffer.readByteArray()
+			Murmur2Hash(Murmur2Lib.hash32(data, data.size, 1))
+		}
+
+		@Throws(IOException::class)
+		override fun read(sink: Buffer, byteCount: Long): Long {
+			val out = delegate.read(tempBuffer, byteCount)
+			if (out > -1) {
+				sink.write(tempBuffer.clone(), out)
+				computeNormalizedBufferFaster(tempBuffer, internalBuffer)
+			}
+			return out
+		}
+
+		// Credit to https://github.com/modmuss50/CAV2/blob/master/murmur.go
+//		private fun computeNormalizedArray(input: ByteArray): ByteArray {
+//			val output = ByteArray(input.size)
+//			var index = 0
+//			for (b in input) {
+//				when (b) {
+//					9.toByte(), 10.toByte(), 13.toByte(), 32.toByte() -> {}
+//					else -> {
+//						output[index] = b
+//						index++
+//					}
+//				}
+//			}
+//			val outputTrimmed = ByteArray(index)
+//			System.arraycopy(output, 0, outputTrimmed, 0, index)
+//			return outputTrimmed
+//		}
+
+		private fun computeNormalizedBufferFaster(input: Buffer, output: Buffer) {
+			var index = 0
+			val arr = input.readByteArray()
+			for (b in arr) {
+				when (b) {
+					9.toByte(), 10.toByte(), 13.toByte(), 32.toByte() -> {}
+					else -> {
+						arr[index] = b
+						index++
+					}
+				}
+			}
+			output.write(arr, 0, index)
+		}
+
+	}
+
+	private class Murmur2Hash : Hash {
+		val value: Int
+
+		constructor(value: String) {
+			// Parsing as long then casting to int converts values gt int max value but lt uint max value
+			// into negatives. I presume this is how the murmur2 code handles this.
+			this.value = value.toLong().toInt()
+		}
+
+		constructor(value: Int) {
+			this.value = value
+		}
+
+		override val stringValue get() = value.toString()
+		override val type get() = "murmur2"
+
+		override fun equals(other: Any?): Boolean {
+			if (other !is Murmur2Hash) {
+				return false
+			}
+			return value == other.value
+		}
+
+		override fun toString(): String = "murmur2: $value"
+		override fun hashCode(): Int = value
+	}
+
+	override fun getHashingSource(delegate: Source): GeneralHashingSource = Murmur2GeneralHashingSource(delegate)
+	override fun getHash(value: String): Hash = Murmur2Hash(value)
+}

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

@@ -0,0 +1,49 @@
+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
+
+object HandlerManager {
+
+	private val handlers: List<IRequestHandler> = listOf(
+			RequestHandlerGithub(),
+			RequestHandlerHTTP(),
+			RequestHandlerFile()
+	)
+
+	@JvmStatic
+	fun getNewLoc(base: SpaceSafeURI?, loc: SpaceSafeURI?): SpaceSafeURI? {
+		if (loc == null) {
+			return null
+		}
+		val dest = base?.run { resolve(loc) } ?: loc
+		for (handler in handlers) with (handler) {
+			if (matchesHandler(dest)) {
+				return getNewLoc(dest)
+			}
+		}
+		return dest
+	}
+
+	// TODO: What if files are read multiple times??
+	// Zip handler discards once read, requesting multiple times on other handlers would cause multiple downloads
+	// Caching system? Copy from already downloaded files?
+
+	@JvmStatic
+	@Throws(Exception::class)
+	fun getFileSource(loc: SpaceSafeURI): Source {
+		for (handler in handlers) {
+			if (handler.matchesHandler(loc)) {
+				return handler.getFileSource(loc) ?: throw Exception("Couldn't find URI: $loc")
+			}
+		}
+		throw Exception("No handler available for URI: $loc")
+	}
+
+	// TODO: github toml resolution?
+	// e.g. https://github.com/comp500/Demagnetize -> demagnetize.toml
+	// https://github.com/comp500/Demagnetize/blob/master/demagnetize.toml
+}

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

@@ -0,0 +1,24 @@
+package link.infra.packwiz.installer.request
+
+import link.infra.packwiz.installer.metadata.SpaceSafeURI
+import okio.Source
+
+/**
+ * IRequestHandler handles requests for locations specified in modpack metadata.
+ */
+interface IRequestHandler {
+	fun matchesHandler(loc: SpaceSafeURI): Boolean
+
+	fun getNewLoc(loc: SpaceSafeURI): SpaceSafeURI {
+		return loc
+	}
+
+	/**
+	 * Gets the Source for a location. Must be threadsafe.
+	 * It is assumed that each location is read only once for the duration of an IRequestHandler.
+	 * @param loc The location to be read
+	 * @return The Source containing the data of the file
+	 * @throws Exception Exception if it failed to download a file!!!
+	 */
+	fun getFileSource(loc: SpaceSafeURI): Source?
+}

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

@@ -0,0 +1,71 @@
+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
+import kotlin.concurrent.write
+
+class RequestHandlerGithub : RequestHandlerZip(true) {
+	override fun getNewLoc(loc: SpaceSafeURI): SpaceSafeURI {
+		return loc
+	}
+
+	companion object {
+		private val repoMatcherPattern = Pattern.compile("/([\\w.-]+/[\\w.-]+).*")
+		private val branchMatcherPattern = Pattern.compile("/[\\w.-]+/[\\w.-]+/blob/([\\w.-]+).*")
+	}
+
+	// TODO: is caching really needed, if HTTPURLConnection follows redirects correctly?
+	private val zipUriMap: MutableMap<String, SpaceSafeURI> = HashMap()
+	private val zipUriLock = ReentrantReadWriteLock()
+	private fun getRepoName(loc: SpaceSafeURI): String? {
+		val matcher = repoMatcherPattern.matcher(loc.path)
+		return if (matcher.matches()) {
+			matcher.group(1)
+		} else {
+			null
+		}
+	}
+
+	override fun getZipUri(loc: SpaceSafeURI): SpaceSafeURI {
+		val repoName = getRepoName(loc)
+		val branchName = getBranch(loc)
+
+		zipUriLock.read {
+			zipUriMap["$repoName/$branchName"]
+		}?.let { return it }
+
+		var zipUri = SpaceSafeURI("https://api.github.com/repos/$repoName/zipball/$branchName")
+		zipUriLock.write {
+			// If another thread sets the value concurrently, use the existing value from the
+			// thread that first acquired the lock.
+			zipUri = zipUriMap.putIfAbsent("$repoName/$branchName", zipUri) ?: zipUri
+		}
+		return zipUri
+	}
+
+	private fun getBranch(loc: SpaceSafeURI): String? {
+		val matcher = branchMatcherPattern.matcher(loc.path)
+		return if (matcher.matches()) {
+			matcher.group(1)
+		} else {
+			null
+		}
+	}
+
+	override fun getLocationInZip(loc: SpaceSafeURI): SpaceSafeURI {
+		val path = "/" + getRepoName(loc) + "/blob/" + getBranch(loc)
+		return SpaceSafeURI(loc.scheme, loc.authority, path, null, null).relativize(loc)
+	}
+
+	override fun matchesHandler(loc: SpaceSafeURI): Boolean {
+		val scheme = loc.scheme
+		if (!("http" == scheme || "https" == scheme)) {
+			return false
+		}
+		return "github.com" == loc.host
+		// TODO: sanity checks, support for more github urls
+	}
+}

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

@@ -0,0 +1,25 @@
+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
+
+open class RequestHandlerHTTP : IRequestHandler {
+	override fun matchesHandler(loc: SpaceSafeURI): Boolean {
+		val scheme = loc.scheme
+		return "http" == scheme || "https" == scheme
+	}
+
+	override fun getFileSource(loc: SpaceSafeURI): Source? {
+		val conn = loc.toURL().openConnection()
+		// 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.apply {
+			// 30 second read timeout
+			readTimeout = 30 * 1000
+		}
+		return conn.getInputStream().source()
+	}
+}

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

@@ -0,0 +1,123 @@
+package link.infra.packwiz.installer.request.handlers
+
+import link.infra.packwiz.installer.metadata.SpaceSafeURI
+import okio.Buffer
+import okio.Source
+import okio.buffer
+import okio.source
+import java.util.*
+import java.util.concurrent.locks.ReentrantLock
+import java.util.concurrent.locks.ReentrantReadWriteLock
+import java.util.function.Predicate
+import java.util.zip.ZipEntry
+import java.util.zip.ZipInputStream
+import kotlin.concurrent.read
+import kotlin.concurrent.withLock
+import kotlin.concurrent.write
+
+abstract class RequestHandlerZip(private val modeHasFolder: Boolean) : RequestHandlerHTTP() {
+	private fun removeFolder(name: String): String {
+		return if (modeHasFolder) {
+			// TODO: replace with proper path checks once switched to Path??
+			name.substring(name.indexOf("/") + 1)
+		} else {
+			name
+		}
+	}
+
+	private inner class ZipReader internal constructor(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!
+		val filesLock = ReentrantLock()
+		private var entry: ZipEntry? = null
+
+		private val zipSource = zis.source().buffer()
+
+		// File lock must be obtained before calling this function
+		private fun readCurrFile(): Buffer {
+			val fileBuffer = Buffer()
+			zipSource.readFully(fileBuffer, entry!!.size)
+			return fileBuffer
+		}
+
+		// File lock must be obtained before calling this function
+		private fun findFile(loc: SpaceSafeURI): Buffer? {
+			while (true) {
+				entry = zis.nextEntry
+				entry?.also {
+					val data = readCurrFile()
+					val fileLoc = SpaceSafeURI(removeFolder(it.name))
+					if (loc == fileLoc) {
+						return data
+					} else {
+						readFiles[fileLoc] = data
+					}
+				} ?: return null
+			}
+		}
+
+		fun getFileSource(loc: SpaceSafeURI): Source? {
+			filesLock.withLock {
+				// Assume files are only read once, allow GC by removing
+				readFiles.remove(loc)?.also { return it }
+				return findFile(loc)
+			}
+		}
+
+		fun findInZip(matches: Predicate<SpaceSafeURI>): SpaceSafeURI? {
+			filesLock.withLock {
+				readFiles.keys.find { matches.test(it) }?.let { return it }
+
+				do {
+					val entry = zis.nextEntry?.also {
+						val data = readCurrFile()
+						val fileLoc = SpaceSafeURI(removeFolder(it.name))
+						readFiles[fileLoc] = data
+						if (matches.test(fileLoc)) {
+							return fileLoc
+						}
+					}
+				} while (entry != null)
+				return null
+			}
+		}
+	}
+
+	private val cache: MutableMap<SpaceSafeURI, ZipReader> = HashMap()
+	private val cacheLock = ReentrantReadWriteLock()
+
+	protected abstract fun getZipUri(loc: SpaceSafeURI): SpaceSafeURI
+	protected abstract fun getLocationInZip(loc: SpaceSafeURI): SpaceSafeURI
+	abstract override fun matchesHandler(loc: SpaceSafeURI): Boolean
+
+	override fun getFileSource(loc: SpaceSafeURI): Source? {
+		val zipUri = getZipUri(loc)
+		var zr = cacheLock.read { cache[zipUri] }
+		if (zr == null) {
+			cacheLock.write {
+				// Recheck, because unlocking read lock allows another thread to modify it
+				zr = cache[zipUri]
+
+				if (zr == null) {
+					val src = super.getFileSource(zipUri) ?: return null
+					zr = ZipReader(src).also { cache[zipUri] = it }
+				}
+			}
+		}
+		return zr?.getFileSource(getLocationInZip(loc))
+	}
+
+	protected fun findInZip(loc: SpaceSafeURI, matches: Predicate<SpaceSafeURI>): SpaceSafeURI? {
+		val zipUri = getZipUri(loc)
+		return (cacheLock.read { cache[zipUri] } ?: cacheLock.write {
+			// Recheck, because unlocking read lock allows another thread to modify it
+			cache[zipUri] ?: run {
+				// Create the ZipReader if it doesn't exist, return null if getFileSource returns null
+				super.getFileSource(zipUri)?.let { ZipReader(it) }
+						?.also { cache[zipUri] = it }
+			}
+		})?.findInZip(matches)
+	}
+
+}

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

@@ -0,0 +1,47 @@
+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/ExceptionDetails.kt

@@ -0,0 +1,6 @@
+package link.infra.packwiz.installer.ui
+
+data class ExceptionDetails(
+		val name: String,
+		val exception: Exception
+)

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

@@ -0,0 +1,151 @@
+package link.infra.packwiz.installer.ui
+
+import java.awt.BorderLayout
+import java.awt.Desktop
+import java.awt.event.WindowAdapter
+import java.awt.event.WindowEvent
+import java.io.IOException
+import java.io.PrintWriter
+import java.io.StringWriter
+import java.net.URI
+import java.net.URISyntaxException
+import java.util.concurrent.CompletableFuture
+import javax.swing.*
+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>() {
+		override fun getSize() = details.size
+		override fun getElementAt(index: Int) = details[index].name
+		fun getExceptionAt(index: Int) = details[index].exception
+	}
+
+	/**
+	 * Create the dialog.
+	 */
+	init {
+		setBounds(100, 100, 540, 340)
+		setLocationRelativeTo(parentWindow)
+
+		contentPane.apply {
+			layout = BorderLayout()
+
+			// Error panel
+			add(JPanel().apply {
+				add(JLabel("One or more errors were encountered while installing the modpack!").apply {
+					icon = UIManager.getIcon("OptionPane.warningIcon")
+				})
+			}, BorderLayout.NORTH)
+
+			// Content panel
+			add(JPanel().apply {
+				border = EmptyBorder(5, 5, 5, 5)
+				layout = BorderLayout(0, 0)
+
+				add(JSplitPane().apply {
+					resizeWeight = 0.3
+
+					lblExceptionStacktrace = JTextArea("Select a file")
+					lblExceptionStacktrace.background = UIManager.getColor("List.background")
+					lblExceptionStacktrace.isOpaque = true
+					lblExceptionStacktrace.wrapStyleWord = true
+					lblExceptionStacktrace.lineWrap = true
+					lblExceptionStacktrace.isEditable = false
+					lblExceptionStacktrace.isFocusable = true
+					lblExceptionStacktrace.font = UIManager.getFont("Label.font")
+					lblExceptionStacktrace.border = EmptyBorder(5, 5, 5, 5)
+
+					rightComponent = JScrollPane(lblExceptionStacktrace)
+
+					leftComponent = JScrollPane(JList<String>().apply {
+						selectionMode = ListSelectionModel.SINGLE_SELECTION
+						border = EmptyBorder(5, 5, 5, 5)
+						val listModel = ExceptionListModel(eList)
+						model = listModel
+						addListSelectionListener {
+							val i = selectedIndex
+							if (i > -1) {
+								val sw = StringWriter()
+								listModel.getExceptionAt(i).printStackTrace(PrintWriter(sw))
+								lblExceptionStacktrace.text = sw.toString()
+								// Scroll to the top
+								lblExceptionStacktrace.caretPosition = 0
+							} else {
+								lblExceptionStacktrace.text = "Select a file"
+							}
+						}
+					})
+				})
+			}, BorderLayout.CENTER)
+
+			// Button pane
+			add(JPanel().apply {
+				layout = BorderLayout(0, 0)
+
+				// Right buttons
+				add(JPanel().apply {
+					add(JButton("Continue").apply {
+						toolTipText = "Attempt to continue installing, excluding the failed downloads"
+						addActionListener {
+							future.complete(IUserInterface.ExceptionListResult.CONTINUE)
+							this@ExceptionListWindow.dispose()
+						}
+					})
+
+					add(JButton("Cancel launch").apply {
+						toolTipText = "Stop launching the game"
+						addActionListener {
+							future.complete(IUserInterface.ExceptionListResult.CANCEL)
+							this@ExceptionListWindow.dispose()
+						}
+					})
+
+					add(JButton("Ignore update").apply {
+						toolTipText = "Start the game without attempting to update"
+						isEnabled = allowsIgnore
+						addActionListener {
+							future.complete(IUserInterface.ExceptionListResult.IGNORE)
+							this@ExceptionListWindow.dispose()
+						}
+					})
+				}, BorderLayout.EAST)
+
+				// Errored label
+				add(JLabel(eList.size.toString() + "/" + numTotal + " errored").apply {
+					horizontalAlignment = SwingConstants.CENTER
+				}, BorderLayout.CENTER)
+
+				// Left buttons
+				add(JPanel().apply {
+					add(JButton("Report issue").apply {
+						if (Desktop.isDesktopSupported() && Desktop.getDesktop().isSupported(Desktop.Action.BROWSE)) {
+							addActionListener {
+								try {
+									Desktop.getDesktop().browse(URI("https://github.com/comp500/packwiz-installer/issues/new"))
+								} catch (e: IOException) {
+									// lol the button just won't work i guess
+								} catch (e: URISyntaxException) {}
+							}
+						} else {
+							isEnabled = false
+						}
+					})
+				}, BorderLayout.WEST)
+			}, BorderLayout.SOUTH)
+		}
+
+		addWindowListener(object : WindowAdapter() {
+			override fun windowClosing(e: WindowEvent) {
+				future.complete(IUserInterface.ExceptionListResult.CANCEL)
+			}
+
+			override fun windowClosed(e: WindowEvent) {
+				// Just in case closing didn't get triggered - if something else called dispose() the
+				// future will have already completed
+				future.complete(IUserInterface.ExceptionListResult.CANCEL)
+			}
+		})
+	}
+}

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

@@ -0,0 +1,7 @@
+package link.infra.packwiz.installer.ui
+
+interface IOptionDetails {
+	val name: String
+	var optionValue: Boolean
+	val optionDescription: String
+}

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

@@ -0,0 +1,41 @@
+package link.infra.packwiz.installer.ui
+
+import java.util.concurrent.CompletableFuture
+import java.util.concurrent.Future
+import kotlin.system.exitProcess
+
+interface IUserInterface {
+	fun show(handler: InputStateHandler)
+	fun handleException(e: Exception)
+	@JvmDefault
+	fun handleExceptionAndExit(e: Exception) {
+		handleException(e)
+		exitProcess(1)
+	}
+
+	@JvmDefault
+	fun setTitle(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 showExceptions(exceptions: List<ExceptionDetails>, numTotal: Int, allowsIgnore: Boolean): Future<ExceptionListResult>
+	@JvmDefault
+	fun disableOptionsButton() {}
+
+	@JvmDefault
+	fun showCancellationDialog(): Future<CancellationResult> {
+		return CompletableFuture<CancellationResult>().apply {
+			complete(CancellationResult.QUIT)
+		}
+	}
+
+	enum class ExceptionListResult {
+		CONTINUE, CANCEL, IGNORE
+	}
+
+	enum class CancellationResult {
+		QUIT, CONTINUE
+	}
+}

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

@@ -0,0 +1,21 @@
+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/InstallProgress.kt

@@ -0,0 +1,12 @@
+package link.infra.packwiz.installer.ui
+
+data class InstallProgress(
+		val message: String,
+		val hasProgress: Boolean = false,
+		val progress: Int = 0,
+		val progressTotal: Int = 0
+) {
+	constructor(message: String, progress: Int, progressTotal: Int) : this(message, true, progress, progressTotal)
+
+	constructor(message: String) : this(message, false)
+}

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

@@ -0,0 +1,219 @@
+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/OptionTempHandler.kt

@@ -0,0 +1,13 @@
+package link.infra.packwiz.installer.ui
+
+// Serves as a proxy for IOptionDetails, so that setOptionValue isn't called until OK is clicked
+internal class OptionTempHandler(private val opt: IOptionDetails) : IOptionDetails {
+	override var optionValue = opt.optionValue
+
+	override val name get() = opt.name
+	override val optionDescription get() = opt.optionDescription
+
+	fun finalise() {
+		opt.optionValue = optionValue
+	}
+}

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

@@ -0,0 +1,166 @@
+package link.infra.packwiz.installer.ui
+
+import java.awt.BorderLayout
+import java.awt.FlowLayout
+import java.awt.event.ActionEvent
+import java.awt.event.ActionListener
+import java.awt.event.WindowAdapter
+import java.awt.event.WindowEvent
+import java.util.*
+import java.util.concurrent.CompletableFuture
+import javax.swing.*
+import javax.swing.border.EmptyBorder
+import javax.swing.event.TableModelListener
+import javax.swing.table.TableModel
+
+class OptionsSelectWindow internal constructor(optList: List<IOptionDetails>, future: CompletableFuture<Boolean>, parentWindow: JFrame?) : JDialog(parentWindow, "Select optional mods...", true), ActionListener {
+	private val lblOptionDescription: JTextArea
+	private val tableModel: OptionTableModel
+	private val future: CompletableFuture<Boolean>
+
+	private class OptionTableModel internal constructor(givenOpts: List<IOptionDetails>) : TableModel {
+		private val opts: List<OptionTempHandler>
+
+		init {
+			val mutOpts = ArrayList<OptionTempHandler>()
+			for (opt in givenOpts) {
+				mutOpts.add(OptionTempHandler(opt))
+			}
+			opts = mutOpts
+		}
+
+		override fun getRowCount() = opts.size
+		override fun getColumnCount() = 2
+
+		private val columnNames = arrayOf("Enabled", "Mod name")
+		private val columnTypes = arrayOf(Boolean::class.javaObjectType, String::class.java)
+		private val columnEditables = booleanArrayOf(true, false)
+
+		override fun getColumnName(columnIndex: Int) = columnNames[columnIndex]
+		override fun getColumnClass(columnIndex: Int) = columnTypes[columnIndex]
+		override fun isCellEditable(rowIndex: Int, columnIndex: Int) = columnEditables[columnIndex]
+
+		override fun getValueAt(rowIndex: Int, columnIndex: Int): Any {
+			val opt = opts[rowIndex]
+			return if (columnIndex == 0) opt.optionValue else opt.name
+		}
+
+		override fun setValueAt(aValue: Any, rowIndex: Int, columnIndex: Int) {
+			if (columnIndex == 0) {
+				val opt = opts[rowIndex]
+				opt.optionValue = aValue as Boolean
+			}
+		}
+
+		// Noop, the table model doesn't change!
+		override fun addTableModelListener(l: TableModelListener) {}
+		override fun removeTableModelListener(l: TableModelListener) {}
+
+		fun getDescription(rowIndex: Int) = opts[rowIndex].optionDescription
+
+		fun finalise() {
+			for (opt in opts) {
+				opt.finalise()
+			}
+		}
+	}
+
+	override fun actionPerformed(e: ActionEvent) {
+		if (e.actionCommand == "OK") {
+			tableModel.finalise()
+			future.complete(false)
+			dispose()
+		} else if (e.actionCommand == "Cancel") {
+			future.complete(true)
+			dispose()
+		}
+	}
+
+	/**
+	 * Create the dialog.
+	 */
+	init {
+		tableModel = OptionTableModel(optList)
+		this.future = future
+
+		setBounds(100, 100, 450, 300)
+		setLocationRelativeTo(parentWindow)
+
+		contentPane.apply {
+			layout = BorderLayout()
+			add(JPanel().apply {
+				border = EmptyBorder(5, 5, 5, 5)
+				layout = BorderLayout(0, 0)
+
+				add(JSplitPane().apply {
+					resizeWeight = 0.5
+
+					lblOptionDescription = JTextArea("Select an option...").apply {
+						background = UIManager.getColor("List.background")
+						isOpaque = true
+						wrapStyleWord = true
+						lineWrap = true
+						isEditable = false
+						isFocusable = false
+						font = UIManager.getFont("Label.font")
+						border = EmptyBorder(10, 10, 10, 10)
+					}
+
+					leftComponent = JScrollPane(JTable().apply {
+						showVerticalLines = false
+						showHorizontalLines = false
+						setSelectionMode(ListSelectionModel.SINGLE_SELECTION)
+						setShowGrid(false)
+						model = tableModel
+						columnModel.getColumn(0).resizable = false
+						columnModel.getColumn(0).preferredWidth = 15
+						columnModel.getColumn(0).maxWidth = 15
+						columnModel.getColumn(1).resizable = false
+						selectionModel.addListSelectionListener {
+							val i = selectedRow
+							if (i > -1) {
+								lblOptionDescription.text = tableModel.getDescription(i)
+							} else {
+								lblOptionDescription.text = "Select an option..."
+							}
+						}
+						tableHeader = null
+					}).apply {
+						viewport.background = UIManager.getColor("List.background")
+						horizontalScrollBarPolicy = ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER
+					}
+
+					rightComponent = JScrollPane(lblOptionDescription)
+				})
+
+				add(JPanel().apply {
+					layout = FlowLayout(FlowLayout.RIGHT)
+
+					add(JButton("OK").apply {
+						actionCommand = "OK"
+						addActionListener(this@OptionsSelectWindow)
+
+						this@OptionsSelectWindow.rootPane.defaultButton = this
+					})
+
+					add(JButton("Cancel").apply {
+						actionCommand = "Cancel"
+						addActionListener(this@OptionsSelectWindow)
+					})
+				}, BorderLayout.SOUTH)
+			}, BorderLayout.CENTER)
+		}
+
+		addWindowListener(object : WindowAdapter() {
+			override fun windowClosing(e: WindowEvent) {
+				future.complete(true)
+			}
+
+			override fun windowClosed(e: WindowEvent) {
+				// Just in case closing didn't get triggered - if something else called dispose() the
+				// future will have already completed
+				future.complete(true)
+			}
+		})
+	}
+}

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

@@ -0,0 +1,13 @@
+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)
+	}
+}