Fix Swing multithreading issue, clean up slightly

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

@@ -18,6 +18,9 @@ import kotlin.system.exitProcess
 
 @Suppress("unused")
 class Main(args: Array<String>) {
+	// Don't attempt to start a GUI if we are headless
+	var guiEnabled = !GraphicsEnvironment.isHeadless()
+
 	private fun startup(args: Array<String>) {
 		val options = Options()
 		addNonBootstrapOptions(options)
@@ -28,19 +31,24 @@ class Main(args: Array<String>) {
 			parser.parse(options, args)
 		} catch (e: ParseException) {
 			e.printStackTrace()
+			if (guiEnabled) {
+				EventQueue.invokeAndWait {
 					try {
 						UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName())
-			} catch (e1: Exception) {
+					} catch (ignored: 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()
+		if (guiEnabled && cmd.hasOption("no-gui")) {
+			guiEnabled = false
+		}
+
+		val ui = if (guiEnabled) InstallWindow() else CLIHandler()
 
 		val unparsedArgs = cmd.args
 		if (unparsedArgs.size > 1) {
@@ -49,15 +57,13 @@ class Main(args: Array<String>) {
 			ui.handleExceptionAndExit(RuntimeException("URI to install from must be specified!"))
 		}
 
-		cmd.getOptionValue("title")?.also {
-			ui.setTitle(it)
-		}
+		cmd.getOptionValue("title")?.also(ui::setTitle)
 
 		val inputStateHandler = InputStateHandler()
 		ui.show(inputStateHandler)
 
 		val uOptions = UpdateManager.Options().apply {
-			side = cmd.getOptionValue("side")?.let { UpdateManager.Options.Side.from(it) } ?: side
+			side = cmd.getOptionValue("side")?.let((UpdateManager.Options.Side)::from) ?: side
 			packFolder = cmd.getOptionValue("pack-folder") ?: packFolder
 			manifestFile = cmd.getOptionValue("meta-file") ?: manifestFile
 		}
@@ -113,12 +119,14 @@ class Main(args: Array<String>) {
 			startup(args)
 		} catch (e: Exception) {
 			e.printStackTrace()
+			if (guiEnabled) {
 				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/ui/InstallWindow.kt

@@ -10,10 +10,10 @@ 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 lateinit var frmPackwizlauncher: JFrame
+	private lateinit var lblProgresslabel: JLabel
+	private lateinit var progressBar: JProgressBar
+	private lateinit var btnOptions: JButton
 
 	private var inputStateHandler: InputStateHandler? = null
 	private var title = "Updating modpack..."
@@ -23,6 +23,7 @@ class InstallWindow : IUserInterface {
 	// TODO: separate JFrame junk from IUserInterface junk?
 
 	init {
+		EventQueue.invokeAndWait {
 			frmPackwizlauncher = JFrame().apply {
 				title = this@InstallWindow.title
 				setBounds(100, 100, 493, 95)
@@ -74,6 +75,7 @@ class InstallWindow : IUserInterface {
 				}, BorderLayout.EAST)
 			}
 		}
+	}
 
 	override fun show(handler: InputStateHandler) {
 		inputStateHandler = handler