RegEditLinux: Find VRChat install location for registry parsing

Fixes VRChat config warnings not working when VRChat is installed at
a library location other than the default.

Author: ImSapphire

server/desktop/src/main/java/dev/slimevr/desktop/games/vrchat/RegEdit.kt

@@ -12,6 +12,7 @@ import java.io.FileReader
 import java.io.InvalidObjectException
 import java.nio.ByteBuffer
 import java.nio.ByteOrder
+import java.nio.file.Path
 import kotlin.io.path.Path
 import kotlin.io.path.exists
 
@@ -142,13 +143,78 @@ class RegEditLinux : AbstractRegEdit() {
 	}
 
 	companion object {
-		const val USER_REG_SUBPATH = "steamapps/compatdata/438100/pfx/user.reg"
-		val USER_REG_PATH =
-			System.getenv("HOME")?.let {
-				Path(it, ".steam", "root", USER_REG_SUBPATH).let { if (it.exists()) it else null }
-					?: Path(it, ".steam", "debian-installation", USER_REG_SUBPATH).let { if (it.exists()) it else null }
-					?: Path(it, ".var", "app", "com.valvesoftware.Steam", "data", "Steam", USER_REG_SUBPATH).let { if (it.exists()) it else null }
+		private fun findAppLibraryLocation(steamPath: Path, appId: Int): Path? {
+			val keyValueRegex = Regex(""""(\w+)"[ \t]*(?:"(.+)")?""")
+			try {
+				BufferedReader(FileReader(steamPath.resolve("config/libraryfolders.vdf").toFile())).use { reader ->
+					var depth = 0
+					var currentLibraryPath: Path? = null
+
+					while (reader.ready()) {
+						val line = reader.readLine().trim()
+						if (line == "{") {
+							depth += 1
+							continue
+						}
+						if (line == "}") {
+							depth -= 1
+							continue
+						}
+
+						keyValueRegex.matchEntire(line)?.let {
+							val key = it.groupValues[1]
+							val value = it.groupValues[2]
+
+							when (depth) {
+								0 -> {
+									require(key == "libraryfolders") { "root key must be libraryfolders" }
+								}
+
+								1 -> {
+									// start of a library node
+								}
+
+								2 -> {
+									// in a library node
+									if (key == "path") {
+										currentLibraryPath = Path(value)
+									} else if (key == "apps") {
+										// start of apps node
+										require(currentLibraryPath != null) { "path must come before apps in node" }
+									}
+								}
+
+								3 -> {
+									// in apps node
+									val curAppId = try {
+										key.toInt()
+									} catch (_: NumberFormatException) {
+										null
+									}
+									if (curAppId != null && curAppId == appId) {
+										assert(currentLibraryPath != null)
+										return currentLibraryPath
+									}
+								}
+							}
+						}
+					}
+					LogManager.warning("[VRChatRegEdit] Couldn't find library folder for appid $appId")
+				}
+			} catch (e: Exception) {
+				LogManager.severe("[VRChatRegEdit] Error parsing Steam libraryfolders", e)
 			}
+			return null
+		}
+
+		const val USER_REG_SUBPATH = "steamapps/compatdata/438100/pfx/user.reg"
+		val STEAM_PATH = System.getenv("HOME")?.let { home ->
+			Path(home, ".steam", "root").takeIf { it.exists() }
+				?: Path(home, ".steam", "debian-installation").takeIf { it.exists() }
+				?: Path(home, ".var", "app", "com.valvesoftware.Steam", "data", "Steam").takeIf { it.exists() }
+		}
+		val USER_REG_PATH: Path? = if (STEAM_PATH != null) findAppLibraryLocation(STEAM_PATH, 438100)?.resolve(USER_REG_SUBPATH) else null
+
 		val KEY_VALUE_PATTERN = Regex(""""(.+)"=(.+)""")
 
 		val HEX_FORMAT = HexFormat {