Fix: Adding custom games from USB OTG drives silently fails

app/src/main/java/app/gamenative/ui/components/CustomGameFolderPicker.kt

@@ -16,10 +16,50 @@ import app.gamenative.R
 import app.gamenative.utils.CustomGameScanner
 
 /**
- * Converts a document tree URI to a file path.
- * Returns null if conversion fails.
+ * Resolves the filesystem root of a storage volume identified by the volume id
+ * from a document tree URI (e.g. "6A1F-93F0").
+ *
+ * SD cards typically live at /storage/<uuid>, but USB OTG drives on some devices
+ * (e.g. Samsung) are only mounted at the path reported by
+ * [android.os.storage.StorageVolume.getDirectory] (such as /mnt/media_rw/<uuid>),
+ * with no /storage view at all.
+ *
+ * @param context Used to query [android.os.storage.StorageManager] for mounted volumes.
+ * @param volumeId The volume id portion of a tree document id (the part before ":").
+ * @return The volume's mount point. Prefers /storage/<volumeId> when it exists,
+ *         otherwise the directory reported by StorageManager, falling back to
+ *         /storage/<volumeId> when the volume cannot be resolved.
  */
-fun getPathFromTreeUri(uri: Uri?): String? {
+private fun resolveVolumeRoot(context: Context, volumeId: String): String {
+    val defaultRoot = "/storage/$volumeId"
+    if (java.io.File(defaultRoot).exists()) {
+        return defaultRoot
+    }
+    val sm = context.getSystemService(android.os.storage.StorageManager::class.java)
+    val volume = sm?.storageVolumes?.firstOrNull {
+        it.uuid?.equals(volumeId, ignoreCase = true) == true
+    }
+    val resolved = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+        volume?.directory?.absolutePath
+    } else {
+        null
+    }
+    return resolved ?: defaultRoot
+}
+
+/**
+ * Converts a document tree URI (from e.g. [ActivityResultContracts.OpenDocumentTree])
+ * to a raw filesystem path.
+ *
+ * Handles the primary volume ("primary:" document ids) as well as secondary volumes
+ * such as SD cards and USB OTG drives, whose mount point is resolved via
+ * [resolveVolumeRoot].
+ *
+ * @param context Used to resolve secondary volume mount points.
+ * @param uri The tree URI returned by the document picker, or null.
+ * @return The resolved filesystem path, or null if [uri] is null or conversion fails.
+ */
+fun getPathFromTreeUri(context: Context, uri: Uri?): String? {
     if (uri == null) return null
 
     return try {
@@ -41,16 +81,12 @@ fun getPathFromTreeUri(uri: Uri?): String? {
                 if (parts.size == 2) {
                     val volumeId = parts[0]
                     val path = parts[1]
-                    val possiblePath = if (path.isEmpty()) {
-                        "/storage/$volumeId"
+                    val volumeRoot = resolveVolumeRoot(context, volumeId)
+                    return if (path.isEmpty()) {
+                        volumeRoot
                     } else {
-                        "/storage/$volumeId/$path"
-                    }
-                    val file = java.io.File(possiblePath)
-                    if (file.exists() || file.parentFile?.exists() == true) {
-                        return possiblePath
+                        "$volumeRoot/$path"
                     }
-                    return possiblePath
                 }
             }
 
@@ -127,7 +163,7 @@ fun rememberCustomGameFolderPicker(
             return@rememberLauncherForActivityResult
         }
 
-        val path = getPathFromTreeUri(uri)
+        val path = getPathFromTreeUri(context, uri)
         if (path != null) {
             onPathSelected(path)
         } else {