[duplicated subtitle] Introduce CacheDirUtils for app cache directory selection.

- This commit introduces `CacheDirUtils` to centralize application
  cache directory selection logic.

- The preferred cache directory path is now initialized in 'App.onCreate()'
  and passed to `SubtitleDeduplicator`, instead of relying on 'StateSaver.init().'

Author: TransZAllen

app/src/main/java/org/schabi/newpipe/App.kt

@@ -34,12 +34,14 @@ import org.schabi.newpipe.extractor.services.youtube.extractors.YoutubeStreamExt
 import org.schabi.newpipe.ktx.hasAssignableCause
 import org.schabi.newpipe.settings.NewPipeSettings
 import org.schabi.newpipe.util.BridgeStateSaverInitializer
+import org.schabi.newpipe.util.CacheDirUtils
 import org.schabi.newpipe.util.Localization
 import org.schabi.newpipe.util.ServiceHelper
 import org.schabi.newpipe.util.StateSaver
 import org.schabi.newpipe.util.image.ImageStrategy
 import org.schabi.newpipe.util.image.PreferredImageQuality
 import org.schabi.newpipe.util.potoken.PoTokenProviderImpl
+import org.schabi.newpipe.util.subtitle.SubtitleDeduplicator
 
 /*
  * Copyright (C) Hans-Christoph Steiner 2016 <hans@eds.org>
@@ -93,6 +95,8 @@ open class App :
                 .getInt(getString(R.string.last_used_preferences_version), -1)
         isFirstRun = lastUsedPrefVersion == -1
 
+        val appCacheDirPath = CacheDirUtils.getPreferredAppCacheDirPath(this)
+
         // Initialize settings first because other initializations can use its values
         NewPipeSettings.initSettings(this)
 
@@ -124,6 +128,8 @@ open class App :
         configureRxJavaErrorHandler()
 
         YoutubeStreamExtractor.setPoTokenProvider(PoTokenProviderImpl)
+
+        SubtitleDeduplicator.setCacheDirPath(appCacheDirPath)
     }
 
     override fun newImageLoader(context: Context): ImageLoader = ImageLoader

app/src/main/java/org/schabi/newpipe/util/CacheDirUtils.java

@@ -0,0 +1,66 @@
+package org.schabi.newpipe.util;
+
+import java.io.File;
+
+import android.content.Context;
+import androidx.annotation.NonNull;
+
+public final class CacheDirUtils {
+
+    private CacheDirUtils() {
+        // no instance
+    }
+
+    public static String getExternalAppCacheDirPath(
+                                @NonNull final Context context) {
+        final File externalCacheDir = context.getExternalCacheDir();
+        if (null != externalCacheDir) {
+            // /storage/emulated/0/Android/data/<package_name>/cache/
+            return externalCacheDir.getAbsolutePath();
+        }
+
+        return null;
+    }
+
+    public static String getInternalAppCacheDirPath(
+                                @NonNull final Context context) {
+        // always available, never be 'null'
+        // /data/user/0/<package_name>/cache/
+        return context.getCacheDir().getAbsolutePath();
+    }
+
+    /**
+     * Returns the preferred cache directory path for the application.
+     *
+     * Prefers the external cache directory when available
+     * (user-accessible, larger space),
+     * falls back to the internal private cache directory otherwise
+     * (always available, more secure).
+     *
+     * Typical paths:
+     * - External: /storage/emulated/0/Android/data/<package_name>/cache/
+     * - Internal: /data/user/0/<package_name>/cache/
+     *             (or /data/data/<package_name>/cache/ on some devices)
+     *
+     * Note: The 'external' and 'internal' cache directories mentioned above
+     * are Android terms. They are typically located on the device's
+     * built-in storage and are not related to removable SD/TF cards.
+     *
+     * User "Clear Cache" in app settings deletes files in both locations.
+     *
+     * @param context used to get the available cache dir
+     * @return absolute path string, never null
+     */
+    @NonNull
+    public static String getPreferredAppCacheDirPath(
+                                @NonNull final Context context) {
+
+        final String externalCacheDirPath = getExternalAppCacheDirPath(context);
+        if (null != externalCacheDirPath) {
+            return externalCacheDirPath;
+        }
+
+        // Internal cache dir should always be available
+        return getInternalAppCacheDirPath(context);
+    }
+}