[duplicated subtitle] Support downloading local subtitles after deduplication (SubtitleDeduplicator)

- Introduce `SubtitleDeduplicator` into NewPipeExtractor; subtitles are now cached locally.
- Add support for `file://` protocol to process local subtitle files (e.g., file:///storage/emulated/0/Android/data/<package_name>/cache/subtitle_cache/<cached_TTML_subtitle_name>) instead of remote URLs.
- Separate handling of local and remote subtitle in `run()` for better clarity.
  Note: After calling `SubtitleDeduplicator.checkAndDeduplicate()`, all YouTube subtitles are local.
- Clarify the early return logic for single-URL subtitle download.

Author: TransZAllen

app/src/main/java/us/shandian/giga/get/DownloadInitializer.java

@@ -11,11 +11,15 @@
 import java.io.InterruptedIOException;
 import java.net.HttpURLConnection;
 import java.nio.channels.ClosedByInterruptException;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
 
 import us.shandian.giga.util.Utility;
 
 import static org.schabi.newpipe.BuildConfig.DEBUG;
 import static us.shandian.giga.get.DownloadMission.ERROR_HTTP_FORBIDDEN;
+import org.schabi.newpipe.extractor.utils.SubtitleDeduplicator;
 
 public class DownloadInitializer extends Thread {
     private static final String TAG = "DownloadInitializer";
@@ -46,6 +50,23 @@ public void run() {
         int retryCount = 0;
         int httpCode = 204;
 
+        //process local file URI (file://)
+        for (int i = 0; i < mMission.urls.length && mMission.running; i++) {
+            String currentUrl = mMission.urls[i];
+
+            if (true == islocalSubtitleUri(currentUrl)) {
+                LocalSubtitleConverter.convertLocalTtmlToVtt(currentUrl, mMission);
+
+                // Subtitle download missions always contain exactly one URL.
+                // Once the local subtitle is converted, the mission is
+                // considered finished.
+                // Do not replace this with `continue` unless subtitle missions
+                // support multiple URLs in the future.
+                return;
+            }
+        }
+
+        // process remote, for example: http:// or https://
         while (true) {
             try {
                 if (mMission.blocks == null && mMission.current == 0) {
@@ -54,6 +75,7 @@ public void run() {
                     long lowestSize = Long.MAX_VALUE;
 
                     for (int i = 0; i < mMission.urls.length && mMission.running; i++) {
+
                         mConn = mMission.openConnection(mMission.urls[i], true, 0, 0);
                         mMission.establishConnection(mId, mConn);
                         dispose();
@@ -205,4 +227,34 @@ public void interrupt() {
         super.interrupt();
         if (mConn != null) dispose();
     }
+
+    private boolean isLocalUri(String url) {
+        String URL_PREFIX = SubtitleDeduplicator.LOCAL_SUBTITLE_URL_PREFIX;
+
+        if (url.startsWith(URL_PREFIX)) {
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    private boolean isSubtitleDownloadMission() {
+        char downloadKind = mMission.kind;
+        if ('s' == downloadKind) {
+            return true;
+        }
+
+        return false;
+    }
+
+    private boolean islocalSubtitleUri(String url) {
+        if (true == isSubtitleDownloadMission()) {
+            if (true == isLocalUri(url)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
 }

app/src/main/java/us/shandian/giga/get/LocalSubtitleConverter.java

@@ -0,0 +1,115 @@
+package us.shandian.giga.get;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InterruptedIOException;
+import android.util.Log;
+
+import org.schabi.newpipe.streams.io.SharpStream;
+
+import org.schabi.newpipe.extractor.utils.SubtitleDeduplicator;
+
+final class LocalSubtitleConverter {
+
+    private static final String TAG = "LocalSubtitleConverter";
+
+    private LocalSubtitleConverter() {
+        // no instance
+    }
+
+    /**
+     * Converts a local(file://) TTML subtitle file into VTT format
+     * and stores it in the user-defined/chosen directory.
+     *
+     * @param localSubtitleUri file:// URI of the local TTML subtitle
+     * @param subtitleMission current download mission, and it is a command
+     *                initiated manually by the user (via a button).
+     * @return 0 if success, non-zero error code otherwise
+     */
+    public static int convertLocalTtmlToVtt(String localSubtitleUri,
+                                       DownloadMission subtitleMission) {
+
+        if (!isValidLocalUri(localSubtitleUri)) {
+            return 1;
+        }
+
+        File ttmlFile = new File(
+                getAbsolutePathFromLocalUri(localSubtitleUri)
+        );
+
+        if (!ttmlFile.exists()) {
+            subtitleMission.notifyError(DownloadMission.ERROR_FILE_CREATION, null);
+            return 2;
+        }
+
+        if (!subtitleMission.storage.canWrite()) {
+            subtitleMission.notifyError(DownloadMission.ERROR_PERMISSION_DENIED, null);
+            return 3;
+        }
+
+        writeLocalTtmlAsVtt(ttmlFile, subtitleMission);
+
+        printLocalSubtitleConvertedOk(subtitleMission);
+
+        return 0;
+    }
+
+
+    private static boolean isValidLocalUri(String localUri) {
+        String URL_PREFIX = SubtitleDeduplicator.LOCAL_SUBTITLE_URL_PREFIX;
+
+        if (localUri.length() <= URL_PREFIX.length()) {
+             return false;
+        }
+
+        return true;
+    }
+
+    private static String getAbsolutePathFromLocalUri(String localSubtitleUri) {
+        String URL_PREFIX = SubtitleDeduplicator.LOCAL_SUBTITLE_URL_PREFIX;
+        int prefixLength = URL_PREFIX.length();
+        // Remove URL_PREFIX
+        String absolutePath = localSubtitleUri.substring(prefixLength);
+        return absolutePath;
+    }
+
+    private static void writeLocalTtmlAsVtt(File localTtmlFile,
+                                            DownloadMission mission) {
+        try (FileInputStream inputTtmlStream = new FileInputStream(localTtmlFile);
+             SharpStream outputVttStream = mission.storage.getStream()) {
+
+            byte[] buffer = new byte[DownloadMission.BUFFER_SIZE];
+            int bytesRead;
+            long totalBytes = 0;
+
+            while ((bytesRead = inputTtmlStream.read(buffer)) != -1) {
+                outputVttStream.write(buffer, 0, bytesRead);
+                totalBytes += bytesRead;
+                mission.notifyProgress(bytesRead);
+            }
+
+            mission.length = totalBytes;
+            mission.unknownLength = false;
+            mission.notifyFinished();
+
+        } catch (IOException e) {
+            String logMessage = "Error extracting subtitle paragraphs from " +
+                                localTtmlFile.getAbsolutePath() + ", error:" +
+                                e.getMessage();
+            Log.e(TAG, logMessage);
+            mission.notifyError(DownloadMission.ERROR_FILE_CREATION, e);
+        }
+    }
+
+    private static void printLocalSubtitleConvertedOk(DownloadMission mission) {
+        try {
+            String logMessage = "Local subtitle uri is extracted to:" +
+                                mission.storage.getName();
+            Log.i(TAG, logMessage);
+        } catch (NullPointerException e) {
+            Log.w(TAG, "Fail to convert ttml subtitle to vtt.", e);
+        }
+    }
+}