Check if file really exists before asking user to overwrite it

app/src/main/java/org/schabi/newpipe/download/DownloadDialog.java

@@ -757,15 +757,14 @@ public class DownloadDialog extends DialogFragment
             return;
         }
 
-        // check if is our file
+        // get state of potential mission referring to the same file
         final MissionState state = downloadManager.checkForExistingMission(storage);
-        @StringRes
-        final int msgBtn;
-        @StringRes
-        final int msgBody;
+        @StringRes final int msgBtn;
+        @StringRes final int msgBody;
 
+        // this switch checks if there is already a mission referring to the same file
         switch (state) {
-            case Finished:
+            case Finished: // there is already a finished mission
                 msgBtn = R.string.overwrite;
                 msgBody = R.string.overwrite_finished_warning;
                 break;
@@ -777,7 +776,7 @@ public class DownloadDialog extends DialogFragment
                 msgBtn = R.string.generate_unique_name;
                 msgBody = R.string.download_already_running;
                 break;
-            case None:
+            case None: // there is no mission referring to the same file
                 if (mainStorage == null) {
                     // This part is called if:
                     // * using SAF on older android version
@@ -812,7 +811,7 @@ public class DownloadDialog extends DialogFragment
                 msgBody = R.string.overwrite_unrelated_warning;
                 break;
             default:
-                return;
+                return; // unreachable
         }
 
         final AlertDialog.Builder askDialog = new AlertDialog.Builder(context)

app/src/main/java/org/schabi/newpipe/streams/io/StoredFileHelper.java

@@ -290,11 +290,10 @@ public class StoredFileHelper implements Serializable {
         }
 
         // WARNING: DocumentFile.exists() and DocumentFile.isFile() methods are slow
-        final boolean exists = docFile == null ? ioFile.exists() : docFile.exists();
-        // ¿docFile.isVirtual() means is no-physical?
-        final boolean isFile = docFile == null ? ioFile.isFile() : docFile.isFile();
-
-        return exists && isFile;
+        // docFile.isVirtual() means it is non-physical?
+        return docFile == null
+                ? (ioFile.exists() && ioFile.isFile())
+                : (docFile.exists() && docFile.isFile());
     }
 
     public boolean create() {

app/src/main/java/us/shandian/giga/service/DownloadManager.java

@@ -106,7 +106,8 @@ public class DownloadManager {
     }
 
     /**
-     * Loads finished missions from the data source
+     * Loads finished missions from the data source and forgets finished missions whose file does
+     * not exist anymore.
      */
     private ArrayList<FinishedMission> loadFinishedMissions() {
         ArrayList<FinishedMission> finishedMissions = mFinishedMissionStore.loadFinishedMissions();
@@ -331,14 +332,29 @@ public class DownloadManager {
     }
 
     /**
-     * Get a finished mission by its path
+     * Get the index into {@link #mMissionsFinished} of a finished mission by its path, return
+     * {@code -1} if there is no such mission. This function also checks if the matched mission's
+     * file exists, and, if it does not, the related mission is forgotten about (like in {@link
+     * #loadFinishedMissions()}) and {@code -1} is returned.
      *
-     * @param storage where the file possible is stored
+     * @param storage where the file would be stored
      * @return the mission index or -1 if no such mission exists
      */
     private int getFinishedMissionIndex(StoredFileHelper storage) {
         for (int i = 0; i < mMissionsFinished.size(); i++) {
             if (mMissionsFinished.get(i).storage.equals(storage)) {
+                // If the file does not exist the mission is not valid anymore. Also checking if
+                // length == 0 since the file picker may create an empty file before yielding it,
+                // but that does not mean the file really belonged to a previous mission.
+                if (!storage.existsAsFile() || storage.length() == 0) {
+                    if (DEBUG) {
+                        Log.d(TAG, "matched downloaded file removed: " + storage.getName());
+                    }
+
+                    mFinishedMissionStore.deleteMission(mMissionsFinished.get(i));
+                    mMissionsFinished.remove(i);
+                    return -1; // finished mission whose associated file was removed
+                }
                 return i;
             }
         }