change to tasks and base deletion on file index instead of name.

Author: annzimmer

firebase-ml-modeldownloader/src/main/java/com/google/firebase/ml/modeldownloader/internal/ModelFileDownloadService.java

@@ -409,11 +409,7 @@ public File loadNewlyDownloadedModelFile(CustomModel model) {
           new CustomModel(
               model.getName(), model.getModelHash(), model.getSize(), 0, newModelFile.getPath()));
 
-      try {
-        maybeCleanUpOldModels();
-      } catch (FirebaseMlException fex) {
-        Log.d(TAG, "Failed to clean up old models.");
-      }
+      maybeCleanUpOldModels();
 
       return newModelFile;
     } else if (statusCode == DownloadManager.STATUS_FAILED) {
@@ -428,17 +424,22 @@ public File loadNewlyDownloadedModelFile(CustomModel model) {
     return null;
   }
 
-  private void maybeCleanUpOldModels() throws FirebaseMlException {
+  private Task<Void> maybeCleanUpOldModels() {
     if (!isInitialLoad) {
-      return;
+      return Tasks.forResult(null);
     }
 
-    // only do once per initialization
+    // only do once per initialization.
     isInitialLoad = false;
 
     // for each custom model directory, find out the latest model and delete the other files.
-    // If no corresponding model, clean up the full direcorty.
-    fileManager.deleteNonLatestCustomModels();
+    // If no corresponding model, clean up the full directory.
+    try {
+      fileManager.deleteNonLatestCustomModels();
+    } catch (FirebaseMlException fex) {
+      Log.d(TAG, "Failed to clean up old models.");
+    }
+    return Tasks.forResult(null);
   }
 
   private FirebaseMlException getExceptionAccordingToDownloadManager(Long downloadId) {

firebase-ml-modeldownloader/src/main/java/com/google/firebase/ml/modeldownloader/internal/ModelFileManager.java

@@ -204,23 +204,30 @@ public synchronized File moveModelToDestinationFolder(
    * @param latestModelFilePath The file path to the latest custom model.
    */
   @WorkerThread
-  public synchronized boolean deleteOldModels(
+  public synchronized void deleteOldModels(
       @NonNull String modelName, @NonNull String latestModelFilePath) {
     File modelFolder = getModelDirUnsafe(modelName);
     if (!modelFolder.exists()) {
-      return false;
+      return;
     }
 
+    File latestFile = new File(latestModelFilePath);
+    int latestIndex = Integer.parseInt(latestFile.getName());
     File[] modelFiles = modelFolder.listFiles();
 
     boolean isAllDeleted = true;
+    int fileInt;
     for (File modelFile : modelFiles) {
-      if (!modelFile.getPath().equals(latestModelFilePath) && !deleteRecursively(modelFile)) {
-        isAllDeleted = false;
+      try {
+        fileInt = Integer.parseInt(modelFile.getName());
+      } catch (NumberFormatException ex) {
+        // unexpected file - ignore
+        fileInt = Integer.MAX_VALUE;
+      }
+      if (fileInt < latestIndex) {
+        isAllDeleted = isAllDeleted && modelFile.delete();
       }
     }
-    // Only return true if all old models are deleted.
-    return isAllDeleted;
   }
 
   /**

firebase-ml-modeldownloader/src/test/java/com/google/firebase/ml/modeldownloader/internal/ModelFileManagerTest.java

@@ -238,6 +238,18 @@ public void deleteOldModels_deleteModel() throws FirebaseMlException, FileNotFou
     assertTrue(new File(modelDestinationFolder + "/1").exists());
   }
 
+  @Test
+  public void deleteOldModels_deleteModel_keepNewer()
+      throws FirebaseMlException, FileNotFoundException {
+    MoveFileToDestination(modelDestinationFolder, testModelFile, CUSTOM_MODEL_NO_FILE, 0);
+    MoveFileToDestination(modelDestinationFolder, testModelFile2, CUSTOM_MODEL_NO_FILE, 1);
+
+    fileManager.deleteOldModels(MODEL_NAME, modelDestinationFolder + "/0");
+
+    assertTrue(new File(modelDestinationFolder + "/0").exists());
+    assertTrue(new File(modelDestinationFolder + "/1").exists());
+  }
+
   @Test
   public void deleteOldModels_noModelsToDelete() throws FirebaseMlException, FileNotFoundException {
     MoveFileToDestination(modelDestinationFolder, testModelFile, CUSTOM_MODEL_NO_FILE, 0);