change the ReviewHelper for api called

app/src/main/java/fr/free/nrw/commons/review/ReviewActivity.java

@@ -12,6 +12,7 @@ import android.view.MenuInflater;
 import android.view.MenuItem;
 import android.view.MotionEvent;
 import android.view.View;
+import androidx.core.util.Pair;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentManager;
 import fr.free.nrw.commons.Media;
@@ -62,9 +63,14 @@ public class ReviewActivity extends BaseActivity {
 
     private List<Media> cachedMedia = new ArrayList<>();
 
+    /** Constants for managing media cache in the review activity */
+    // Name of SharedPreferences file for storing review activity preferences
     private static final String PREF_NAME = "ReviewActivityPrefs";
+    // Key for storing the timestamp of last cache update
     private static final String LAST_CACHE_TIME_KEY = "lastCacheTime";
+    // Maximum number of media files to store in cache
     private static final int CACHE_SIZE = 50;
+    // Cache expiration time in milliseconds (24 hours)
     private static final long CACHE_EXPIRY_TIME = 24 * 60 * 60 * 1000;
 
     @Override
@@ -113,10 +119,21 @@ public class ReviewActivity extends BaseActivity {
         Drawable d[]=binding.skipImage.getCompoundDrawablesRelative();
         d[2].setColorFilter(getApplicationContext().getResources().getColor(R.color.button_blue), PorterDuff.Mode.SRC_IN);
 
+        /**
+         * Restores the previous state of the activity or initializes a new review session.
+         * Checks if there's a saved media state from a previous session (e.g., before screen rotation).
+         * If found, restores the last viewed image and its detail view.
+         * Otherwise, starts a new random image review session.
+         *
+         * @param savedInstanceState Bundle containing the activity's previously saved state, if any
+         */
         if (savedInstanceState != null && savedInstanceState.getParcelable(SAVED_MEDIA) != null) {
+            // Restore the previously viewed image if state exists
             updateImage(savedInstanceState.getParcelable(SAVED_MEDIA));
+            // Restore media detail view (handles configuration changes like screen rotation)
             setUpMediaDetailOnOrientation();
         } else {
+            // Start fresh review session with a random image
             runRandomizer();
         }
 
@@ -145,54 +162,173 @@ public class ReviewActivity extends BaseActivity {
         return true;
     }
 
+    /**
+     * Initiates the process of loading a random media file for review.
+     * This method:
+     * - Resets the UI state
+     * - Shows loading indicator
+     * - Manages media cache
+     * - Either loads from cache or fetches new media
+     *
+     * The method is annotated with @SuppressLint("CheckResult") as the Observable
+     * subscription is handled through CompositeDisposable in the implementation.
+     *
+     * @return true indicating successful initiation of the randomization process
+     */
     @SuppressLint("CheckResult")
     public boolean runRandomizer() {
+        // Reset flag for tracking presence of non-hidden categories
         hasNonHiddenCategories = false;
+        // Display loading indicator while fetching media
         binding.pbReviewImage.setVisibility(View.VISIBLE);
+        // Reset view pager to first page
         binding.viewPagerReview.setCurrentItem(0);
 
+        // Check cache status and determine source of next media
         if (cachedMedia.isEmpty() || isCacheExpired()) {
+            // Fetch and cache new media if cache is empty or expired
             fetchAndCacheMedia();
         } else {
+            // Use next media file from existing cache
             processNextCachedMedia();
         }
         return true;
     }
 
-    private void fetchAndCacheMedia() {
-        compositeDisposable.add(Observable.range(0, CACHE_SIZE)
-            .flatMap(i -> reviewHelper.getRandomMedia().toObservable())
-            .subscribeOn(Schedulers.io())
-            .observeOn(AndroidSchedulers.mainThread())
-            .toList()
-            .subscribe(mediaList -> {
-                cachedMedia.clear();
-                cachedMedia.addAll(mediaList);
-                updateLastCacheTime();
-                processNextCachedMedia();
-            }, this::handleError));
+    /**
+     * Batch checks whether multiple files from the cache are used in wikis.
+     * This is a more efficient way to process multiple files compared to checking them one by one.
+     *
+     * @param mediaList List of Media objects to check for usage
+     */
+    /**
+     * Batch checks whether multiple files from the cache are used in wikis.
+     * This is a more efficient way to process multiple files compared to checking them one by one.
+     *
+     * @param mediaList List of Media objects to check for usage
+     */
+    private void batchCheckFilesUsage(List<Media> mediaList) {
+        // Extract filenames from media objects
+        List<String> filenames = new ArrayList<>();
+        for (Media media : mediaList) {
+            if (media.getFilename() != null) {
+                filenames.add(media.getFilename());
+            }
+        }
+
+        compositeDisposable.add(
+            reviewHelper.checkFileUsageBatch(filenames)
+                .subscribeOn(Schedulers.io())
+                .observeOn(AndroidSchedulers.mainThread())
+                .toList()
+                .subscribe(results -> {
+                    // Process each result
+                    for (kotlin.Pair<String, Boolean> result : results) {
+                        String filename = result.getFirst();
+                        Boolean isUsed = result.getSecond();
+
+                        // Find corresponding media object
+                        for (Media media : mediaList) {
+                            if (filename.equals(media.getFilename())) {
+                                if (!isUsed) {
+                                    // If file is not used, proceed with category check
+                                    findNonHiddenCategories(media);
+                                }
+                                break;
+                            }
+                        }
+                    }
+                }, this::handleError));
     }
 
+
+    /**
+     * Fetches and caches new media files for review.
+     * Uses RxJava to:
+     * - Generate a range of indices for the desired cache size
+     * - Fetch random media files asynchronously
+     * - Handle thread scheduling between IO and UI operations
+     * - Store the fetched media in cache
+     *
+     * The operation is added to compositeDisposable for proper lifecycle management.
+     */
+    private void fetchAndCacheMedia() {
+        compositeDisposable.add(
+            Observable.range(0, CACHE_SIZE)
+                .flatMap(i -> reviewHelper.getRandomMedia().toObservable())
+                .subscribeOn(Schedulers.io())
+                .observeOn(AndroidSchedulers.mainThread())
+                .toList()
+                .subscribe(mediaList -> {
+                    // Clear existing cache
+                    cachedMedia.clear();
+
+                    // Start batch check process
+                    batchCheckFilesUsage(mediaList);
+
+                    // Update cache with new media
+                    cachedMedia.addAll(mediaList);
+                    updateLastCacheTime();
+
+                    // Process first media item if available
+                    if (!cachedMedia.isEmpty()) {
+                        processNextCachedMedia();
+                    }
+                }, this::handleError));
+    }
+
+    /**
+     * Processes the next media file from the cache.
+     * If cache is not empty, removes and processes the first media file.
+     * If cache is empty, triggers a new fetch operation.
+     *
+     * This method ensures continuous flow of media files for review
+     * while maintaining the cache mechanism.
+     */
     private void processNextCachedMedia() {
         if (!cachedMedia.isEmpty()) {
+            // Remove and get the first media from cache
             Media media = cachedMedia.remove(0);
+
             checkWhetherFileIsUsedInWikis(media);
         } else {
+            // Refill cache if empty
             fetchAndCacheMedia();
         }
     }
 
+    /**
+     * Checks if the current cache has expired.
+     * Cache expiration is determined by comparing the last cache time
+     * with the current time against the configured expiry duration.
+     *
+     * @return true if cache has expired, false otherwise
+     */
     private boolean isCacheExpired() {
+        // Get shared preferences instance
         SharedPreferences prefs = getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
+
         long lastCacheTime = prefs.getLong(LAST_CACHE_TIME_KEY, 0);
+
         long currentTime = System.currentTimeMillis();
+
         return (currentTime - lastCacheTime) > CACHE_EXPIRY_TIME;
     }
 
+
+    /**
+     * Updates the timestamp of the last cache operation.
+     * Stores the current time in SharedPreferences to track
+     * cache freshness for future operations.
+     */
     private void updateLastCacheTime() {
+
         SharedPreferences prefs = getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
+
         SharedPreferences.Editor editor = prefs.edit();
+        // Store current timestamp as last cache time
         editor.putLong(LAST_CACHE_TIME_KEY, System.currentTimeMillis());
+        // Apply changes asynchronously
         editor.apply();
     }
 
@@ -305,10 +441,20 @@ public class ReviewActivity extends BaseActivity {
                 null,
                 null);
     }
+    /**
+     * Handles errors that occur during media processing operations.
+     * This is a generic error handler that:
+     * - Hides the loading indicator
+     * - Shows a user-friendly error message via Snackbar
+     *
+     * Used as error callback for RxJava operations and other async tasks.
+     *
+     * @param error The Throwable that was caught during operation
+     */
     private void handleError(Throwable error) {
         binding.pbReviewImage.setVisibility(View.GONE);
+        // Show error message to user via Snackbar
         ViewUtil.showShortSnackbar(binding.drawerLayout, R.string.error_review);
-
     }
 
 

app/src/main/java/fr/free/nrw/commons/review/ReviewHelper.kt

@@ -26,13 +26,11 @@ class ReviewHelper
 
 
     /**
-     * Gets multiple random media items for review.
-     * - Fetches recent changes and filters them
-     * - Checks if files are nominated for deletion
-     * - Filters out already reviewed images
+     * Fetches recent changes from MediaWiki API
+     * Calls the API to get the latest 50 changes
+     * When more results are available, the query gets continued beyond this range
      *
-     * @param count Number of media items to fetch
-     * @return Observable of Media items
+     * @return
      */
         private fun getRecentChanges() =
             reviewInterface
@@ -136,13 +134,29 @@ class ReviewHelper
 
 
 
+
+    /**
+     * Batch checks whether multiple files are being used in any wiki pages.
+     * This method processes a list of filenames in parallel using RxJava Observables.
+     *
+     * @param filenames A list of filenames to check for usage
+     * @return Observable emitting pairs of filename and usage status:
+     *         - The String represents the filename
+     *         - The Boolean indicates whether the file is used (true) or not (false)
+     *         If an error occurs during processing, it will log the error and emit an empty Observable
+     */
     fun checkFileUsageBatch(filenames: List<String>): Observable<Pair<String, Boolean>> =
+        // Convert the list of filenames into an Observable stream
         Observable.fromIterable(filenames)
+            // For each filename, check its usage and pair it with the result
             .flatMap { filename ->
                 checkFileUsage(filename)
+                    // Create a pair of the filename and its usage status
                     .map { isUsed -> Pair(filename, isUsed) }
             }
+            // Handle any errors that occur during processing
             .onErrorResumeNext { error: Throwable ->
+                // Log the error and continue with an empty Observable
                 Timber.e(error, "Error checking file usage batch")
                 Observable.empty()
             }