Fixes #5743 Reduce delay between peer reviews

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

@@ -3,6 +3,7 @@
 import android.annotation.SuppressLint;
 import android.content.Context;
 import android.content.Intent;
+import android.content.SharedPreferences;
 import android.graphics.PorterDuff;
 import android.graphics.drawable.Drawable;
 import android.os.Bundle;
@@ -11,6 +12,7 @@
 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;
@@ -22,19 +24,25 @@
 import fr.free.nrw.commons.theme.BaseActivity;
 import fr.free.nrw.commons.utils.DialogUtil;
 import fr.free.nrw.commons.utils.ViewUtil;
+import io.reactivex.Observable;
 import io.reactivex.android.schedulers.AndroidSchedulers;
 import io.reactivex.disposables.CompositeDisposable;
 import io.reactivex.schedulers.Schedulers;
+import java.util.ArrayList;
+import java.util.List;
 import javax.inject.Inject;
 
 public class ReviewActivity extends BaseActivity {
 
-
     private ActivityReviewBinding binding;
 
     MediaDetailFragment mediaDetailFragment;
     public ReviewPagerAdapter reviewPagerAdapter;
     public ReviewController reviewController;
+
+
+
+
     @Inject
     ReviewHelper reviewHelper;
     @Inject
@@ -53,6 +61,20 @@ public class ReviewActivity extends BaseActivity {
     final String SAVED_MEDIA = "saved_media";
     private Media media;
 
+    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 = 5;
+    // Cache expiration time in milliseconds (24 hours)
+
+    private static final long CACHE_EXPIRY_TIME = 24 * 60 * 60 * 1000;
+
     @Override
     protected void onSaveInstanceState(Bundle outState) {
         super.onSaveInstanceState(outState);
@@ -99,11 +121,22 @@ protected void onCreate(Bundle savedInstanceState) {
         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) {
-            updateImage(savedInstanceState.getParcelable(SAVED_MEDIA)); // Use existing media if we have one
+            // 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 {
-            runRandomizer(); //Run randomizer whenever everything is ready so that a first random image will be added
+            // Start fresh review session with a random image
+            runRandomizer();
         }
 
         binding.skipImage.setOnClickListener(view -> {
@@ -131,36 +164,190 @@ public boolean onSupportNavigateUp() {
         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);
-        // Finds non-hidden categories from Media instance
-        compositeDisposable.add(reviewHelper.getRandomMedia()
+
+        // 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;
+    }
+
+    /**
+     * 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())
-                .subscribe(this::checkWhetherFileIsUsedInWikis));
-        return true;
+                .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();
     }
 
     /**
      * Check whether media is used or not in any Wiki Page
      */
-    @SuppressLint("CheckResult")
     private void checkWhetherFileIsUsedInWikis(final Media media) {
         compositeDisposable.add(reviewHelper.checkFileUsage(media.getFilename())
             .subscribeOn(Schedulers.io())
             .observeOn(AndroidSchedulers.mainThread())
             .subscribe(result -> {
-                // result false indicates media is not used in any wiki
                 if (!result) {
-                    // Finds non-hidden categories from Media instance
                     findNonHiddenCategories(media);
                 } else {
-                    runRandomizer();
+                    processNextCachedMedia();
                 }
-            }));
+            }, this::handleError));
     }
 
     /**
@@ -181,7 +368,6 @@ private void findNonHiddenCategories(Media media) {
         updateImage(media);
     }
 
-    @SuppressLint("CheckResult")
     private void updateImage(Media media) {
         reviewHelper.addViewedImagesToDB(media.getPageId());
         this.media = media;
@@ -191,27 +377,26 @@ private void updateImage(Media media) {
             return;
         }
 
-        //If The Media User and Current Session Username is same then Skip the Image
         if (media.getUser() != null && media.getUser().equals(AccountUtil.getUserName(getApplicationContext()))) {
-            runRandomizer();
+            processNextCachedMedia();
             return;
         }
 
         binding.reviewImageView.setImageURI(media.getImageUrl());
 
-        reviewController.onImageRefreshed(media); //file name is updated
+        reviewController.onImageRefreshed(media);
         compositeDisposable.add(reviewHelper.getFirstRevisionOfFile(fileName)
-                .subscribeOn(Schedulers.io())
-                .observeOn(AndroidSchedulers.mainThread())
-                .subscribe(revision -> {
-                    reviewController.firstRevision = revision;
-                    reviewPagerAdapter.updateFileInformation();
-                    @SuppressLint({"StringFormatInvalid", "LocalSuppress"}) String caption = String.format(getString(R.string.review_is_uploaded_by), fileName, revision.getUser());
-                    binding.tvImageCaption.setText(caption);
-                    binding.pbReviewImage.setVisibility(View.GONE);
-                    reviewImageFragment = getInstanceOfReviewImageFragment();
-                    reviewImageFragment.enableButtons();
-                }));
+            .subscribeOn(Schedulers.io())
+            .observeOn(AndroidSchedulers.mainThread())
+            .subscribe(revision -> {
+                reviewController.firstRevision = revision;
+                reviewPagerAdapter.updateFileInformation();
+                String caption = String.format(getString(R.string.review_is_uploaded_by), fileName, revision.getUser());
+                binding.tvImageCaption.setText(caption);
+                binding.pbReviewImage.setVisibility(View.GONE);
+                reviewImageFragment = getInstanceOfReviewImageFragment();
+                reviewImageFragment.enableButtons();
+            }, this::handleError));
         binding.viewPagerReview.setCurrentItem(0);
     }
 
@@ -258,6 +443,21 @@ public void showReviewImageInfo() {
                 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);
+    }
 
 
     @Override