Nicer placeholder images (#5679)

Shows randomly generated placeholder images for:

- Feeds that do not have a cover (usually happens for text-only feeds)
  - Feeds that specify an invalid cover still show a gray square
- Local folders when there is no image file in the folder that we could use

8 files changed, 161 insertions, 32 deletions

diff --git a/app/src/main/java/de/danoeh/antennapod/adapter/SubscriptionsRecyclerAdapter.java b/app/src/main/java/de/danoeh/antennapod/adapter/SubscriptionsRecyclerAdapter.java
index 5ab354d05..8351d1fb5 100644
--- a/app/src/main/java/de/danoeh/antennapod/adapter/SubscriptionsRecyclerAdapter.java
+++ b/app/src/main/java/de/danoeh/antennapod/adapter/SubscriptionsRecyclerAdapter.java
@@ -33,7 +33,6 @@ import java.util.Locale;
 
 import de.danoeh.antennapod.R;
 import de.danoeh.antennapod.activity.MainActivity;
-import de.danoeh.antennapod.core.feed.LocalFeedUpdater;
 import de.danoeh.antennapod.core.preferences.UserPreferences;
 import de.danoeh.antennapod.core.storage.NavDrawerData;
 import de.danoeh.antennapod.fragment.FeedItemlistFragment;
@@ -255,7 +254,7 @@ public class SubscriptionsRecyclerAdapter extends SelectableAdapter<Subscription
             if (drawerItem.type == NavDrawerData.DrawerItem.Type.FEED) {
                 Feed feed = ((NavDrawerData.FeedDrawerItem) drawerItem).feed;
                 boolean textAndImageCombind = feed.isLocalFeed()
-                        && LocalFeedUpdater.getDefaultIconUrl(itemView.getContext()).equals(feed.getImageUrl());
+                        && feed.getImageUrl() != null && feed.getImageUrl().startsWith(Feed.PREFIX_GENERATIVE_COVER);
                 new CoverLoader(mainActivityRef.get())
                         .withUri(feed.getImageUrl())
                         .withPlaceholderView(feedTitle, textAndImageCombind)
diff --git a/core/src/main/java/de/danoeh/antennapod/core/feed/LocalFeedUpdater.java b/core/src/main/java/de/danoeh/antennapod/core/feed/LocalFeedUpdater.java
index 7ddaa080a..e0e1bbaa5 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/feed/LocalFeedUpdater.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/feed/LocalFeedUpdater.java
@@ -1,6 +1,5 @@
 package de.danoeh.antennapod.core.feed;
 
-import android.content.ContentResolver;
 import android.content.Context;
 import android.media.MediaMetadataRetriever;
 import android.net.Uri;
@@ -104,7 +103,7 @@ public class LocalFeedUpdater {
             }
         }
 
-        feed.setImageUrl(getImageUrl(context, documentFolder));
+        feed.setImageUrl(getImageUrl(documentFolder));
 
         feed.getPreferences().setAutoDownload(false);
         feed.getPreferences().setAutoDeleteAction(FeedPreferences.AutoDeleteAction.NO);
@@ -122,7 +121,7 @@ public class LocalFeedUpdater {
      * Returns the image URL for the local feed.
      */
     @NonNull
-    static String getImageUrl(@NonNull Context context, @NonNull DocumentFile documentFolder) {
+    static String getImageUrl(@NonNull DocumentFile documentFolder) {
         // look for special file names
         for (String iconLocation : PREFERRED_FEED_IMAGE_FILENAMES) {
             DocumentFile image = documentFolder.findFile(iconLocation);
@@ -140,17 +139,7 @@ public class LocalFeedUpdater {
         }
 
         // use default icon as fallback
-        return getDefaultIconUrl(context);
-    }
-
-    /**
-     * Returns the URL of the default icon for a local feed. The URL refers to an app resource file.
-     */
-    public static String getDefaultIconUrl(Context context) {
-        String resourceEntryName = context.getResources().getResourceEntryName(R.raw.local_feed_default_icon);
-        return ContentResolver.SCHEME_ANDROID_RESOURCE + "://"
-                + context.getPackageName() + "/raw/"
-                + resourceEntryName;
+        return Feed.PREFIX_GENERATIVE_COVER + documentFolder.getUri();
     }
 
     private static FeedItem feedContainsFile(Feed feed, String filename) {
diff --git a/core/src/main/java/de/danoeh/antennapod/core/glide/ApGlideModule.java b/core/src/main/java/de/danoeh/antennapod/core/glide/ApGlideModule.java
index 797addcc1..593b683f7 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/glide/ApGlideModule.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/glide/ApGlideModule.java
@@ -42,6 +42,7 @@ public class ApGlideModule extends AppGlideModule {
     @Override
     public void registerComponents(@NonNull Context context, @NonNull Glide glide, @NonNull Registry registry) {
         registry.replace(String.class, InputStream.class, new MetadataRetrieverLoader.Factory(context));
+        registry.append(String.class, InputStream.class, new GenerativePlaceholderImageModelLoader.Factory());
         registry.append(String.class, InputStream.class, new ApOkHttpUrlLoader.Factory());
         registry.append(String.class, InputStream.class, new NoHttpStringLoader.StreamFactory());
 
diff --git a/core/src/main/java/de/danoeh/antennapod/core/glide/GenerativePlaceholderImageModelLoader.java b/core/src/main/java/de/danoeh/antennapod/core/glide/GenerativePlaceholderImageModelLoader.java
new file mode 100644
index 000000000..a2263bc28
--- /dev/null
+++ b/core/src/main/java/de/danoeh/antennapod/core/glide/GenerativePlaceholderImageModelLoader.java
@@ -0,0 +1,139 @@
+package de.danoeh.antennapod.core.glide;
+
+import android.graphics.Bitmap;
+import android.graphics.Canvas;
+import android.graphics.LinearGradient;
+import android.graphics.Paint;
+import android.graphics.PorterDuff;
+import android.graphics.PorterDuffColorFilter;
+import android.graphics.Shader;
+import androidx.annotation.NonNull;
+import com.bumptech.glide.Priority;
+import com.bumptech.glide.load.DataSource;
+import com.bumptech.glide.load.Options;
+import com.bumptech.glide.load.data.DataFetcher;
+import com.bumptech.glide.load.model.ModelLoader;
+import com.bumptech.glide.load.model.ModelLoaderFactory;
+import com.bumptech.glide.load.model.MultiModelLoaderFactory;
+import com.bumptech.glide.signature.ObjectKey;
+import de.danoeh.antennapod.model.feed.Feed;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.InputStream;
+import java.util.Random;
+
+public final class GenerativePlaceholderImageModelLoader implements ModelLoader<String, InputStream> {
+
+    public static class Factory implements ModelLoaderFactory<String, InputStream> {
+        @NonNull
+        @Override
+        public ModelLoader<String, InputStream> build(@NonNull MultiModelLoaderFactory unused) {
+            return new GenerativePlaceholderImageModelLoader();
+        }
+
+        @Override
+        public void teardown() {
+            // Do nothing.
+        }
+    }
+
+    @Override
+    public LoadData<InputStream> buildLoadData(@NonNull String model, int width, int height, @NonNull Options options) {
+        return new LoadData<>(new ObjectKey(model), new EmbeddedImageFetcher(model, width, height));
+    }
+
+    @Override
+    public boolean handles(@NonNull String model) {
+        return model.startsWith(Feed.PREFIX_GENERATIVE_COVER);
+    }
+
+    static class EmbeddedImageFetcher implements DataFetcher<InputStream> {
+        private static final int[] PALETTES = {0xff78909c, 0xffff6f00, 0xff388e3c,
+                0xff00838f, 0xff7b1fa2, 0xffb71c1c, 0xff2196f3};
+        private final String model;
+        private final int width;
+        private final int height;
+
+        public EmbeddedImageFetcher(String model, int width, int height) {
+            this.model = model;
+            this.width = width;
+            this.height = height;
+        }
+
+        @Override
+        public void loadData(@NonNull Priority priority, @NonNull DataCallback<? super InputStream> callback) {
+            final Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
+            final Canvas canvas = new Canvas(bitmap);
+            final Random generator = new Random(model.hashCode());
+            final int lineGridSteps = 4 + generator.nextInt(4);
+            final int slope = width / 4;
+            final float shadowWidth = width * 0.01f;
+            final float lineDistance = ((float) width / (lineGridSteps - 2));
+            final int baseColor = PALETTES[generator.nextInt(PALETTES.length)];
+
+            Paint paint = new Paint();
+            int color = randomShadeOfGrey(generator);
+            paint.setColor(color);
+            paint.setStrokeWidth(lineDistance);
+            paint.setColorFilter(new PorterDuffColorFilter(baseColor, PorterDuff.Mode.MULTIPLY));
+            Paint paintShadow = new Paint();
+            paintShadow.setColor(0xff000000);
+            paintShadow.setStrokeWidth(lineDistance);
+
+            int forcedColorChange = 1 + generator.nextInt(lineGridSteps - 2);
+            for (int i = lineGridSteps - 1; i >= 0; i--) {
+                float linePos = (i - 0.5f) * lineDistance;
+                boolean switchColor = generator.nextFloat() < 0.3f || i == forcedColorChange;
+                if (switchColor) {
+                    int newColor = color;
+                    while (newColor == color) {
+                        newColor = randomShadeOfGrey(generator);
+                    }
+                    color = newColor;
+                    paint.setColor(newColor);
+                    canvas.drawLine(linePos + slope + shadowWidth, -slope,
+                            linePos - slope + shadowWidth, height + slope, paintShadow);
+                }
+                canvas.drawLine(linePos + slope, -slope,
+                        linePos - slope, height + slope, paint);
+            }
+
+            Paint gradientPaint = new Paint();
+            paint.setDither(true);
+            gradientPaint.setShader(new LinearGradient(0, 0, 0, height, 0x00000000, 0x55000000, Shader.TileMode.CLAMP));
+            canvas.drawRect(0, 0, width, height, gradientPaint);
+
+            ByteArrayOutputStream baos = new ByteArrayOutputStream();
+            bitmap.compress(Bitmap.CompressFormat.JPEG, 100, baos);
+            InputStream is = new ByteArrayInputStream(baos.toByteArray());
+            callback.onDataReady(is);
+        }
+
+        private static int randomShadeOfGrey(Random generator) {
+            return 0xff777777 + 0x222222 * generator.nextInt(5);
+        }
+
+        @Override
+        public void cleanup() {
+            // nothing to clean up
+        }
+
+        @Override
+        public void cancel() {
+            // cannot cancel
+        }
+
+        @NonNull
+        @Override
+        public Class<InputStream> getDataClass() {
+            return InputStream.class;
+        }
+
+        @NonNull
+        @Override
+        public DataSource getDataSource() {
+            return DataSource.LOCAL;
+        }
+    }
+}
diff --git a/core/src/main/java/de/danoeh/antennapod/core/service/download/handler/FeedParserTask.java b/core/src/main/java/de/danoeh/antennapod/core/service/download/handler/FeedParserTask.java
index 21d3452d6..7e3b07880 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/service/download/handler/FeedParserTask.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/service/download/handler/FeedParserTask.java
@@ -1,5 +1,6 @@
 package de.danoeh.antennapod.core.service.download.handler;
 
+import android.text.TextUtils;
 import android.util.Log;
 import de.danoeh.antennapod.model.feed.Feed;
 import de.danoeh.antennapod.model.feed.FeedItem;
@@ -48,6 +49,9 @@ public class FeedParserTask implements Callable<FeedHandlerResult> {
             result = feedHandler.parseFeed(feed);
             Log.d(TAG, feed.getTitle() + " parsed");
             checkFeedData(feed);
+            if (TextUtils.isEmpty(feed.getImageUrl())) {
+                feed.setImageUrl(Feed.PREFIX_GENERATIVE_COVER + feed.getDownload_url());
+            }
         } catch (SAXException | IOException | ParserConfigurationException e) {
             successful = false;
             e.printStackTrace();
diff --git a/core/src/main/res/raw/local_feed_default_icon.png b/core/src/main/res/raw/local_feed_default_icon.png
deleted file mode 100644
index c1b24a729..000000000
--- a/core/src/main/res/raw/local_feed_default_icon.png
+++ /dev/null
diff --git a/core/src/test/java/de/danoeh/antennapod/core/feed/LocalFeedUpdaterTest.java b/core/src/test/java/de/danoeh/antennapod/core/feed/LocalFeedUpdaterTest.java
index eb56a1876..37d525670 100644
--- a/core/src/test/java/de/danoeh/antennapod/core/feed/LocalFeedUpdaterTest.java
+++ b/core/src/test/java/de/danoeh/antennapod/core/feed/LocalFeedUpdaterTest.java
@@ -31,7 +31,6 @@ import java.util.List;
 
 import de.danoeh.antennapod.core.ApplicationCallbacks;
 import de.danoeh.antennapod.core.ClientConfig;
-import de.danoeh.antennapod.core.R;
 import de.danoeh.antennapod.core.preferences.UserPreferences;
 import de.danoeh.antennapod.core.storage.DBReader;
 import de.danoeh.antennapod.core.storage.DBWriter;
@@ -41,6 +40,7 @@ import static org.hamcrest.CoreMatchers.endsWith;
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.empty;
+import static org.hamcrest.Matchers.startsWith;
 import static org.junit.Assert.assertEquals;
 import static org.mockito.Mockito.any;
 import static org.mockito.Mockito.mock;
@@ -158,8 +158,7 @@ public class LocalFeedUpdaterTest {
         callUpdateFeed(LOCAL_FEED_DIR1);
 
         Feed feedAfter = verifySingleFeedInDatabase();
-        String resourceEntryName = context.getResources().getResourceEntryName(R.raw.local_feed_default_icon);
-        assertThat(feedAfter.getImageUrl(), endsWith(resourceEntryName));
+        assertThat(feedAfter.getImageUrl(), startsWith(Feed.PREFIX_GENERATIVE_COVER));
     }
 
     /**
@@ -191,17 +190,15 @@ public class LocalFeedUpdaterTest {
     @Test
     public void testGetImageUrl_EmptyFolder() {
         DocumentFile documentFolder = mockDocumentFolder();
-        String imageUrl = LocalFeedUpdater.getImageUrl(context, documentFolder);
-        String defaultImageName = context.getResources().getResourceEntryName(R.raw.local_feed_default_icon);
-        assertThat(imageUrl, endsWith(defaultImageName));
+        String imageUrl = LocalFeedUpdater.getImageUrl(documentFolder);
+        assertThat(imageUrl, startsWith(Feed.PREFIX_GENERATIVE_COVER));
     }
 
     @Test
     public void testGetImageUrl_NoImageButAudioFiles() {
         DocumentFile documentFolder = mockDocumentFolder(mockDocumentFile("audio.mp3", "audio/mp3"));
-        String imageUrl = LocalFeedUpdater.getImageUrl(context, documentFolder);
-        String defaultImageName = context.getResources().getResourceEntryName(R.raw.local_feed_default_icon);
-        assertThat(imageUrl, endsWith(defaultImageName));
+        String imageUrl = LocalFeedUpdater.getImageUrl(documentFolder);
+        assertThat(imageUrl, startsWith(Feed.PREFIX_GENERATIVE_COVER));
     }
 
     @Test
@@ -209,7 +206,7 @@ public class LocalFeedUpdaterTest {
         for (String filename : LocalFeedUpdater.PREFERRED_FEED_IMAGE_FILENAMES) {
             DocumentFile documentFolder = mockDocumentFolder(mockDocumentFile("audio.mp3", "audio/mp3"),
                     mockDocumentFile(filename, "image/jpeg")); // image MIME type doesn't matter
-            String imageUrl = LocalFeedUpdater.getImageUrl(context, documentFolder);
+            String imageUrl = LocalFeedUpdater.getImageUrl(documentFolder);
             assertThat(imageUrl, endsWith(filename));
         }
     }
@@ -218,7 +215,7 @@ public class LocalFeedUpdaterTest {
     public void testGetImageUrl_OtherImageFilenameJpg() {
         DocumentFile documentFolder = mockDocumentFolder(mockDocumentFile("audio.mp3", "audio/mp3"),
                 mockDocumentFile("my-image.jpg", "image/jpeg"));
-        String imageUrl = LocalFeedUpdater.getImageUrl(context, documentFolder);
+        String imageUrl = LocalFeedUpdater.getImageUrl(documentFolder);
         assertThat(imageUrl, endsWith("my-image.jpg"));
     }
 
@@ -226,7 +223,7 @@ public class LocalFeedUpdaterTest {
     public void testGetImageUrl_OtherImageFilenameJpeg() {
         DocumentFile documentFolder = mockDocumentFolder(mockDocumentFile("audio.mp3", "audio/mp3"),
                 mockDocumentFile("my-image.jpeg", "image/jpeg"));
-        String imageUrl = LocalFeedUpdater.getImageUrl(context, documentFolder);
+        String imageUrl = LocalFeedUpdater.getImageUrl(documentFolder);
         assertThat(imageUrl, endsWith("my-image.jpeg"));
     }
 
@@ -234,7 +231,7 @@ public class LocalFeedUpdaterTest {
     public void testGetImageUrl_OtherImageFilenamePng() {
         DocumentFile documentFolder = mockDocumentFolder(mockDocumentFile("audio.mp3", "audio/mp3"),
                 mockDocumentFile("my-image.png", "image/png"));
-        String imageUrl = LocalFeedUpdater.getImageUrl(context, documentFolder);
+        String imageUrl = LocalFeedUpdater.getImageUrl(documentFolder);
         assertThat(imageUrl, endsWith("my-image.png"));
     }
 
@@ -242,9 +239,8 @@ public class LocalFeedUpdaterTest {
     public void testGetImageUrl_OtherImageFilenameUnsupportedMimeType() {
         DocumentFile documentFolder = mockDocumentFolder(mockDocumentFile("audio.mp3", "audio/mp3"),
                 mockDocumentFile("my-image.svg", "image/svg+xml"));
-        String imageUrl = LocalFeedUpdater.getImageUrl(context, documentFolder);
-        String defaultImageName = context.getResources().getResourceEntryName(R.raw.local_feed_default_icon);
-        assertThat(imageUrl, endsWith(defaultImageName));
+        String imageUrl = LocalFeedUpdater.getImageUrl(documentFolder);
+        assertThat(imageUrl, startsWith(Feed.PREFIX_GENERATIVE_COVER));
     }
 
     /**
diff --git a/model/src/main/java/de/danoeh/antennapod/model/feed/Feed.java b/model/src/main/java/de/danoeh/antennapod/model/feed/Feed.java
index e570f9bce..006505eb1 100644
--- a/model/src/main/java/de/danoeh/antennapod/model/feed/Feed.java
+++ b/model/src/main/java/de/danoeh/antennapod/model/feed/Feed.java
@@ -19,6 +19,7 @@ public class Feed extends FeedFile {
     public static final String TYPE_RSS2 = "rss";
     public static final String TYPE_ATOM1 = "atom";
     public static final String PREFIX_LOCAL_FOLDER = "antennapod_local:";
+    public static final String PREFIX_GENERATIVE_COVER = "antennapod_generative_cover:";
 
     /**
      * title as defined by the feed.