feat: backoff, sync 1 playlist, keep half-gotten playlists

jukebox/src/main/java/at/lockstep/jukebox/DefaultPlaylistRepository.java

@@ -9,6 +9,7 @@ import androidx.lifecycle.Transformations;
 import at.lockstep.jukebox.api.LockstepApiException;
 import at.lockstep.jukebox.api.PlaylistRemoteClient;
 import at.lockstep.jukebox.api.PlaylistRetrofitApi;
+import at.lockstep.jukebox.api.RetryOnRateLimitInterceptor;
 import at.lockstep.jukebox.db.JukeboxDatabase;
 import at.lockstep.jukebox.db.PlaylistDao;
 import at.lockstep.jukebox.db.PlaylistImageEntity;
@@ -65,6 +66,11 @@ public final class DefaultPlaylistRepository implements PlaylistRepository {
         syncCoordinator.syncDelta(retainRemovedPlaylists);
     }
 
+    @Override
+    public void syncPlaylistDetail(@NonNull String playlistId) throws IOException, LockstepApiException {
+        syncCoordinator.syncPlaylistDetail(playlistId);
+    }
+
     @Override
     @NonNull
     public LiveData<List<PlaylistSummary>> observePlaylists() {
@@ -161,6 +167,7 @@ public final class DefaultPlaylistRepository implements PlaylistRepository {
                 .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
                 .create();
         okhttp3.OkHttpClient okHttp = new okhttp3.OkHttpClient.Builder()
+                .addInterceptor(new RetryOnRateLimitInterceptor())
                 .addInterceptor(authInterceptor)
                 .build();
         Retrofit retrofit = new Retrofit.Builder()

jukebox/src/main/java/at/lockstep/jukebox/PlaylistRepository.java

@@ -16,6 +16,11 @@ public interface PlaylistRepository {
 
     void syncDelta(boolean retainRemovedPlaylists) throws IOException, LockstepApiException;
 
+    /**
+     * Fetches full playlist JSON for one id and replaces cached rows for that playlist only.
+     */
+    void syncPlaylistDetail(@NonNull String playlistId) throws IOException, LockstepApiException;
+
     @NonNull
     LiveData<List<PlaylistSummary>> observePlaylists();
 

jukebox/src/main/java/at/lockstep/jukebox/api/RetryOnRateLimitInterceptor.java

@@ -0,0 +1,99 @@
+package at.lockstep.jukebox.api;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import java.io.IOException;
+import java.util.concurrent.ThreadLocalRandom;
+
+import okhttp3.Interceptor;
+import okhttp3.Request;
+import okhttp3.Response;
+
+/**
+ * Retries idempotent GET requests on HTTP 429 and 503 with exponential backoff, optional jitter,
+ * and {@code Retry-After} (seconds) when the server sends it. Helps when Lockstep proxies Spotify
+ * and inherits rate limits.
+ */
+public final class RetryOnRateLimitInterceptor implements Interceptor {
+
+    private final int maxRetries;
+    private final long initialBackoffMs;
+    private final double backoffMultiplier;
+    private final long maxBackoffMs;
+
+    public RetryOnRateLimitInterceptor() {
+        // Spotify / Lockstep can stay hot after bulk sync; extra attempts + longer cap help pairing-on-demand.
+        this(8, 1000L, 2.0, 120_000L);
+    }
+
+    public RetryOnRateLimitInterceptor(
+            int maxRetries,
+            long initialBackoffMs,
+            double backoffMultiplier,
+            long maxBackoffMs
+    ) {
+        this.maxRetries = maxRetries;
+        this.initialBackoffMs = initialBackoffMs;
+        this.backoffMultiplier = backoffMultiplier;
+        this.maxBackoffMs = maxBackoffMs;
+    }
+
+    @NonNull
+    @Override
+    public Response intercept(@NonNull Chain chain) throws IOException {
+        Request request = chain.request();
+        if (!"GET".equalsIgnoreCase(request.method())) {
+            return chain.proceed(request);
+        }
+
+        long backoffMs = initialBackoffMs;
+        Response response = chain.proceed(request);
+        for (int retry = 0; retry <= maxRetries; retry++) {
+            if (response.code() != 429 && response.code() != 503) {
+                return response;
+            }
+            if (retry == maxRetries) {
+                return response;
+            }
+            long retryAfterMs = parseRetryAfterMs(response.header("Retry-After"));
+            long waitMs = Math.max(backoffMs, retryAfterMs);
+            response.close();
+            sleepWithJitter(waitMs);
+            backoffMs = Math.min((long) (backoffMs * backoffMultiplier), maxBackoffMs);
+            response = chain.proceed(request);
+        }
+        return response;
+    }
+
+    private void sleepWithJitter(long baseMs) throws IOException {
+        if (baseMs <= 0) {
+            return;
+        }
+        long jitter = baseMs > 4 ? ThreadLocalRandom.current().nextLong(0, baseMs / 4) : 0L;
+        try {
+            Thread.sleep(baseMs + jitter);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new IOException("interrupted during rate-limit backoff", e);
+        }
+    }
+
+    /**
+     * Parses {@code Retry-After} as a delay in seconds (Spotify / many proxies use this form).
+     * HTTP-date form is not parsed; returns 0 so exponential backoff applies alone.
+     */
+    private static long parseRetryAfterMs(@Nullable String header) {
+        if (header == null || header.isEmpty()) {
+            return 0L;
+        }
+        try {
+            long seconds = Long.parseLong(header.trim());
+            if (seconds > 0) {
+                return Math.min(seconds * 1000L, 300_000L);
+            }
+        } catch (NumberFormatException ignored) {
+        }
+        return 0L;
+    }
+}

jukebox/src/main/java/at/lockstep/jukebox/map/PlaylistMappers.java

@@ -1,5 +1,7 @@
 package at.lockstep.jukebox.map;
 
+import android.util.Log;
+
 import androidx.annotation.NonNull;
 
 import at.lockstep.jukebox.api.dto.ArtistDto;
@@ -24,6 +26,8 @@ import java.util.Map;
  */
 public final class PlaylistMappers {
 
+    private static final String TAG = "JukeboxPlaylist";
+
     private PlaylistMappers() {
     }
 
@@ -60,15 +64,22 @@ public final class PlaylistMappers {
 
     /**
      * Maps the playlist metadata from a full playlist response to a {@link PlaylistEntity} row.
+     * Empty or whitespace-only {@code name} becomes {@code "Untitled playlist"} and is logged for debugging.
      */
     @NonNull
     public static PlaylistEntity toPlaylistEntity(@NonNull FullPlaylistDto dto) {
         String tracksHref = dto.tracks != null ? dto.tracks.href : null;
         Integer tracksTotal = dto.tracks != null ? dto.tracks.total : null;
+        String rawName = dto.name;
+        boolean unnamed = rawName == null || rawName.trim().isEmpty();
+        String displayName = unnamed ? "Untitled playlist" : rawName;
+        if (unnamed) {
+            Log.i(TAG, "Playlist has empty name, id=" + dto.id);
+        }
         return new PlaylistEntity(
                 dto.id,
                 dto.description,
-                dto.name,
+                displayName,
                 dto.primaryColor,
                 dto.snapshotId,
                 tracksHref,

jukebox/src/main/java/at/lockstep/jukebox/sync/SyncCoordinator.java

@@ -25,8 +25,8 @@ import java.util.concurrent.Future;
 
 /**
  * Orchestrates loading playlist metadata from {@link LockstepPlaylistClient} and writing it into
- * {@link PlaylistDao}: full initial import (clear + fetch all details) and incremental sync using
- * {@code snapshot_id} from the playlist list endpoint. Individual playlists are always replaced
+ * {@link PlaylistDao}: full initial import (fetch all details, then clear + replace) and incremental
+ * sync using {@code snapshot_id} from the playlist list endpoint. Individual playlists are always replaced
  * wholesale (images, memberships, and tracks for that playlist) inside a single DAO transaction.
  * <p>
  * Network detail fetches run in parallel up to the pool size passed to
@@ -54,24 +54,25 @@ public final class SyncCoordinator {
 
     /**
      * Same as {@link #SyncCoordinator(PlaylistDao, LockstepPlaylistClient, int)} with parallel detail
-     * concurrency of {@code 6}.
+     * concurrency of {@code 3} to reduce burst traffic against Spotify via the Lockstep API.
      */
     public SyncCoordinator(@NonNull PlaylistDao dao, @NonNull LockstepPlaylistClient remote) {
-        this(dao, remote, 6);
+        this(dao, remote, 3);
     }
 
     /**
-     * Clears all local cache tables, fetches every playlist id from the list endpoint, loads each full
-     * playlist, and persists them. Use for first-time or “reset” sync.
+     * Fetches every playlist id from the list endpoint, loads each full playlist, then clears local
+     * cache tables and persists the new snapshot. Network I/O happens before {@link PlaylistDao#clearAllTables()}
+     * so a failed import (e.g. HTTP 429 mid-way) does not leave the UI with an empty cache.
      */
     public void syncInitial() throws IOException, LockstepApiException {
-        dao.clearAllTables();
         List<SimplifiedPlaylistDto> summaries = remote.fetchPlaylistSummaries();
         List<String> ids = new ArrayList<>(summaries.size());
         for (SimplifiedPlaylistDto s : summaries) {
             ids.add(s.id);
         }
         List<FullPlaylistDto> details = fetchDetailsParallel(ids);
+        dao.clearAllTables();
         for (FullPlaylistDto detail : details) {
             persistFullPlaylist(detail);
         }
@@ -157,6 +158,15 @@ public final class SyncCoordinator {
         }
     }
 
+    /**
+     * Fetches {@code GET /playlists/{playlistId}} and replaces cached images, tracks, and memberships for
+     * that playlist only. Use when the playlist header exists locally but track rows are missing.
+     */
+    public void syncPlaylistDetail(@NonNull String playlistId) throws IOException, LockstepApiException {
+        FullPlaylistDto detail = remote.fetchPlaylistDetail(playlistId);
+        persistFullPlaylist(detail);
+    }
+
     /**
      * Maps {@code detail} to entities and runs {@link PlaylistDao#replacePlaylistContent} for that playlist.
      */