minstrel/flutter_client/lib/cache/metadata_prefetcher.dart

import 'package:flutter/foundation.dart' show debugPrint;
import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../library/library_providers.dart';
import '../models/home_data.dart';

/// Pre-warms the drift cache for entities the user is most likely to
/// tap. The home prefetch fires when /api/home returns. Library
/// tabs and artist detail expose `warmAlbums` / `warmArtists` so they
/// can fan out reads from their own AsyncNotifier callbacks.
///
/// All reads are unawaited and idempotent — providers that already
/// have a cached value short-circuit. Readers/writers don't conflict
/// because each provider de-duplicates concurrent subscribers.
class MetadataPrefetcher {
  MetadataPrefetcher(this._ref) {
    _ref.listen<AsyncValue<HomeData>>(homeProvider, (_, next) {
      next.whenData(_warmHome);
    });
  }

  final Ref _ref;

  /// Cap per section so a 50-album recently-added row doesn't fan
  /// out 50 fetches the moment the screen appears. Top-N covers what
  /// the user can see without scrolling on a typical phone.
  static const _topN = 8;

  /// Pre-warm drift for each album id (no-op past the first dedup).
  /// Called from the library Albums tab + artist detail album grid.
  void warmAlbums(Iterable<String> ids) {
    var n = 0;
    for (final id in ids) {
      if (id.isEmpty) continue;
      if (n++ >= _topN) break;
      _swallow(_ref.read(albumProvider(id).future));
    }
    if (n > 0) debugPrint('metadataPrefetcher: warming $n albums');
  }

  /// Pre-warm drift for each artist id.
  void warmArtists(Iterable<String> ids) {
    var n = 0;
    for (final id in ids) {
      if (id.isEmpty) continue;
      if (n++ >= _topN) break;
      _swallow(_ref.read(artistProvider(id).future));
    }
    if (n > 0) debugPrint('metadataPrefetcher: warming $n artists');
  }

  void _warmHome(HomeData h) {
    final albumIds = <String>{};
    final artistIds = <String>{};

    for (final a in h.recentlyAddedAlbums.take(_topN)) {
      if (a.id.isNotEmpty) albumIds.add(a.id);
      if (a.artistId.isNotEmpty) artistIds.add(a.artistId);
    }
    for (final a in h.rediscoverAlbums.take(_topN)) {
      if (a.id.isNotEmpty) albumIds.add(a.id);
      if (a.artistId.isNotEmpty) artistIds.add(a.artistId);
    }
    for (final ar in h.rediscoverArtists.take(_topN)) {
      if (ar.id.isNotEmpty) artistIds.add(ar.id);
    }
    for (final ar in h.lastPlayedArtists.take(_topN)) {
      if (ar.id.isNotEmpty) artistIds.add(ar.id);
    }
    for (final t in h.mostPlayedTracks.take(_topN)) {
      if (t.albumId.isNotEmpty) albumIds.add(t.albumId);
      if (t.artistId.isNotEmpty) artistIds.add(t.artistId);
    }

    debugPrint(
        'metadataPrefetcher: warming ${albumIds.length} albums + ${artistIds.length} artists');

    for (final id in albumIds) {
      _swallow(_ref.read(albumProvider(id).future));
    }
    for (final id in artistIds) {
      _swallow(_ref.read(artistProvider(id).future));
    }
  }

  /// Discards the return value and any error from a fire-and-forget
  /// provider read. We don't care about the value here — we only want
  /// the side effect of writing drift.
  void _swallow(Future<Object?> f) {
    f.then<void>((_) {}).onError((_, __) {});
  }
}

/// Read once at app start to activate the prefetcher (e.g. wire it
/// from a top-level Consumer or main.dart container override).
final metadataPrefetcherProvider = Provider<MetadataPrefetcher>((ref) {
  return MetadataPrefetcher(ref);
});