import 'dart:async';
import '../media/ids.dart';

import '../media/media_hub.dart';
import '../media/media_item.dart';
import '../media/media_kind.dart';
import '../media/media_library.dart';
import '../media/media_server_client.dart';
import '../exceptions/media_server_exceptions.dart';
import '../utils/app_logger.dart';
import '../utils/external_ids.dart';
import '../utils/global_key_utils.dart';
import '../utils/search_relevance.dart';
import 'local_playback_history.dart';
import 'multi_server_manager.dart';

typedef OnDeckAggregationResult = ({
  List<MediaItem> items,
  Set<String> succeededServerIds,
  Set<String> cancelledServerIds,
});
typedef HubAggregationResult = ({List<MediaHub> hubs, Set<String> succeededServerIds, Set<String> cancelledServerIds});
typedef LibraryAggregationResult = ({
  List<MediaLibrary> libraries,
  Set<String> succeededServerIds,
  Set<String> cancelledServerIds,
});
typedef _FanOutResult<T> = ({List<T> items, Set<String> succeededServerIds, Set<String> cancelledServerIds});

/// Whether [error] is a client-side abort (client teardown mid-request)
/// rather than a genuine server failure. Aggregation reports these servers
/// in `cancelledServerIds` so callers can tell a *disrupted* pass — whose
/// results say nothing about actual content — from a settled failure.
bool _isCancellation(Object error) => error is MediaServerHttpException && error.isCancellation;

/// Cross-server aggregation: fans calls out to every online client and
/// merges the results. Single-server operations now go through the
/// [MediaServerClient] interface directly (resolved via
/// [ProviderExtensions.tryGetMediaClientForServer] etc.), so this service
/// only owns the genuinely multi-server flows: home/discover hubs, on-deck,
/// search, and the global library list.
class DataAggregationService {
  final MultiServerManager _serverManager;

  DataAggregationService(this._serverManager);

  /// Online clients, optionally restricted to [serverIds] — delta refreshes
  /// fan out to newly-online servers only.
  Map<String, MediaServerClient> _clientsFor(Set<String>? serverIds) {
    final clients = _serverManager.onlineClients;
    if (serverIds == null) return clients;
    return {
      for (final entry in clients.entries)
        if (serverIds.contains(entry.key)) entry.key: entry.value,
    };
  }

  /// Run [fetch] against every client in [clients] and concatenate the results
  /// in client order. A per-server failure is swallowed — logged with
  /// [failureMessage] and contributing nothing — so one bad server cannot sink
  /// the pass; that server is simply absent from `succeededServerIds`, and also
  /// lands in `cancelledServerIds` when the failure was a client-side abort.
  Future<_FanOutResult<T>> _fanOut<T>(
    Map<String, MediaServerClient> clients, {
    required String Function(String serverId) failureMessage,
    required Future<List<T>> Function(String serverId, MediaServerClient client) fetch,
  }) async {
    final cancelledServerIds = <String>{};
    final futures = clients.entries.map((entry) async {
      try {
        return (serverId: entry.key, items: await fetch(entry.key, entry.value));
      } catch (e, stackTrace) {
        if (_isCancellation(e)) cancelledServerIds.add(entry.key);
        appLogger.e(failureMessage(entry.key), error: e, stackTrace: stackTrace);
        return (serverId: null, items: <T>[]);
      }
    });
    final results = await Future.wait(futures);
    return (
      items: [for (final result in results) ...result.items],
      succeededServerIds: {
        for (final result in results)
          if (result.serverId != null) result.serverId!,
      },
      cancelledServerIds: cancelledServerIds,
    );
  }

  /// Fetch libraries from all online clients regardless of backend, returning
  /// the merged neutral [MediaLibrary]s alongside the ids of the servers whose
  /// fetch actually succeeded. [serverIds] restricts the fan-out to those
  /// servers.
  ///
  /// A per-server `fetchLibraries()` failure is swallowed (that server simply
  /// contributes no libraries) so one unreachable server doesn't sink the whole
  /// list. [succeededServerIds] lets callers tell a *failed* fetch apart from a
  /// server that genuinely has no libraries — both contribute nothing, so
  /// conflating them would let a transient failure be cached as "loaded" and
  /// never retried. Servers whose fetch was aborted client-side land in
  /// `cancelledServerIds` — a disrupted pass, unlike a settled failure, must
  /// never be committed as authoritative.
  Future<LibraryAggregationResult> getMediaLibrariesFromAllServers({Set<String>? serverIds}) async {
    final clients = _clientsFor(serverIds);
    if (clients.isEmpty) {
      appLogger.w('No online servers available for fetching libraries (neutral)');
      return (
        libraries: const <MediaLibrary>[],
        succeededServerIds: const <String>{},
        cancelledServerIds: const <String>{},
      );
    }
    final fetched = await _fanOut<MediaLibrary>(
      clients,
      failureMessage: (serverId) => 'Failed neutral library fetch from $serverId',
      fetch: (_, client) => client.fetchLibraries(),
    );
    return (
      libraries: fetched.items,
      succeededServerIds: fetched.succeededServerIds,
      cancelledServerIds: fetched.cancelledServerIds,
    );
  }

  /// Fetch "On Deck" (Continue Watching) from all servers and merge by recency.
  /// Items are tagged with server info by the underlying client. Returns
  /// neutral [MediaItem]s plus the ids of servers whose fetch succeeded.
  /// [serverIds] restricts the fan-out to those servers.
  Future<OnDeckAggregationResult> getOnDeckFromAllServers({
    int? limit,
    Set<String>? hiddenLibraryKeys,
    Set<String>? serverIds,
  }) async {
    final clients = _clientsFor(serverIds);
    if (clients.isEmpty) {
      appLogger.w('No online servers available for fetching on deck');
      return (items: const <MediaItem>[], succeededServerIds: const <String>{}, cancelledServerIds: const <String>{});
    }

    final fetched = await _fanOut<MediaItem>(
      clients,
      failureMessage: (serverId) => 'Failed on-deck fetch from $serverId',
      fetch: (_, client) => client.fetchContinueWatching(count: limit),
    );
    final allOnDeck = fetched.items;

    // Filter out items from hidden libraries
    List<MediaItem> filteredOnDeck = allOnDeck;
    if (hiddenLibraryKeys != null && hiddenLibraryKeys.isNotEmpty) {
      filteredOnDeck = allOnDeck.where((item) {
        if (item.libraryId == null || item.serverId == null) return true;
        final globalKey = buildGlobalKey(ServerId(item.serverId!), item.libraryId!);
        return !hiddenLibraryKeys.contains(globalKey);
      }).toList();
    }

    // Sort by most recently viewed, falling back to addedAt for unwatched items.
    // Same key as JellyfinClient's continue-watching merge (MediaItem.recencySortKey)
    // so per-server and cross-server ordering can't drift apart.
    filteredOnDeck.sort((a, b) => b.recencySortKey.compareTo(a.recencySortKey));

    filteredOnDeck = await _deduplicateContinueWatching(filteredOnDeck);

    // Apply limit if specified
    final items = limit != null && limit < filteredOnDeck.length ? filteredOnDeck.sublist(0, limit) : filteredOnDeck;

    appLogger.i('Fetched ${items.length} on deck items from all servers');

    return (
      items: items,
      succeededServerIds: fetched.succeededServerIds,
      cancelledServerIds: fetched.cancelledServerIds,
    );
  }

  /// Merge an [existing] Continue Watching list with [fresh] rows from
  /// newly-online servers: same recency ordering and cross-server identity
  /// dedup as [getOnDeckFromAllServers], applied to the union.
  Future<List<MediaItem>> mergeContinueWatching(List<MediaItem> existing, List<MediaItem> fresh, {int? limit}) async {
    final combined = [...existing, ...fresh]..sort((a, b) => b.recencySortKey.compareTo(a.recencySortKey));
    final deduped = await _deduplicateContinueWatching(combined);
    return limit != null && limit < deduped.length ? deduped.sublist(0, limit) : deduped;
  }

  Future<List<MediaItem>> _deduplicateContinueWatching(List<MediaItem> items) async {
    if (items.length < 2) return items;

    final bucketCounts = <String, int>{};
    for (final item in items) {
      final bucket = _continueWatchingTitleBucket(item);
      if (bucket == null) continue;
      bucketCounts[bucket] = (bucketCounts[bucket] ?? 0) + 1;
    }

    final duplicateBuckets = {
      for (final entry in bucketCounts.entries)
        if (entry.value > 1) entry.key,
    };
    if (duplicateBuckets.isEmpty) return items;

    final externalIdLoads = <String, Future<ExternalIds>>{};
    final identityKeysByIndex = <int, Set<String>>{};
    final identityKeyLoads = <Future<void>>[];
    for (var i = 0; i < items.length; i++) {
      if (!duplicateBuckets.contains(_continueWatchingTitleBucket(items[i]))) continue;
      final index = i;
      identityKeyLoads.add(
        _continueWatchingIdentityKeys(items[index], externalIdLoads).then((keys) => identityKeysByIndex[index] = keys),
      );
    }
    await Future.wait(identityKeyLoads);

    // Group duplicates instead of greedily dropping them: the first item to
    // claim an identity key anchors the group and holds its shelf slot;
    // later items sharing a claimed key join as members without claiming
    // their own keys (same transitive semantics as the old drop). Each slot
    // then shows the member the user most recently played on this device —
    // servers sync watch state across guid-linked siblings, so their
    // lastViewedAt ties and can't tell the 4K copy from the 1080p one
    // (#1492). Without local history the anchor (recency order) stands.
    final keyToGroup = <String, int>{};
    final groups = <List<MediaItem>>[];
    final groupSlots = <int, int>{};
    final result = <MediaItem>[];
    for (var i = 0; i < items.length; i++) {
      final item = items[i];
      if (!duplicateBuckets.contains(_continueWatchingTitleBucket(item))) {
        result.add(item);
        continue;
      }

      final identityKeys = identityKeysByIndex[i] ?? const <String>{};
      if (identityKeys.isEmpty) {
        result.add(item);
        continue;
      }

      var joined = false;
      for (final key in identityKeys) {
        final groupIndex = keyToGroup[key];
        if (groupIndex != null) {
          groups[groupIndex].add(item);
          joined = true;
          break;
        }
      }
      if (joined) continue;

      final groupIndex = groups.length;
      groups.add([item]);
      for (final key in identityKeys) {
        keyToGroup[key] = groupIndex;
      }
      groupSlots[result.length] = groupIndex;
      result.add(item);
    }

    if (groupSlots.isEmpty) return result;
    final lastPlayed = await LocalPlaybackHistory.snapshot();
    for (final slot in groupSlots.entries) {
      final members = groups[slot.value];
      if (members.length > 1) {
        result[slot.key] = _preferLocallyLastPlayed(members, lastPlayed);
      }
    }
    return result;
  }

  /// The duplicate-group member most recently played on this device (by item
  /// or series key), or the anchor — `members.first`, the group's most recent
  /// item by [MediaItem.recencySortKey] — when the local history has nothing
  /// newer to say.
  MediaItem _preferLocallyLastPlayed(List<MediaItem> members, Map<String, int> lastPlayed) {
    var winner = members.first;
    var winnerLastPlayedAt = 0;
    for (final member in members) {
      final itemTs = lastPlayed[member.globalKey] ?? 0;
      final seriesKey = member.seriesGlobalKey;
      final seriesTs = seriesKey != null ? (lastPlayed[seriesKey] ?? 0) : 0;
      final lastPlayedAt = itemTs > seriesTs ? itemTs : seriesTs;
      if (lastPlayedAt > winnerLastPlayedAt) {
        winner = member;
        winnerLastPlayedAt = lastPlayedAt;
      }
    }
    return winner;
  }

  String? _continueWatchingTitleBucket(MediaItem item) {
    final scope = _continueWatchingIdentityScope(item);
    if (scope == null) return null;

    final title = switch (item.kind) {
      MediaKind.episode || MediaKind.season => item.grandparentTitle ?? item.parentTitle ?? item.title,
      _ => item.title,
    };
    final normalized = title?.trim().toLowerCase().replaceAll(RegExp(r'\s+'), ' ');
    if (normalized == null || normalized.isEmpty) return null;
    return '$scope:$normalized';
  }

  Future<Set<String>> _continueWatchingIdentityKeys(
    MediaItem item,
    Map<String, Future<ExternalIds>> externalIdLoads,
  ) async {
    final scope = _continueWatchingIdentityScope(item);
    if (scope == null) return const {};

    final keys = <String>{};
    final serverId = item.serverId;
    final targetId = _continueWatchingIdentityTargetId(item);
    final client = serverId == null ? null : _serverManager.getClient(ServerId(serverId));

    if (client != null && targetId != null && targetId.isNotEmpty) {
      try {
        final cacheKey = buildGlobalKey(ServerId(serverId!), targetId);
        final externalIds = await externalIdLoads.putIfAbsent(cacheKey, () => client.fetchExternalIds(targetId));
        _addExternalIdentityKeys(keys, scope, externalIds);
      } catch (e, stackTrace) {
        appLogger.d(
          'Failed to resolve Continue Watching identity for ${item.globalKey}',
          error: e,
          stackTrace: stackTrace,
        );
      }
    }

    final stableGuid = _stableMediaGuid(item.guid);
    if (stableGuid != null) {
      final guidScope = item.kind == MediaKind.episode ? 'episode' : scope;
      keys.add('$guidScope:guid:$stableGuid');
    }

    return keys;
  }

  String? _continueWatchingIdentityScope(MediaItem item) {
    return switch (item.kind) {
      MediaKind.episode || MediaKind.season || MediaKind.show => 'show',
      MediaKind.movie => 'movie',
      _ => null,
    };
  }

  String? _continueWatchingIdentityTargetId(MediaItem item) {
    return switch (item.kind) {
      MediaKind.episode => item.grandparentId,
      MediaKind.season => item.grandparentId ?? item.parentId,
      MediaKind.show || MediaKind.movie => item.id,
      _ => null,
    };
  }

  void _addExternalIdentityKeys(Set<String> keys, String scope, ExternalIds externalIds) {
    final imdb = externalIds.imdb?.trim().toLowerCase();
    if (imdb != null && imdb.isNotEmpty) keys.add('$scope:imdb:$imdb');
    final tmdb = externalIds.tmdb;
    if (tmdb != null) keys.add('$scope:tmdb:$tmdb');
    final tvdb = externalIds.tvdb;
    if (tvdb != null) keys.add('$scope:tvdb:$tvdb');
  }

  String? _stableMediaGuid(String? guid) {
    final value = guid?.trim();
    if (value == null || value.isEmpty) return null;
    if (!value.contains('://')) return null;
    if (value.contains('agents.none://')) return null;
    return value.toLowerCase();
  }

  /// Fetch recommendation hubs from all servers as neutral [MediaHub]s.
  /// When useGlobalHubs is true (default), rich-hub backends use their true
  /// home page hubs (Plex's promoted/global hub endpoint).
  /// Backends without rich home hubs fall back to per-library hubs so one
  /// capped "Latest" response cannot hide whole library types.
  /// [serverIds] restricts the fan-out (including the library prefetch) to
  /// those servers. Returns the ids of servers whose hub fetch succeeded so
  /// callers do not cache transient per-server failures as loaded.
  Future<HubAggregationResult> getHubsFromAllServers({
    int? limit,
    Set<String>? hiddenLibraryKeys,
    bool useGlobalHubs = true,
    bool includePlaybackHubs = true,
    Set<String>? serverIds,
  }) async {
    final clients = _clientsFor(serverIds);
    if (clients.isEmpty) {
      appLogger.w('No online servers available for fetching hubs');
      return (hubs: const <MediaHub>[], succeededServerIds: const <String>{}, cancelledServerIds: const <String>{});
    }

    // Home layout needs the library list for every client: fallback backends
    // build all their rows from per-library hubs, and rich-hub backends
    // (Plex) need it to detect visible music libraries, whose hubs the
    // global-hub endpoint excludes. One `fetchLibraries` per server, served
    // from the per-backend API cache when warm.
    final libraries = useGlobalHubs
        ? _groupLibrariesByServer((await getMediaLibrariesFromAllServers(serverIds: serverIds)).libraries)
        : null;

    final fetched = await _fanOut<MediaHub>(
      clients,
      failureMessage: (serverId) => 'Failed to fetch hubs from server $serverId',
      fetch: (serverId, client) async {
        final serverLibraries = libraries?[serverId];
        final shouldUseGlobalHubs = useGlobalHubs && client.capabilities.richHubs;
        final hubItemLimit = limit ?? defaultHubPreviewLimit;
        final hubs = shouldUseGlobalHubs
            ? [
                ...await client.fetchGlobalHubs(limit: hubItemLimit, includePlaybackHubs: includePlaybackHubs),
                // Plex's promoted/global hub endpoint never includes music
                // libraries — append their per-library hubs so music rows
                // reach home. No-op (zero extra calls) without a visible
                // music library.
                ...await _fetchLibraryHubsForClient(
                  client,
                  limit: hubItemLimit,
                  hiddenLibraryKeys: hiddenLibraryKeys,
                  includePlaybackHubs: includePlaybackHubs,
                  libraries: serverLibraries ?? const [],
                  kinds: const {MediaKind.artist},
                ),
              ]
            : await _fetchLibraryHubsForClient(
                client,
                limit: hubItemLimit,
                hiddenLibraryKeys: hiddenLibraryKeys,
                includePlaybackHubs: includePlaybackHubs,
                libraries: useGlobalHubs ? serverLibraries : null,
              );
        return _postProcessHubs(hubs, serverId: ServerId(serverId), hiddenLibraryKeys: hiddenLibraryKeys);
      },
    );

    final all = fetched.items;
    final hubs = limit != null && limit < all.length ? all.sublist(0, limit) : all;
    return (hubs: hubs, succeededServerIds: fetched.succeededServerIds, cancelledServerIds: fetched.cancelledServerIds);
  }

  /// Per-library hub fetch for a single client. Filters to visible libraries
  /// of [kinds] (movie/show/clip/artist by default — clip covers Jellyfin
  /// musicvideos/homevideos, #1476; artist brings music rows to home) and
  /// concatenates the results. The rich-hub music append passes
  /// `{MediaKind.artist}` to fetch only what the global endpoint misses.
  Future<List<MediaHub>> _fetchLibraryHubsForClient(
    MediaServerClient client, {
    required int limit,
    Set<String>? hiddenLibraryKeys,
    required bool includePlaybackHubs,
    List<MediaLibrary>? libraries,
    Set<MediaKind> kinds = const {MediaKind.movie, MediaKind.show, MediaKind.clip, MediaKind.artist},
  }) async {
    final libs = libraries ?? await client.fetchLibraries();
    final visible = libs.where((l) {
      if (!kinds.contains(l.kind)) return false;
      if (l.hidden) return false;
      if (hiddenLibraryKeys != null && hiddenLibraryKeys.contains(l.globalKey)) return false;
      return true;
    }).toList();

    const concurrency = 3;
    final all = <MediaHub>[];
    for (var start = 0; start < visible.length; start += concurrency) {
      final batch = visible.skip(start).take(concurrency);
      final results = await Future.wait(
        batch.map((l) async {
          try {
            return await client.fetchLibraryHubs(
              l.id,
              libraryName: l.title,
              limit: limit,
              includePlaybackHubs: includePlaybackHubs,
              libraryKind: l.kind,
            );
          } catch (e, st) {
            appLogger.e('Failed to fetch library hubs for ${l.globalKey}', error: e, stackTrace: st);
            return <MediaHub>[];
          }
        }),
      );
      for (final list in results) {
        all.addAll(list);
      }
    }
    return all;
  }

  /// Filter hidden-library items and drop empty hubs.
  List<MediaHub> _postProcessHubs(List<MediaHub> hubs, {required ServerId serverId, Set<String>? hiddenLibraryKeys}) {
    var filtered = hubs;
    if (hiddenLibraryKeys != null && hiddenLibraryKeys.isNotEmpty) {
      filtered = filtered
          .map((hub) {
            final filteredItems = hub.items.where((item) {
              final libraryId = item.libraryId;
              if (libraryId == null) return true;
              final globalKey = buildGlobalKey(ServerId(serverId), libraryId);
              return !hiddenLibraryKeys.contains(globalKey);
            }).toList();
            if (filteredItems.isEmpty) return null;
            return hub.copyWith(items: filteredItems, size: filteredItems.length);
          })
          .whereType<MediaHub>()
          .toList();
    }
    return filtered;
  }

  /// Search across all online servers (Plex + Jellyfin). Returns neutral
  /// [MediaItem]s.
  Future<List<MediaItem>> searchAcrossServers(String query, {int? limit}) async {
    if (query.trim().isEmpty) {
      return [];
    }

    final clients = _serverManager.onlineClients;
    if (clients.isEmpty) return [];

    final resultLimit = limit ?? defaultMediaSearchLimit;
    final fetchLimit = resultLimit < defaultMediaSearchLimit ? defaultMediaSearchLimit : resultLimit;

    final fetched = await _fanOut<MediaItem>(
      clients,
      failureMessage: (serverId) => 'Search failed on $serverId',
      fetch: (_, client) => client.searchItems(query, limit: fetchLimit),
    );
    final result = rankMediaSearchResults(fetched.items, query, limit: resultLimit);

    appLogger.i('Found ${result.length} search results across all servers');

    return result;
  }

  /// Reverse external-id lookup fanned out to every online server (see
  /// [MediaServerClient.findByExternalIds]). One request wave per tap on an
  /// Explore catalog item; per-server failures are logged and skipped.
  Future<List<MediaItem>> findByExternalIdsAcrossServers(
    ExternalIds ids, {
    required MediaKind kind,
    String? title,
    int? year,
  }) async {
    if (!ids.hasAny) return [];
    final clients = _serverManager.onlineClients;
    if (clients.isEmpty) return [];

    final futures = clients.entries.map((entry) async {
      try {
        return await entry.value.findByExternalIds(ids, kind: kind, title: title, year: year);
      } catch (e, st) {
        appLogger.w('External-id lookup failed on ${entry.key}', error: e, stackTrace: st);
        return null;
      }
    });

    return (await Future.wait(futures)).nonNulls.toList();
  }

  /// Group libraries by server (internal aggregation helper).
  Map<String, List<MediaLibrary>> _groupLibrariesByServer(List<MediaLibrary> libraries) {
    final grouped = <String, List<MediaLibrary>>{};

    for (final library in libraries) {
      final serverId = library.serverId;
      if (serverId != null) {
        grouped.putIfAbsent(serverId, () => []).add(library);
      }
    }

    return grouped;
  }
}