import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:go_router/go_router.dart';
import 'package:worldhopper/l10n/app_localizations.dart';
import 'package:worldhopper/config/constants.dart';
import 'package:worldhopper/helpers/responsive_helper.dart';
import 'package:worldhopper/helpers/snackbar_helper.dart';
import 'package:worldhopper/models/downloaded_series.dart';
import 'package:worldhopper/models/feed.dart';
import 'package:worldhopper/models/entry.dart';
import 'package:worldhopper/providers/feed_provider.dart';
import 'package:worldhopper/providers/server_provider.dart';
import 'package:worldhopper/providers/connectivity_provider.dart';
import 'package:worldhopper/services/url_helper.dart';
import 'package:worldhopper/providers/download_provider.dart';
import 'package:worldhopper/services/series_download_service.dart';
import 'package:worldhopper/widgets/download_badge.dart';
import 'package:worldhopper/widgets/publication_card.dart';
import 'package:worldhopper/widgets/worldhopper_app_bar.dart';

/// Generic screen for displaying any OPDS feed
class FeedScreen extends ConsumerStatefulWidget {
  final String serverId;
  final String feedUrl;
  final String feedTitle;

  const FeedScreen({
    super.key,
    required this.serverId,
    required this.feedUrl,
    required this.feedTitle,
  });

  @override
  ConsumerState<FeedScreen> createState() => _FeedScreenState();
}

class _FeedScreenState extends ConsumerState<FeedScreen> {
  List<Entry> _allEntries = [];
  String? _nextPageUrl;
  bool _isLoadingMore = false;
  bool _initialized = false;
  bool _isAcquisitionFeed = false;
  final ScrollController _scrollController = ScrollController();

  @override
  void initState() {
    super.initState();
    _scrollController.addListener(_onScroll);
  }

  @override
  void dispose() {
    _scrollController.dispose();
    super.dispose();
  }

  void _onScroll() {
    if (_isLoadingMore || _nextPageUrl == null) return;

    // Load more when user scrolls to 80% of the content
    final maxScroll = _scrollController.position.maxScrollExtent;
    final currentScroll = _scrollController.position.pixels;
    final threshold = maxScroll * 0.8;

    if (currentScroll >= threshold) {
      _loadMoreEntries();
    }
  }

  @override
  Widget build(BuildContext context) {
    final feedRequest = FeedRequest(
      serverId: widget.serverId,
      url: widget.feedUrl,
      forceRefresh: false,
    );
    final feedAsync = ref.watch(feedProvider(feedRequest));

    // Watch download status for this feed
    final downloadStatusAsync = ref.watch(seriesDownloadStatusProvider(
      SeriesDownloadKey(serverId: widget.serverId, feedUrl: widget.feedUrl),
    ));

    // Listen to download progress for completion/error feedback
    ref.listen<AsyncValue<DownloadProgress>>(activeDownloadProgressProvider,
        (previous, next) {
      next.whenData((progress) {
        if (progress.status == DownloadStatus.complete ||
            progress.status == DownloadStatus.partial ||
            progress.status == DownloadStatus.failed) {
          if (!mounted) return;
          final l10n = AppLocalizations.of(context);
          switch (progress.status) {
            case DownloadStatus.complete:
              context.showInfoSnackBar(
                '${l10n.downloadComplete}: ${progress.seriesTitle}',
              );
            case DownloadStatus.partial:
              context.showErrorSnackBar(
                '${l10n.downloadFailed}: ${progress.seriesTitle} '
                '(${progress.completedChapters}/${progress.totalChapters})',
              );
            case DownloadStatus.failed:
              context.showErrorSnackBar(
                '${l10n.downloadFailed}: ${progress.seriesTitle}',
              );
            default:
              break;
          }
        }
      });
    });

    return Scaffold(
      appBar: WorldhopperAppBar(
        title: Text(widget.feedTitle),
        actions: _isAcquisitionFeed
            ? [_buildDownloadAction(context, ref, downloadStatusAsync)]
            : null,
      ),
      body: feedAsync.when(
        data: (feed) => _buildFeedContent(context, ref, feed),
        loading: () => const Center(child: CircularProgressIndicator()),
        error: (error, stack) => _buildErrorState(context, ref, error),
      ),
    );
  }

  Widget _buildFeedContent(BuildContext context, WidgetRef ref, Feed feed) {
    final l10n = AppLocalizations.of(context);

    // Initialize entries only once when first loaded
    if (!_initialized) {
      WidgetsBinding.instance.addPostFrameCallback((_) {
        if (mounted && !_initialized) {
          setState(() {
            _allEntries = List.from(feed.entries);
            _nextPageUrl = feed.nextLink?.href;
            _isAcquisitionFeed = feed.isAcquisitionFeed;
            _initialized = true;
          });
        }
      });
    }

    return RefreshIndicator(
      onRefresh: () async {
        // Clear the repository cache for this specific feed
        final repository = ref.read(feedRepositoryProvider);
        final server = await ref.read(serverProvider(widget.serverId).future);
        if (server != null) {
          final resolvedUrl = UrlHelper.resolveUrl(server.url, widget.feedUrl);
          repository.clearFeedCache(widget.serverId, resolvedUrl);
        }
        // Reset pagination state
        setState(() {
          _allEntries = [];
          _nextPageUrl = null;
          _initialized = false;
        });
        // Invalidate the provider to force refetch
        final refreshRequest = FeedRequest(
          serverId: widget.serverId,
          url: widget.feedUrl,
          forceRefresh: false,
        );
        ref.invalidate(feedProvider(refreshRequest));
        // Wait for the new data to load
        await ref.read(feedProvider(refreshRequest).future);
      },
      child: _allEntries.isEmpty
          ? _buildEmptyState(context, l10n)
          : LayoutBuilder(
              builder: (context, constraints) {
                return SingleChildScrollView(
                  physics: const AlwaysScrollableScrollPhysics(),
                  controller: _scrollController,
                  child: ConstrainedBox(
                    constraints: BoxConstraints(
                      minHeight: constraints.maxHeight,
                    ),
                    child: GridView.builder(
                      shrinkWrap: true,
                      physics: const NeverScrollableScrollPhysics(),
                      padding: const EdgeInsets.all(16),
                      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                        crossAxisCount: gridColumnCount(constraints.maxWidth),
                        childAspectRatio: 0.65,
                        crossAxisSpacing: 12,
                        mainAxisSpacing: 12,
                      ),
                      itemCount: _allEntries.length + (_isLoadingMore ? 1 : 0),
                      itemBuilder: (context, index) {
                        // Show loading indicator at the end
                        if (index == _allEntries.length) {
                          return Center(
                            child: Padding(
                              padding: const EdgeInsets.all(16),
                              child: CircularProgressIndicator(
                                color: Theme.of(context).colorScheme.primary,
                              ),
                            ),
                          );
                        }

                        final entry = _allEntries[index];
                        return PublicationCard(
                          entry: entry,
                          serverId: widget.serverId,
                          badge: _isAcquisitionFeed && !entry.isNavigation
                              ? DownloadBadge(
                                  serverId: widget.serverId,
                                  entryId: entry.id,
                                )
                              : null,
                          onTap: () async {
                            if (entry.isNavigation) {
                              // Navigate to nested feed
                              final subsectionLink = entry.links.firstWhere(
                                (link) =>
                                    link.rel == 'subsection' ||
                                    link.rel.contains('navigation') ||
                                    link.rel == 'self',
                                orElse: () => entry.links.first,
                              );

                              context.push(
                                '/browse/${widget.serverId}/feed',
                                extra: {
                                  'feedUrl': subsectionLink.href,
                                  'feedTitle': entry.title,
                                },
                              );
                            } else {
                              // Check connectivity before navigating to publication detail
                              final connectivityState =
                                  ref.read(connectivityStateProvider);
                              final isOnline = connectivityState.whenOrNull(
                                    data: (online) => online,
                                  ) ??
                                  true;

                              // If offline, check content availability and show warning
                              if (!isOnline) {
                                final checker =
                                    ref.read(offlineContentCheckerProvider);
                                final isAvailable = await checker
                                    .isContentAvailableOffline(entry);

                                if (!isAvailable) {
                                  if (entry.isEpub) {
                                    // Warn for uncached EPUBs
                                    if (!context.mounted) return;
                                    context.showInfoSnackBar(
                                      l10n.browserOfflineEpubNotCached,
                                      duration: const Duration(seconds: 3),
                                    );
                                  } else if (entry.hasStreamLink) {
                                    // Warn for OPDS-PS streams
                                    if (!context.mounted) return;
                                    context.showInfoSnackBar(
                                      l10n.browserOfflinePagesWarning,
                                      duration: const Duration(seconds: 3),
                                    );
                                  }
                                }
                              }

                              // Navigate to publication detail
                              if (!context.mounted) return;
                              context.push(
                                AppConstants.routePublicationDetail,
                                extra: {
                                  'entry': entry,
                                  'serverId': widget.serverId,
                                  'feedUrl': widget.feedUrl,
                                },
                              );
                            }
                          },
                        );
                      },
                    ),
                  ),
                );
              },
            ),
    );
  }

  Future<void> _loadMoreEntries() async {
    if (_isLoadingMore || _nextPageUrl == null) return;

    setState(() {
      _isLoadingMore = true;
    });

    try {
      final repository = ref.read(feedRepositoryProvider);
      final nextFeed = await repository.fetchFeed(
        widget.serverId,
        _nextPageUrl!,
      );

      setState(() {
        _allEntries.addAll(nextFeed.entries);
        _nextPageUrl = nextFeed.nextLink?.href;
        _isLoadingMore = false;
      });
    } catch (e) {
      setState(() {
        _isLoadingMore = false;
      });

      if (mounted) {
        final l10n = AppLocalizations.of(context);
        context.showErrorSnackBar(l10n.browserFailedToLoadMore(e.toString()));
      }
    }
  }

  Widget _buildEmptyState(BuildContext context, AppLocalizations l10n) {
    return LayoutBuilder(
      builder: (context, constraints) {
        return SingleChildScrollView(
          physics: const AlwaysScrollableScrollPhysics(),
          child: ConstrainedBox(
            constraints: BoxConstraints(
              minHeight: constraints.maxHeight,
            ),
            child: Center(
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  Icon(
                    Icons.folder_open,
                    size: 80,
                    color: Theme.of(context)
                        .colorScheme
                        .secondary
                        .withValues(alpha: 0.5),
                  ),
                  const SizedBox(height: 24),
                  Text(
                    l10n.browserNoContent,
                    style: Theme.of(context).textTheme.headlineSmall,
                  ),
                  const SizedBox(height: 8),
                  Text(
                    l10n.browserCollectionEmpty,
                    style: Theme.of(context).textTheme.bodyMedium?.copyWith(
                          color: Theme.of(context)
                              .colorScheme
                              .onSurface
                              .withValues(alpha: 0.7),
                        ),
                  ),
                ],
              ),
            ),
          ),
        );
      },
    );
  }

  Widget _buildDownloadAction(
    BuildContext context,
    WidgetRef ref,
    AsyncValue<DownloadedSeries?> downloadStatusAsync,
  ) {
    final l10n = AppLocalizations.of(context);

    return downloadStatusAsync.when(
      data: (series) {
        if (series == null) {
          // Not downloaded - show download button
          return IconButton(
            icon: const Icon(Icons.download),
            tooltip: l10n.downloadAll,
            onPressed: () => _confirmAndStartDownload(context, ref),
          );
        }
        if (series.isDownloading) {
          // Downloading - show progress with cancel
          return IconButton(
            icon: SizedBox(
              width: 24,
              height: 24,
              child: CircularProgressIndicator(
                value: series.progress > 0 ? series.progress : null,
                strokeWidth: 2,
              ),
            ),
            tooltip: l10n.downloadCancel,
            onPressed: () {
              ref
                  .read(downloadNotifierProvider.notifier)
                  .cancelDownload(series.id);
            },
          );
        }
        // Terminal state — differentiate complete vs partial/failed
        final (IconData icon, Color color) = switch (series.status) {
          DownloadStatus.complete => (Icons.download_done, Colors.green),
          DownloadStatus.failed => (Icons.error_outline, Colors.red),
          _ => (Icons.download_done, Colors.orange),
        };
        return IconButton(
          icon: Icon(icon, color: color),
          tooltip: l10n.downloadDelete,
          onPressed: () => _confirmDeleteDownload(context, ref, series),
        );
      },
      loading: () => const SizedBox(
        width: 48,
        child: Center(
          child: SizedBox(
            width: 20,
            height: 20,
            child: CircularProgressIndicator(strokeWidth: 2),
          ),
        ),
      ),
      error: (_, __) => IconButton(
        icon: const Icon(Icons.download),
        tooltip: l10n.downloadAll,
        onPressed: () => _confirmAndStartDownload(context, ref),
      ),
    );
  }

  Future<void> _confirmAndStartDownload(
      BuildContext context, WidgetRef ref) async {
    final l10n = AppLocalizations.of(context);

    // Count downloadable entries
    final downloadableCount =
        _allEntries.where((e) => e.isEpub || e.isImageStream).length;

    if (downloadableCount == 0) return;

    final confirmed = await showDialog<bool>(
      context: context,
      builder: (context) => AlertDialog(
        title: Text(l10n.downloadConfirmTitle),
        content: Text(l10n.downloadConfirmMessage(downloadableCount)),
        actions: [
          TextButton(
            onPressed: () => Navigator.of(context).pop(false),
            child: Text(l10n.commonCancel),
          ),
          FilledButton(
            onPressed: () => Navigator.of(context).pop(true),
            child: Text(l10n.downloadConfirmStart),
          ),
        ],
      ),
    );

    if (confirmed != true || !context.mounted) return;

    // Get the server
    final server = await ref.read(serverProvider(widget.serverId).future);
    if (server == null) return;

    // Get the current feed for pagination info
    final feedRequest = FeedRequest(
      serverId: widget.serverId,
      url: widget.feedUrl,
      forceRefresh: false,
    );
    final feed = await ref.read(feedProvider(feedRequest).future);

    // Get a cover URL from the first entry with a cover
    final coverEntry = _allEntries.firstWhere(
      (e) => e.thumbnailUrl != null || e.coverUrl != null,
      orElse: () => _allEntries.first,
    );

    if (!context.mounted) return;
    context.showInfoSnackBar(l10n.downloadStarting);

    ref.read(downloadNotifierProvider.notifier).startSeriesDownload(
          server: server,
          feedUrl: widget.feedUrl,
          feedTitle: widget.feedTitle,
          initialFeed: feed,
          coverUrl: coverEntry.coverUrl,
          thumbnailUrl: coverEntry.thumbnailUrl,
        );

    // Invalidate download status to update UI
    ref.invalidate(seriesDownloadStatusProvider(
      SeriesDownloadKey(serverId: widget.serverId, feedUrl: widget.feedUrl),
    ));
  }

  Future<void> _confirmDeleteDownload(
    BuildContext context,
    WidgetRef ref,
    DownloadedSeries series,
  ) async {
    final l10n = AppLocalizations.of(context);

    final confirmed = await showDialog<bool>(
      context: context,
      builder: (context) => AlertDialog(
        title: Text(l10n.downloadDeleteSeries),
        content: Text(l10n.downloadDeleteSeriesConfirmation(series.title)),
        actions: [
          TextButton(
            onPressed: () => Navigator.of(context).pop(false),
            child: Text(l10n.commonCancel),
          ),
          FilledButton(
            onPressed: () => Navigator.of(context).pop(true),
            style: FilledButton.styleFrom(
              backgroundColor: Theme.of(context).colorScheme.error,
            ),
            child: Text(l10n.commonDelete),
          ),
        ],
      ),
    );

    if (confirmed == true) {
      await ref.read(downloadNotifierProvider.notifier).deleteSeries(series.id);
      if (context.mounted) {
        ref.invalidate(seriesDownloadStatusProvider(
          SeriesDownloadKey(serverId: widget.serverId, feedUrl: widget.feedUrl),
        ));
      }
    }
  }

  Widget _buildErrorState(BuildContext context, WidgetRef ref, Object error) {
    final l10n = AppLocalizations.of(context);

    return Center(
      child: Padding(
        padding: const EdgeInsets.all(32),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Icon(Icons.error_outline, size: 64, color: Colors.red),
            const SizedBox(height: 24),
            Text(
              l10n.browserFailedToLoadFeed,
              style: Theme.of(context).textTheme.titleLarge,
              textAlign: TextAlign.center,
            ),
            const SizedBox(height: 12),
            Text(
              error.toString(),
              style: Theme.of(context).textTheme.bodyMedium,
              textAlign: TextAlign.center,
            ),
            const SizedBox(height: 24),
            ElevatedButton.icon(
              onPressed: () {
                final refreshRequest = FeedRequest(
                  serverId: widget.serverId,
                  url: widget.feedUrl,
                  forceRefresh: false,
                );
                ref.invalidate(feedProvider(refreshRequest));
              },
              icon: const Icon(Icons.refresh),
              label: Text(l10n.browserRetry),
            ),
          ],
        ),
      ),
    );
  }
}