import 'package:dio/dio.dart';
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:go_router/go_router.dart';

import '../api/errors.dart';
import '../models/album.dart';
import '../models/artist.dart';
import '../models/playlist.dart';
import '../models/system_playlists_status.dart';
import '../models/track.dart';
import '../playlists/playlists_provider.dart';
import '../playlists/widgets/playlist_card.dart';
import '../playlists/widgets/playlist_placeholder_card.dart';
import '../shared/delayed_loading.dart';
import '../shared/widgets/connection_error_banner.dart';
import '../shared/widgets/main_app_bar_actions.dart';
import '../theme/theme_extension.dart';
import 'library_providers.dart';
import 'widgets/album_card.dart';
import 'widgets/artist_card.dart';
import 'widgets/compact_track_card.dart';
import 'widgets/horizontal_scroll_row.dart';

class HomeScreen extends ConsumerWidget {
  const HomeScreen({super.key});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final fs = Theme.of(context).extension<FabledSwordTheme>()!;
    final home = ref.watch(homeProvider);
    final allPlaylists = ref.watch(playlistsListProvider('all'));
    final status = ref.watch(systemPlaylistsStatusProvider);
    return Scaffold(
      backgroundColor: fs.obsidian,
      appBar: AppBar(
        backgroundColor: fs.obsidian,
        elevation: 0,
        title: Text('Minstrel', style: TextStyle(color: fs.parchment)),
        actions: const [MainAppBarActions(currentRoute: '/home')],
      ),
      body: SafeArea(
        child: home.when(
          error: (e, _) {
            final code = e is DioException ? ApiError.fromDio(e).code : 'unknown';
            if (code == 'connection_refused') {
              return ConnectionErrorBanner(
                onRetry: () => ref.refresh(homeProvider),
              );
            }
            return Center(child: Text('$e', style: TextStyle(color: fs.error)));
          },
          loading: () => const DelayedLoading(
            isLoading: true,
            whenReady: SizedBox.shrink(),
            whileDelayed:
                Center(child: CircularProgressIndicator()),
          ),
          data: (h) => RefreshIndicator(
            onRefresh: () async => ref.refresh(homeProvider.future),
            child: ListView(children: [
              _PlaylistsSection(
                playlists: allPlaylists.value?.owned ?? const [],
                status: status.value ?? SystemPlaylistsStatus.empty(),
              ),
              _RecentlyAddedSection(albums: h.recentlyAddedAlbums),
              _RediscoverSection(
                albums: h.rediscoverAlbums,
                artists: h.rediscoverArtists,
              ),
              _MostPlayedSection(tracks: h.mostPlayedTracks),
              _LastPlayedSection(artists: h.lastPlayedArtists),
              const SizedBox(height: 96),
            ]),
          ),
        ),
      ),
    );
  }
}

class _PlaylistsSection extends StatelessWidget {
  const _PlaylistsSection({required this.playlists, required this.status});
  final List<Playlist> playlists;
  final SystemPlaylistsStatus status;

  @override
  Widget build(BuildContext context) {
    final items = _buildPlaylistsRow(playlists, status);
    return HorizontalScrollRow(
      title: 'Playlists',
      height: 220,
      children: items.map((item) {
        if (item is _RealPlaylist) {
          return PlaylistCard(playlist: item.playlist);
        }
        final ph = item as _PlaceholderPlaylist;
        return PlaylistPlaceholderCard(label: ph.label, variant: ph.variant);
      }).toList(),
    );
  }
}

abstract class _PlaylistRowItem {}
class _RealPlaylist extends _PlaylistRowItem {
  _RealPlaylist(this.playlist);
  final Playlist playlist;
}
class _PlaceholderPlaylist extends _PlaylistRowItem {
  _PlaceholderPlaylist(this.label, this.variant);
  final String label;
  final String variant;
}

List<_PlaylistRowItem> _buildPlaylistsRow(
  List<Playlist> ownedAll,
  SystemPlaylistsStatus status,
) {
  final out = <_PlaylistRowItem>[];

  Playlist? findFirst(bool Function(Playlist) test) {
    for (final p in ownedAll) {
      if (test(p)) return p;
    }
    return null;
  }

  // Slot 1: For-You.
  final forYou = findFirst((p) => p.systemVariant == 'for_you');
  out.add(forYou != null
      ? _RealPlaylist(forYou)
      : _PlaceholderPlaylist('For You', _variantFor('for-you', status)));

  // Slots 2-4: Songs-like (real first, padded to 3).
  final songsLike = ownedAll
      .where((p) => p.systemVariant == 'songs_like_artist')
      .take(3)
      .toList();
  for (var i = 0; i < 3; i++) {
    out.add(i < songsLike.length
        ? _RealPlaylist(songsLike[i])
        : _PlaceholderPlaylist('Songs like…', _variantFor('songs-like', status)));
  }

  // User-created trail (server returns most-recently-updated first).
  for (final p in ownedAll.where((p) => p.systemVariant == null)) {
    out.add(_RealPlaylist(p));
  }

  return out;
}

String _variantFor(String slot, SystemPlaylistsStatus s) {
  if (s.inFlight) return 'building';
  if (s.lastError != null) return 'failed';
  if (slot == 'songs-like' && s.lastRunAt != null) return 'seed-needed';
  return 'pending';
}

class _RecentlyAddedSection extends StatelessWidget {
  const _RecentlyAddedSection({required this.albums});
  final List<AlbumRef> albums;

  @override
  Widget build(BuildContext context) {
    if (albums.isEmpty) {
      return const _EmptySection(
        title: 'Recently added',
        message: "Nothing added yet. Scan a folder via the server's config.",
      );
    }
    final controller = ScrollController();
    final rows = _chunk(albums, 25);
    return Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
      for (var i = 0; i < rows.length; i++)
        HorizontalScrollRow(
          title: i == 0 ? 'Recently added' : '',
          controller: controller,
          children: rows[i]
              .map((a) => AlbumCard(
                    album: a,
                    onTap: () =>
                        _push(context, '/albums/${a.id}'),
                  ))
              .toList(),
        ),
    ]);
  }
}

class _RediscoverSection extends StatelessWidget {
  const _RediscoverSection({required this.albums, required this.artists});
  final List<AlbumRef> albums;
  final List<ArtistRef> artists;

  @override
  Widget build(BuildContext context) {
    if (albums.isEmpty && artists.isEmpty) {
      return const _EmptySection(
        title: 'Rediscover',
        message:
            'No forgotten favourites yet. Like some albums or artists to fill this in.',
      );
    }
    return Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
      if (albums.isNotEmpty)
        HorizontalScrollRow(
          title: 'Rediscover',
          children: albums
              .map((a) => AlbumCard(
                    album: a,
                    onTap: () =>
                        _push(context, '/albums/${a.id}'),
                  ))
              .toList(),
        ),
      if (artists.isNotEmpty)
        HorizontalScrollRow(
          title: albums.isEmpty ? 'Rediscover' : '',
          height: 168,
          children: artists
              .map((ar) => ArtistCard(
                    artist: ar,
                    onTap: () =>
                        _push(context, '/artists/${ar.id}'),
                  ))
              .toList(),
        ),
    ]);
  }
}

class _MostPlayedSection extends StatelessWidget {
  const _MostPlayedSection({required this.tracks});
  final List<TrackRef> tracks;

  @override
  Widget build(BuildContext context) {
    if (tracks.isEmpty) {
      return const _EmptySection(
        title: 'Most played',
        message: 'No plays to draw from. Listen to something.',
      );
    }
    final controller = ScrollController();
    final rows = _chunk(tracks, 25);
    return Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
      for (var i = 0; i < rows.length; i++)
        HorizontalScrollRow(
          title: i == 0 ? 'Most played' : '',
          height: 64,
          controller: controller,
          children: [
            for (var j = 0; j < rows[i].length; j++)
              CompactTrackCard(
                track: rows[i][j],
                sectionTracks: tracks,
                index: i * 25 + j,
              ),
          ],
        ),
    ]);
  }
}

class _LastPlayedSection extends StatelessWidget {
  const _LastPlayedSection({required this.artists});
  final List<ArtistRef> artists;

  @override
  Widget build(BuildContext context) {
    if (artists.isEmpty) {
      return const _EmptySection(
        title: 'Last played',
        message: 'No recent plays.',
      );
    }
    return HorizontalScrollRow(
      title: 'Last played',
      height: 168,
      children: artists
          .map((ar) => ArtistCard(
                artist: ar,
                onTap: () => _push(context, '/artists/${ar.id}'),
              ))
          .toList(),
    );
  }
}

class _EmptySection extends StatelessWidget {
  const _EmptySection({required this.title, required this.message});
  final String title;
  final String message;

  @override
  Widget build(BuildContext context) {
    final fs = Theme.of(context).extension<FabledSwordTheme>()!;
    return Padding(
      padding: const EdgeInsets.fromLTRB(16, 8, 16, 16),
      child: Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
        Text(
          title,
          style: TextStyle(
            fontFamily: fs.display.fontFamily,
            fontSize: 18,
            color: fs.parchment,
          ),
        ),
        const SizedBox(height: 8),
        Text(message, style: TextStyle(color: fs.ash)),
      ]),
    );
  }
}

void _push(BuildContext context, String path) {
  context.push(path);
}

List<List<T>> _chunk<T>(List<T> items, int size) {
  final out = <List<T>>[];
  for (var i = 0; i < items.length; i += size) {
    out.add(items.sublist(i, i + size > items.length ? items.length : i + size));
  }
  return out;
}