import 'dart:async';
import 'dart:io';

import 'package:flutter/material.dart';
import 'package:photo_view/photo_view.dart';

import '../../routing/app_routes.dart';
import '../app_progress_indicator.dart';
import '../file_viewer/local_file_actions.dart';
import '../info_dialog.dart';
import 'gallery_cache.dart';
import 'gallery_image_page.dart';
import 'gallery_item.dart';
import 'gallery_source.dart';
import 'gallery_video_page.dart';

enum _GalleryAction { openExternal, sendToChat, saveToCloud, share, save }

/// Full-screen, swipeable view over the images and videos of a chat or
/// folder. Owns (and disposes) [source].
class MediaGalleryViewer extends StatefulWidget {
  final GallerySource source;
  final String initialKey;

  const MediaGalleryViewer({
    required this.source,
    required this.initialKey,
    super.key,
  });

  @override
  State<MediaGalleryViewer> createState() => _MediaGalleryViewerState();
}

class _MediaGalleryViewerState extends State<MediaGalleryViewer> {
  /// Neighbours whose previews are fetched ahead, per side.
  static const _precacheRange = 2;

  late final PageController _pageController;
  final ValueNotifier<int> _rotateSignal = ValueNotifier(0);
  late String _anchorKey;
  late int _index;
  bool _busy = false;

  List<GalleryItem> get _items => widget.source.items;

  GalleryItem get _current => _items[_index];

  @override
  void initState() {
    super.initState();
    _anchorKey = widget.initialKey;
    _index = _items.indexWhere((item) => item.key == _anchorKey);
    if (_index < 0) _index = 0;
    _pageController = PageController(initialPage: _index);
    widget.source.addListener(_onSourceChanged);
    WidgetsBinding.instance.addPostFrameCallback((_) {
      if (mounted) _onIndexSettled();
    });
  }

  @override
  void dispose() {
    widget.source.removeListener(_onSourceChanged);
    widget.source.dispose();
    _pageController.dispose();
    _rotateSignal.dispose();
    super.dispose();
  }

  /// Older chat media lands in front of the shown item; jump along so the
  /// user keeps looking at the same picture.
  void _onSourceChanged() {
    if (!mounted) return;
    final index = _items.indexWhere((item) => item.key == _anchorKey);
    setState(() {
      if (index >= 0) _index = index;
    });
    if (index >= 0 &&
        _pageController.hasClients &&
        _pageController.page?.round() != index) {
      _pageController.jumpToPage(index);
    }
    _precacheAround();
  }

  void _onPageChanged(int index) {
    setState(() {
      _index = index;
      _anchorKey = _items[index].key;
    });
    _onIndexSettled();
  }

  void _onIndexSettled() {
    _precacheAround();
    if (_index <= _precacheRange && widget.source.hasOlder) {
      unawaited(widget.source.loadOlder());
    }
  }

  void _precacheAround() {
    for (var d = -_precacheRange; d <= _precacheRange; d++) {
      final i = _index + d;
      if (d == 0 || i < 0 || i >= _items.length) continue;
      unawaited(
        precacheImage(
          galleryPreviewProvider(context, _items[i]),
          context,
          onError: (_, _) {},
        ),
      );
    }
  }

  Future<void> _handleAction(_GalleryAction action) async {
    final item = _current;
    switch (action) {
      case _GalleryAction.sendToChat:
        AppRoutes.openInternalShareToChat(context, item.file);
        return;
      case _GalleryAction.saveToCloud:
        AppRoutes.openInternalSaveToFolder(context, item.file);
        return;
      case _GalleryAction.openExternal:
      case _GalleryAction.share:
      case _GalleryAction.save:
        break;
    }
    if (_busy) return;
    setState(() => _busy = true);
    final String path;
    try {
      path = await GalleryOriginals.instance.namedCopy(item);
    } on Object catch (e) {
      if (mounted) InfoDialog.showError(context, e);
      return;
    } finally {
      if (mounted) setState(() => _busy = false);
    }
    if (!mounted) return;
    switch (action) {
      case _GalleryAction.openExternal:
        AppRoutes.openFileViewer(
          context,
          path,
          openExternal: true,
          remoteFile: item.file,
        );
      case _GalleryAction.share:
        await shareLocalFile(context, path);
      case _GalleryAction.save:
        await saveLocalFile(context, path);
      case _GalleryAction.sendToChat:
      case _GalleryAction.saveToCloud:
        break;
    }
  }

  PreferredSizeWidget _appBar(BuildContext context) {
    final item = _current;
    final subtitle = item.subtitle;
    final position = '${_index + 1} / ${_items.length}';
    return AppBar(
      title: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        mainAxisSize: MainAxisSize.min,
        children: [
          Text(item.file.name, maxLines: 1, overflow: TextOverflow.ellipsis),
          Text(
            subtitle == null ? position : '$position · $subtitle',
            maxLines: 1,
            overflow: TextOverflow.ellipsis,
            style: Theme.of(context).textTheme.bodySmall,
          ),
        ],
      ),
      actions: [
        if (_busy)
          const Padding(
            padding: EdgeInsets.symmetric(horizontal: 12),
            child: Center(child: AppProgressIndicator.small()),
          ),
        if (!item.isVideo)
          IconButton(
            onPressed: () => _rotateSignal.value++,
            tooltip: 'Drehen',
            icon: const Icon(Icons.rotate_right),
          ),
        PopupMenuButton<_GalleryAction>(
          tooltip: 'Dateiaktionen',
          onSelected: (action) => unawaited(_handleAction(action)),
          itemBuilder: (context) => [
            _menuItem(
              _GalleryAction.openExternal,
              Platform.isIOS ? Icons.ios_share : Icons.open_in_new,
              Platform.isIOS ? 'Extern öffnen' : 'Öffnen mit',
            ),
            _menuItem(
              _GalleryAction.sendToChat,
              Icons.chat_bubble_outline,
              'An Talk-Chat senden',
            ),
            _menuItem(
              _GalleryAction.saveToCloud,
              Icons.cloud_outlined,
              'In Cloud speichern',
            ),
            _menuItem(_GalleryAction.share, Icons.share_outlined, 'Teilen'),
            _menuItem(
              _GalleryAction.save,
              Icons.save_alt_outlined,
              'Speichern',
            ),
          ],
        ),
      ],
    );
  }

  PopupMenuItem<_GalleryAction> _menuItem(
    _GalleryAction action,
    IconData icon,
    String label,
  ) => PopupMenuItem(
    value: action,
    child: ListTile(leading: Icon(icon), title: Text(label), dense: true),
  );

  int? _indexForKey(Key key) {
    if (key is! ValueKey<String>) return null;
    final index = _items.indexWhere((item) => item.key == key.value);
    return index < 0 ? null : index;
  }

  @override
  Widget build(BuildContext context) => Scaffold(
    appBar: _appBar(context),
    backgroundColor: Theme.of(context).colorScheme.surface,
    // The scope lets a page's PhotoView hand horizontal drags to the
    // PageView once the image is panned to its edge.
    body: PhotoViewGestureDetectorScope(
      axis: Axis.horizontal,
      child: PageView.builder(
        controller: _pageController,
        itemCount: _items.length,
        onPageChanged: _onPageChanged,
        allowImplicitScrolling: true,
        findChildIndexCallback: _indexForKey,
        itemBuilder: (context, index) {
          final item = _items[index];
          final isActive = index == _index;
          return ClipRect(
            key: ValueKey(item.key),
            child: item.isVideo
                ? GalleryVideoPage(item: item, isActive: isActive)
                : GalleryImagePage(
                    item: item,
                    isActive: isActive,
                    rotateSignal: _rotateSignal,
                  ),
          );
        },
      ),
    ),
  );
}