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

import 'package:cached_network_image/cached_network_image.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter_cache_manager/flutter_cache_manager.dart';

import '../../api/marianumcloud/webdav/webdav_api.dart';
import '../../model/endpoint_data.dart';
import '../../session/session_manager.dart';
import '../../utils/downloads/download_manager.dart';
import '../../utils/screen_bound_image.dart';
import 'gallery_item.dart';

/// Server-rendered preview edge for the gallery; Nextcloud derives it from the
/// max preview it already keeps for the thumbnails.
const int _previewSize = 2048;

/// Originals the gallery loaded on its own — outside [DownloadManager], so no
/// notification or tray entry. Wiped whenever an account stops being active.
class GalleryOriginals extends ChangeNotifier {
  GalleryOriginals._();
  static final GalleryOriginals instance = GalleryOriginals._();

  static final CacheManager _images = CacheManager(
    Config(
      'galleryOriginals',
      stalePeriod: const Duration(days: 14),
      maxNrOfCacheObjects: 150,
    ),
  );

  // Videos are large; keep only a handful around.
  static final CacheManager _videos = CacheManager(
    Config(
      'galleryVideos',
      stalePeriod: const Duration(days: 3),
      maxNrOfCacheObjects: 10,
    ),
  );

  final Map<String, _Flight> _flights = {};

  static CacheManager _managerFor(GalleryItem item) =>
      item.isVideo ? _videos : _images;

  static String _cacheKey(GalleryItem item) =>
      '${SessionManager().requireNextcloud().username}:${item.file.path}'
      ':${item.eTag ?? ''}';

  static String _webdavUrl(String remotePath) =>
      '${WebdavApi.buildWebdavUrl()}'
      '${Uri.encodeComponent(remotePath).replaceAll('%2F', '/')}';

  /// Download progress (0–1, null while the size is unknown) of a running
  /// original download, or null when none runs.
  ValueListenable<double?>? progressOf(GalleryItem item) =>
      _flights[_cacheKey(item)]?.progress;

  Future<File?> cached(GalleryItem item) async {
    final info = await _managerFor(item).getFileFromCache(_cacheKey(item));
    final file = info?.file;
    return file != null && file.existsSync() ? file : null;
  }

  /// Loads the original once; parallel callers share the same download.
  Future<File> load(GalleryItem item) {
    final key = _cacheKey(item);
    final running = _flights[key];
    if (running != null) return running.completer.future;

    final flight = _Flight();
    _flights[key] = flight;
    notifyListeners();
    final epoch = SessionManager().sessionEpoch;
    final manager = _managerFor(item);
    flight.subscription = manager
        .getFileStream(
          _webdavUrl(item.file.path),
          key: key,
          headers: SessionManager().requireNextcloud().authHeaders,
          withProgress: true,
        )
        .listen(
          (response) {
            if (response is DownloadProgress) {
              flight.progress.value = response.progress;
            } else if (response is FileInfo) {
              if (!SessionManager().isCurrentSession(epoch)) {
                unawaited(manager.removeFile(key));
                _finish(key, error: StateError('Konto gewechselt'));
                return;
              }
              _finish(key, file: response.file);
            }
          },
          onError: (Object e) => _finish(key, error: e),
          cancelOnError: true,
        );
    return flight.completer.future;
  }

  void _finish(String key, {File? file, Object? error}) {
    final flight = _flights.remove(key);
    if (flight == null) return;
    unawaited(flight.cancel());
    if (file != null) {
      flight.completer.complete(file);
    } else {
      flight.completer.completeError(
        error ?? StateError('Download fehlgeschlagen'),
      );
    }
    notifyListeners();
    scheduleMicrotask(flight.progress.dispose);
  }

  /// Copies the original under its real file name (into the downloads folder,
  /// which [SessionWipe] clears) — share sheets and "Öffnen mit" need the name
  /// and extension, the cache file has neither.
  Future<String> namedCopy(GalleryItem item) async {
    final source = await cached(item) ?? await load(item);
    final dir = await DownloadManager.downloadsDirectory();
    await dir.create(recursive: true);
    final target = File('${dir.path}/${item.file.name}');
    await source.copy(target.path);
    return target.path;
  }

  Future<void> clear() async {
    for (final key in _flights.keys.toList()) {
      _finish(key, error: StateError('Abgebrochen'));
    }
    await _images.emptyCache();
    await _videos.emptyCache();
  }
}

class _Flight {
  final Completer<File> completer = Completer<File>();
  final ValueNotifier<double?> progress = ValueNotifier(null);
  StreamSubscription<FileResponse>? subscription;

  Future<void> cancel() async => subscription?.cancel();
}

/// Screen-sized server preview. One instance per item and size, so the
/// viewer's precache and the page's image hit the same cache entry.
ImageProvider galleryPreviewProvider(BuildContext context, GalleryItem item) {
  final fileId = item.file.fileId;
  final url = fileId != null
      ? '${EndpointData().nextcloud().origin()}/index.php/core/preview'
            '?fileId=$fileId&x=$_previewSize&y=$_previewSize&a=1'
      : '${EndpointData().nextcloud().origin()}/index.php/core/preview.png'
            '?file=${Uri.encodeQueryComponent(item.file.path)}'
            '&x=$_previewSize&y=$_previewSize&a=1';
  return screenBoundImage(
    context,
    CachedNetworkImageProvider(
      url,
      headers: SessionManager().requireNextcloud().authHeaders,
    ),
  );
}