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app/lib/core/media/download_manager.dart

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+import 'dart:convert';
+import 'dart:io';
+
+import 'package:dio/dio.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:path/path.dart' as p;
+
+import '../../models/video_item.dart';
+import 'local_media_server.dart';
+
+/// 已下载视频元数据（持久化在 downloads/<videoId>/meta.json）
+class DownloadItem {
+  DownloadItem({
+    required this.videoId,
+    required this.title,
+    required this.coverUrl,
+    required this.duration,
+    required this.sizeBytes,
+    required this.mp4,
+    required this.createdAt,
+  });
+
+  final int videoId;
+  final String title;
+  final String coverUrl;
+  final int duration; // 秒
+  final int sizeBytes;
+  final bool mp4;
+  final int createdAt; // 毫秒时间戳
+
+  /// 本地播放地址（经 LocalMediaServer /local 路由，支持 Range）
+  String get playUrl =>
+      LocalMediaServer.I.localPlayUrl(videoId, mp4: mp4);
+
+  Map<String, dynamic> toJson() => {
+        'video_id': videoId,
+        'title': title,
+        'cover_url': coverUrl,
+        'duration': duration,
+        'size_bytes': sizeBytes,
+        'mp4': mp4,
+        'created_at': createdAt,
+      };
+
+  factory DownloadItem.fromJson(Map<String, dynamic> j) => DownloadItem(
+        videoId: j['video_id'] as int,
+        title: (j['title'] as String?) ?? '',
+        coverUrl: (j['cover_url'] as String?) ?? '',
+        duration: (j['duration'] as num?)?.toInt() ?? 0,
+        sizeBytes: (j['size_bytes'] as num?)?.toInt() ?? 0,
+        mp4: j['mp4'] as bool? ?? false,
+        createdAt: (j['created_at'] as num?)?.toInt() ?? 0,
+      );
+}
+
+/// 下载任务状态机：value 为 0..1 进度；done/error 用独立集合
+class DownloadsState {
+  const DownloadsState({
+    this.progress = const {},
+    this.errors = const {},
+    this.items = const [],
+  });
+
+  final Map<int, double> progress; // 下载中
+  final Map<int, String> errors; // 失败信息
+  final List<DownloadItem> items; // 已完成（按下载时间倒序）
+
+  DownloadsState copyWith({
+    Map<int, double>? progress,
+    Map<int, String>? errors,
+    List<DownloadItem>? items,
+  }) =>
+      DownloadsState(
+        progress: progress ?? this.progress,
+        errors: errors ?? this.errors,
+        items: items ?? this.items,
+      );
+}
+
+class DownloadManager extends StateNotifier<DownloadsState> {
+  DownloadManager() : super(const DownloadsState());
+
+  final Dio _dio = Dio(BaseOptions(
+    connectTimeout: const Duration(seconds: 15),
+    receiveTimeout: const Duration(minutes: 10),
+    headers: {
+      'User-Agent': 'Mozilla/5.0 (Linux; Android 13) AppleWebKit/537.36 '
+          '(KHTML, like Gecko) Chrome/120.0 Mobile Safari/537.36',
+    },
+  ));
+
+  final Map<int, CancelToken> _cancel = {};
+
+  bool isDownloaded(int videoId) =>
+      state.items.any((e) => e.videoId == videoId);
+  bool isDownloading(int videoId) => state.progress.containsKey(videoId);
+
+  /// 启动时扫描下载目录恢复列表
+  Future<void> init() async {
+    final dir = LocalMediaServer.I.downloadsDir;
+    final items = <DownloadItem>[];
+    await for (final e in dir.list()) {
+      if (e is! Directory) continue;
+      final meta = File(p.join(e.path, 'meta.json'));
+      if (!await meta.exists()) continue;
+      try {
+        items.add(DownloadItem.fromJson(
+            jsonDecode(await meta.readAsString()) as Map<String, dynamic>));
+      } catch (_) {}
+    }
+    items.sort((a, b) => b.createdAt.compareTo(a.createdAt));
+    state = state.copyWith(items: items);
+  }
+
+  /// 开始下载（已在下载/已下载则忽略）
+  Future<void> start(VideoItem item) async {
+    if (isDownloading(item.videoId) || isDownloaded(item.videoId)) return;
+
+    final dir = Directory(p.join(
+        LocalMediaServer.I.downloadsDir.path, '${item.videoId}'));
+    await dir.create(recursive: true);
+    final cancel = CancelToken();
+    _cancel[item.videoId] = cancel;
+    _setProgress(item.videoId, 0);
+
+    try {
+      final isMp4 = item.videoUrl.contains('.mp4') &&
+          !item.videoUrl.contains('m3u8');
+      int size;
+      if (isMp4) {
+        size = await _downloadMp4(item.videoUrl, dir, item.videoId, cancel);
+      } else {
+        size = await _downloadHls(item.videoUrl, dir, item.videoId, cancel);
+      }
+
+      final meta = DownloadItem(
+        videoId: item.videoId,
+        title: item.title,
+        coverUrl: item.coverUrl,
+        duration: item.duration,
+        sizeBytes: size,
+        mp4: isMp4,
+        createdAt: DateTime.now().millisecondsSinceEpoch,
+      );
+      await File(p.join(dir.path, 'meta.json'))
+          .writeAsString(jsonEncode(meta.toJson()));
+
+      final progress = Map<int, double>.from(state.progress)
+        ..remove(item.videoId);
+      state = state.copyWith(
+        progress: progress,
+        items: [meta, ...state.items],
+      );
+    } catch (e) {
+      // 失败/取消：清掉半成品目录
+      try {
+        await dir.delete(recursive: true);
+      } catch (_) {}
+      final progress = Map<int, double>.from(state.progress)
+        ..remove(item.videoId);
+      if (e is DioException && CancelToken.isCancel(e)) {
+        state = state.copyWith(progress: progress);
+      } else {
+        final errors = Map<int, String>.from(state.errors)
+          ..[item.videoId] = '下载失败，请重试';
+        state = state.copyWith(progress: progress, errors: errors);
+      }
+      rethrow;
+    } finally {
+      _cancel.remove(item.videoId);
+    }
+  }
+
+  void cancel(int videoId) => _cancel[videoId]?.cancel();
+
+  Future<void> delete(int videoId) async {
+    _cancel[videoId]?.cancel();
+    final dir = Directory(
+        p.join(LocalMediaServer.I.downloadsDir.path, '$videoId'));
+    try {
+      await dir.delete(recursive: true);
+    } catch (_) {}
+    state = state.copyWith(
+      items: state.items.where((e) => e.videoId != videoId).toList(),
+    );
+  }
+
+  // ---------- MP4 ----------
+
+  Future<int> _downloadMp4(
+      String url, Directory dir, int videoId, CancelToken cancel) async {
+    final file = File(p.join(dir.path, 'video.mp4'));
+    await _dio.download(
+      url,
+      file.path,
+      cancelToken: cancel,
+      onReceiveProgress: (r, t) {
+        if (t > 0) _setProgress(videoId, r / t);
+      },
+    );
+    return file.length();
+  }
+
+  // ---------- HLS ----------
+
+  /// 拉取 m3u8 → 下载 key + 全部 ts → 改写为本地相对引用
+  Future<int> _downloadHls(
+      String url, Directory dir, int videoId, CancelToken cancel) async {
+    var playlist = (await _dio.get<String>(url, cancelToken: cancel)).data ?? '';
+    var base = Uri.parse(url);
+
+    // master playlist（多变体）：取第一个变体再拉一次
+    if (playlist.contains('#EXT-X-STREAM-INF')) {
+      final variant = const LineSplitter()
+          .convert(playlist)
+          .firstWhere((l) => l.trim().isNotEmpty && !l.startsWith('#'),
+              orElse: () => '');
+      if (variant.isEmpty) throw Exception('空变体列表');
+      final variantUrl = base.resolve(variant.trim()).toString();
+      playlist =
+          (await _dio.get<String>(variantUrl, cancelToken: cancel)).data ?? '';
+      base = Uri.parse(variantUrl);
+    }
+
+    final lines = const LineSplitter().convert(playlist);
+    final segUrls = <Uri>[
+      for (final l in lines)
+        if (l.trim().isNotEmpty && !l.trim().startsWith('#'))
+          base.resolve(l.trim()),
+    ];
+    if (segUrls.isEmpty) throw Exception('无分片');
+
+    var total = 0;
+    var done = 0;
+
+    // key（可能多个，逐标签改写时按出现顺序对应）
+    final keyUris = <String>[];
+    for (final l in lines) {
+      for (final m in RegExp(r'URI="([^"]+)"').allMatches(l)) {
+        final abs = base.resolve(m.group(1)!).toString();
+        if (!keyUris.contains(abs)) keyUris.add(abs);
+      }
+    }
+    final keyNames = <String, String>{};
+    for (var i = 0; i < keyUris.length; i++) {
+      final name = i == 0 ? 'key.bin' : 'key_$i.bin';
+      final bytes = (await _dio.get<List<int>>(keyUris[i],
+              cancelToken: cancel,
+              options: Options(responseType: ResponseType.bytes)))
+          .data;
+      if (bytes == null || bytes.isEmpty) throw Exception('密钥下载失败');
+      await File(p.join(dir.path, name)).writeAsBytes(bytes);
+      keyNames[keyUris[i]] = name;
+      total += bytes.length;
+    }
+
+    // ts 分片：4 并发
+    const concurrency = 4;
+    for (var i = 0; i < segUrls.length; i += concurrency) {
+      final batch = segUrls.sublist(
+          i, (i + concurrency).clamp(0, segUrls.length));
+      final results = await Future.wait(batch.map((u) => _dio.get<List<int>>(
+          u.toString(),
+          cancelToken: cancel,
+          options: Options(responseType: ResponseType.bytes))));
+      for (var j = 0; j < batch.length; j++) {
+        final bytes = results[j].data;
+        if (bytes == null || bytes.isEmpty) throw Exception('分片下载失败');
+        await File(p.join(dir.path, 'seg_${i + j}.ts')).writeAsBytes(bytes);
+        total += bytes.length;
+        done++;
+      }
+      _setProgress(videoId, done / segUrls.length);
+    }
+
+    // 改写 playlist 为本地相对引用
+    var segIndex = 0;
+    final out = StringBuffer();
+    for (final raw in lines) {
+      final line = raw.trim();
+      if (line.isEmpty) continue;
+      if (line.startsWith('#')) {
+        out.writeln(line.replaceAllMapped(RegExp(r'URI="([^"]+)"'), (m) {
+          final abs = base.resolve(m.group(1)!).toString();
+          return 'URI="${keyNames[abs] ?? m.group(1)!}"';
+        }));
+      } else {
+        out.writeln('seg_${segIndex++}.ts');
+      }
+    }
+    await File(p.join(dir.path, 'index.m3u8')).writeAsString(out.toString());
+    return total;
+  }
+
+  void _setProgress(int videoId, double value) {
+    final progress = Map<int, double>.from(state.progress);
+    progress[videoId] = value;
+    state = state.copyWith(progress: progress);
+  }
+}
+
+final downloadManagerProvider =
+    StateNotifierProvider<DownloadManager, DownloadsState>(
+        (ref) => DownloadManager());