// lib/metadata/file_provider.dart
import 'dart:io';
import 'package:flutter/foundation.dart';
import 'package:path_provider/path_provider.dart';
import 'package:dio/dio.dart';
import '../services/webdav_service.dart';
import '../utils/song_key.dart';

abstract class FileProvider {
  Future<File?> getFile(String url);
}

class WebDAVFileProvider implements FileProvider {
  /// 只为读标签取文件头部，绝不整文件下载。
  /// 之前用 dio.download 会把整首歌拉到临时目录，和 mpv 的流式播放抢带宽，
  /// 20Mbps 的 FRP 链路上尤其明显（表现为流量很高但缓冲一直为 0）。
  static const int _maxBytes = 2 * 1024 * 1024;

  /// 切歌时取消上一次未完成的下载，避免多个下载叠加占满带宽。
  static CancelToken? _activeToken;

  final Dio _dio = Dio();

  @override
  Future<File?> getFile(String url) async {
    try {
      final cacheDir = await getTemporaryDirectory();
      final cachePath = '${cacheDir.path}/metadata_${songKeyForUrl(url)}.part';
      final cacheFile = File(cachePath);

      // 1. 命中本地缓存（头部文件同样按 24h 过期）
      if (await cacheFile.exists()) {
        final stat = await cacheFile.stat();
        if (stat.size > 0 &&
            DateTime.now().difference(stat.modified).inSeconds < 86400) {
          return cacheFile;
        }
      }

      // 2. 认证头
      final headers = await WebDAVService.instance.getAuthHeaders();
      if (headers.isEmpty) return null;

      // 3. 取消上一次未完成的下载
      _activeToken?.cancel('superseded');
      final token = CancelToken();
      _activeToken = token;

      // 4. 只请求前 2MB
      final response = await _dio.get<ResponseBody>(
        url,
        cancelToken: token,
        options: Options(
          headers: {
            ...headers,
            'Range': 'bytes=0-${_maxBytes - 1}',
          },
          responseType: ResponseType.stream,
          receiveTimeout: const Duration(seconds: 15),
          sendTimeout: const Duration(seconds: 10),
          followRedirects: true,
        ),
      );

      final body = response.data;
      if (body == null) return null;

      // 5. 写入临时文件（最多 _maxBytes）
      final sink = cacheFile.openWrite();
      var written = 0;
      try {
        await for (final chunk in body.stream) {
          final remain = _maxBytes - written;
          if (remain <= 0) break;
          final data =
              chunk.lengthInBytes > remain ? chunk.sublist(0, remain) : chunk;
          sink.add(data);
          written += data.lengthInBytes;
          if (written >= _maxBytes) break;
        }
      } finally {
        await sink.flush();
        await sink.close();
      }

      if (written == 0) {
        try {
          await cacheFile.delete();
        } catch (_) {}
        return null;
      }

      debugPrint(
          '📦 [WebDAVFileProvider] 取头部 ${(written / 1024).toStringAsFixed(0)}KB'
          '（上限 ${_maxBytes ~/ 1024}KB，不再整文件下载）');
      return cacheFile;
    } on DioException catch (e) {
      if (CancelToken.isCancel(e)) {
        debugPrint('↩️ [WebDAVFileProvider] 下载已取消（切歌触发）');
        return null;
      }
      debugPrint('⚠️ [WebDAVFileProvider] download failed: $e');
      return null;
    } catch (e) {
      debugPrint('⚠️ [WebDAVFileProvider] download failed: $e');
      return null;
    }
  }

  /// 主动取消进行中的元数据下载（切歌时可由上层调用）。
  static void cancelActive() {
    _activeToken?.cancel('superseded');
    _activeToken = null;
  }
}

class LocalFileProvider implements FileProvider {
  @override
  Future<File?> getFile(String url) async {
    final file = File(url);
    if (await file.exists()) {
      return file;
    }
    return null;
  }
}