import 'dart:convert';
import 'dart:io';
import 'dart:typed_data';

import 'package:crypto/crypto.dart';
import 'package:path_provider/path_provider.dart';
import 'package:video_thumbnail/video_thumbnail.dart';

/// 视频封面缓存：优先从本地读取，未命中则生成并缓存
class VideoThumbnailCache {
  VideoThumbnailCache._();
  static final VideoThumbnailCache _instance = VideoThumbnailCache._();
  static VideoThumbnailCache get instance => _instance;

  static const int _maxWidth = 400;
  static const int _quality = 75;

  Future<Uint8List?> getThumbnail(String videoUrl) async {
    final key = _cacheKey(videoUrl);
    final cacheDir = await _getCacheDir();
    final file = File('${cacheDir.path}/$key.jpg');

    if (await file.exists()) {
      return file.readAsBytes();
    }

    try {
      final path = await VideoThumbnail.thumbnailFile(
        video: videoUrl,
        thumbnailPath: cacheDir.path,
        imageFormat: ImageFormat.JPEG,
        maxWidth: _maxWidth,
        quality: _quality,
      );
      if (path != null) {
        final cached = File(path);
        final bytes = await cached.readAsBytes();
        if (cached.path != file.path) {
          await file.writeAsBytes(bytes);
          cached.deleteSync();
        }
        return bytes;
      }
    } catch (_) {}
    return null;
  }

  String _cacheKey(String url) {
    final bytes = utf8.encode(url);
    final digest = md5.convert(bytes);
    return digest.toString();
  }

  Directory? _cacheDir;
  Future<Directory> _getCacheDir() async {
    _cacheDir ??= await getTemporaryDirectory();
    final dir = Directory('${_cacheDir!.path}/video_thumbnails');
    if (!await dir.exists()) {
      await dir.create(recursive: true);
    }
    return dir;
  }
}