// lib/metadata/metadata_service.dart
import 'dart:io';
import 'metadata_model.dart';
import 'metadata_reader.dart';
import 'metadata_normalizer.dart';
import 'metadata_cache.dart';

class MetadataService {
  static final MetadataService _instance = MetadataService._internal();
  factory MetadataService() => _instance;
  MetadataService._internal();

  final MetadataReader _reader = MetadataReader();
  final MetadataNormalizer _normalizer = MetadataNormalizer();
  final MetadataCache _cache = MetadataCache();

  /// 获取歌曲的最终元数据（优先缓存，否则读取文件）
  Future<FinalMetadata> getMetadata({
    required String filePath,
    required String fileName,
    required String fileId,
    bool forceRefresh = false,
  }) async {
    // 1. 尝试从缓存读取
    if (!forceRefresh) {
      final cached = await _cache.get(fileId);
      if (cached != null && cached.isNotEmpty) {
        return cached;
      }
    }

    // 2. 检查文件是否存在
    final file = File(filePath);
    if (!await file.exists()) {
      // 文件不存在，返回基于文件名的推断
      return _fallbackFromFileName(fileName);
    }

    // 3. 从文件读取原始元数据
    final raw = await _reader.readRawMetadata(file);

    // 4. 标准化
    final normalized = _normalizer.normalize(
      raw,
      fileName: fileName,
      filePath: filePath,
    );

    // 5. 评估（第一阶段直接接受）
    final history = await _cache.getHistory(normalized.artist, limit: 10);
    final candidate = _normalizer.evaluate(normalized, history);

    // 6. 决策
    final finalMetadata = _normalizer.decide(candidate);

    // 7. 写入缓存
    if (finalMetadata.isNotEmpty) {
      await _cache.put(fileId, finalMetadata);
    }

    return finalMetadata;
  }

  /// Fallback：从文件名推断
  FinalMetadata _fallbackFromFileName(String fileName) {
    final dotIndex = fileName.lastIndexOf('.');
    final title = dotIndex > 0 ? fileName.substring(0, dotIndex) : fileName;
    return FinalMetadata(
      title: title,
      artist: '未知艺术家',
      source: 'filename',
    );
  }
}