metadata读取能力已达成，接下来会顺着路径完成部分缓存指针设计

lib/metadata/metadata_service.dart

@@ -1,38 +1,76 @@
 // lib/metadata/metadata_service.dart
+// ⭐ 移除未使用的 import 'dart:io';
+import 'package:flutter/foundation.dart'; // ⭐ 添加
 import 'metadata_model.dart';
+import 'metadata_reader.dart';
+import 'metadata_normalizer.dart';
 import 'metadata_cache.dart';
+import 'file_provider.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();
 
-  /// 临时版本：不进行实际文件读取，只返回基于文件名的 fallback
+  FileProvider _getProvider(String url) {
+    if (url.startsWith('http://') || url.startsWith('https://')) {
+      return WebDAVFileProvider();
+    }
+    return LocalFileProvider();
+  }
+
   Future<FinalMetadata> getMetadata({
     required String url,
     required String fileName,
     required String fileId,
     bool forceRefresh = false,
   }) async {
-    // 1. 检查缓存（如果有）
+    // 1. 检查缓存
     if (!forceRefresh) {
       final cached = await _cache.get(fileId);
       if (cached != null && cached.isNotEmpty) {
+        debugPrint('📦 [MetadataService] cache hit: ${cached.title}');
         return cached;
       }
     }
 
-    // 2. 暂时不读取文件，直接 fallback
-    final fallback = _fallbackFromFileName(fileName);
+    // 2. 获取文件
+    final provider = _getProvider(url);
+    final file = await provider.getFile(url);
 
-    // 3. 缓存结果（即使 fallback 也缓存，避免频繁调用）
-    if (fallback.isNotEmpty) {
-      await _cache.put(fileId, fallback);
+    if (file == null || !await file.exists()) {
+      debugPrint(
+          '⚠️ [MetadataService] file not available, using filename fallback');
+      return _fallbackFromFileName(fileName);
     }
 
-    return fallback;
+    // 3. 读取 metadata
+    final raw = await _reader.readRawMetadata(file);
+
+    // 4. 标准化
+    final normalized = _normalizer.normalize(
+      raw,
+      fileName: fileName,
+      filePath: url,
+    );
+
+    // 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);
+    final finalMetadata = _normalizer.decide(candidate);
+
+    // 6. 缓存
+    if (finalMetadata.isNotEmpty) {
+      await _cache.put(fileId, finalMetadata);
+      debugPrint(
+          '✅ [MetadataService] metadata saved: ${finalMetadata.title} - ${finalMetadata.artist}');
+    }
+
+    return finalMetadata;
   }
 
   FinalMetadata _fallbackFromFileName(String fileName) {