聊天时间分割线优化与缩略图生成菜单

Widget messageContent = Column(
  key: ValueKey(message.id),
  children: [
    // 日期分隔符在消息上方（表示"从这里开始是新的一天"）
    if (showDateSeparator) DateSeparator(date: message.createdAt.toLocal()),
    _buildMessageBubble(message),
  ],
);

Container(
  padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 6),
  decoration: BoxDecoration(
    color: Colors.blue.withValues(alpha: 0.1),
    borderRadius: BorderRadius.circular(12),
  ),
  child: Text(formattedDate, style: TextStyle(color: Colors.blue)),
)

Row(
  children: [
    Expanded(child: Container(height: 1, color: lineColor)),
    Padding(
      padding: const EdgeInsets.symmetric(horizontal: 12),
      child: Text(formattedDate, style: TextStyle(color: textColor, fontSize: 12)),
    ),
    Expanded(child: Container(height: 1, color: lineColor)),
  ],
)

String _formatDate(DateTime date) {
  final now = DateTime.now();
  final localDate = date.isUtc ? date.toLocal() : date;
  final today = DateTime(now.year, now.month, now.day);
  final dateOnly = DateTime(localDate.year, localDate.month, localDate.day);
  final diff = today.difference(dateOnly).inDays;
 
  if (diff == 0) return '今天';
  if (diff == 1) return '昨天';
  if (diff < 7 && localDate.weekday < now.weekday) {
    const weekdays = ['周一', '周二', '周三', '周四', '周五', '周六', '周日'];
    return weekdays[localDate.weekday - 1];
  }
  if (now.year == localDate.year) {
    const weekdays = ['周一', '周二', '周三', '周四', '周五', '周六', '周日'];
    return '${localDate.month}月${localDate.day}日 ${weekdays[localDate.weekday - 1]}';
  }
  return '${localDate.year}年${localDate.month}月${localDate.day}日';
}

Future<void> init() async {
  try {
    // 使用应用文档目录而不是临时目录，避免系统清理缓存
    final dir = await getApplicationDocumentsDirectory();
    _baseDir = Directory(path.join(dir.path, 'thumbnail_cache'));
    if (!await _baseDir!.exists()) {
      await _baseDir!.create(recursive: true);
    }
  } catch (e) {
    debugPrint('ThumbnailCacheManager init error: $e');
  }
}

// 1. 删除可能存在的旧缩略图
await appState.api.deleteThumbnail(fileId);
 
// 2. 触发后端按需生成（autoGen: true）
final result = await appState.api.getThumbnailWithInfo(fileId, autoGen: true);
 
// 3. 更新本地缓存
if (result.imageData != null) {
  final thumbData = Uint8List.fromList(result.imageData!);
  await ThumbnailCacheManager().saveThumbnail(fileId, thumbData);
  _thumbnailCache.put(fileId, thumbData);
}

// 1. 确认对话框（提示会消耗流量）
final confirm = await showDialog<bool>(
  context: context,
  builder: (ctx) => AlertDialog(
    title: const Text('生成视频缩略图'),
    content: const Text('需要下载视频数据来生成缩略图，这可能会消耗一些流量。是否继续？'),
    actions: [
      TextButton(onPressed: () => Navigator.pop(ctx, false), child: const Text('取消')),
      TextButton(onPressed: () => Navigator.pop(ctx, true), child: const Text('继续')),
    ],
  ),
);
 
if (confirm != true) return;
 
// 2. 使用流式 URL 生成缩略图
final streamUrl = appState.api.getStreamUrl(fileId);
final headers = appState.api.getStreamHeaders();
thumbData = await VideoThumbnailService().generateFromUrl(streamUrl, headers);
 
// 3. 上传到后端
if (thumbData != null) {
  await appState.api.uploadThumbnail(fileId, thumbData);
}
 
// 4. 更新本地缓存
await ThumbnailCacheManager().saveThumbnail(fileId, thumbData);
_thumbnailCache.put(fileId, thumbData);

// files_page.dart
Future<void> _initThumbnailCache() async {
  await ThumbnailCacheManager().init();  // 只有这里调用了 init()
}

// app_state.dart 启动流程
_initCoreAndNetwork()
  ↓
_loadPreferences()
  ↓
_loadS3Config()
  ↓
_applyS3Config(config)  // 调用 setS3ConfigId()
  ↓
ThumbnailCacheManager().setS3ConfigId(config.id)

Future<void> setS3ConfigId(String? s3ConfigId) async {
  _currentS3ConfigId = s3ConfigId;
  await _updateCacheDir();  // 调用 _updateCacheDir
}
 
Future<void> _updateCacheDir() async {
  if (_baseDir == null) return;  // 如果 init() 还没调用，_baseDir 为 null，直接返回！
  // ... 设置 _cacheDir
}

Future<void> _ensureInit() async {
  if (_initialized && _cacheDir != null) return;
  await init();  // 没有并发保护！
}

// app_state.dart
Future<void> _loadS3Config() async {
  // 确保缩略图缓存管理器先初始化，再设置 S3 配置 ID
  // 否则 setS3ConfigId 调用时 _baseDir 为 null，导致缓存目录设置失败
  await ThumbnailCacheManager().init();
 
  final activeConfig = await db.getActiveS3Config();
  if (activeConfig != null) {
    _applyS3Config(activeConfig);
  }
}

// thumbnail_cache.dart
Completer<void>? _initCompleter;
 
Future<void> init() async {
  // 如果已经初始化完成，直接返回
  if (_initialized && _baseDir != null) {
    return;
  }
 
  // 如果正在初始化，等待完成
  if (_initCompleter != null) {
    await _initCompleter!.future;
    return;
  }
 
  // 开始初始化
  _initCompleter = Completer<void>();
 
  try {
    final dir = await getApplicationDocumentsDirectory();
    _baseDir = Directory(path.join(dir.path, 'thumbnail_cache'));
    // ...
  } finally {
    _initCompleter!.complete();
    _initCompleter = null;
  }
}

Future<void> setS3ConfigId(String? s3ConfigId) async {
  // ...
  debugPrint('[ThumbnailCache] S3 config ID set to: $s3ConfigId, cacheDir: ${_cacheDir?.path}');
}
 
Future<void> init() async {
  // ...
  debugPrint('[ThumbnailCache] Initialized. baseDir: ${_baseDir?.path}, cacheDir: ${_cacheDir?.path}');
}