数据和测试案例按照架构来处理

apps/im_app/lib/features/chat/usecases/insert_users_use_case.dart

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+import 'package:im_app/domain/entities/user.dart';
+import 'package:im_app/domain/repositories/user_repository.dart';
+
+/// 批量插入用户用例
+///
+/// ## 职责
+/// - 封装用户插入的业务规则
+/// - 去重（uid 相同时保留最后一个）
+/// - 分批插入，避免单次写入过大
+///
+/// ## 数据流
+/// ```
+/// ViewModel
+///   → InsertUsersUseCase.execute(users)
+///     → 去重
+///     → UserRepository.saveUsers(chunk)  ← 分批写入
+///     → onProgress(completed, total)     ← 可选进度回调
+///   ← 实际插入数量
+/// ```
+class InsertUsersUseCase {
+  final UserRepository _repo;
+  static const _chunkSize = 200;
+
+  InsertUsersUseCase({required UserRepository userRepository})
+    : _repo = userRepository;
+
+  /// 批量插入用户
+  ///
+  /// [users] 要插入的用户列表
+  /// [onProgress] 可选回调，每批完成后触发
+  ///
+  /// 返回实际插入数量
+  Future<int> execute(
+    List<User> users, {
+    void Function(int completed, int total, List<User> chunk)? onProgress,
+  }) async {
+    if (users.isEmpty) return 0;
+
+    final deduped = {for (final u in users) u.uid: u}.values.toList();
+    final total = deduped.length;
+    int completed = 0;
+
+    while (completed < total) {
+      final end = (completed + _chunkSize).clamp(0, total);
+      final chunk = deduped.sublist(completed, end);
+
+      await _repo.saveUsers(chunk);
+      completed += chunk.length;
+
+      onProgress?.call(completed, total, chunk);
+    }
+
+    return completed;
+  }
+}