import 'dart:convert';

import 'package:shared_preferences/shared_preferences.dart';

/// 聊天消息的本地副本。云端只保留 7 天，客户端仍可查看本机历史消息。
class ChatLocalStore {
  ChatLocalStore._();

  static Future<List<Map<String, dynamic>>> load(String conversationId) async {
    if (conversationId.isEmpty) return [];
    final p = await SharedPreferences.getInstance();
    final raw = p.getString('im.local.$conversationId');
    if (raw == null || raw.isEmpty) return [];
    try {
      final list = jsonDecode(raw);
      if (list is! List) return [];
      return list.whereType<Map>().map((e) => Map<String, dynamic>.from(e)).toList();
    } catch (_) {
      return [];
    }
  }

  static Future<void> save(String conversationId, List<Map<String, dynamic>> items) async {
    if (conversationId.isEmpty) return;
    final p = await SharedPreferences.getInstance();
    final durable = items.where((e) => e['_pending'] != true).map((e) {
      final copy = Map<String, dynamic>.from(e)..remove('_pending');
      return copy;
    }).toList();
    await p.setString('im.local.$conversationId', jsonEncode(durable));
  }
}