import 'package:shared_preferences/shared_preferences.dart';

/// 本地记录各会话已同步到的最大 seq，断线重连后用于 gap fill。
class ImSeqStore {
  ImSeqStore._();
  static SharedPreferences? _p;

  static Future<void> ensure() async {
    _p ??= await SharedPreferences.getInstance();
  }

  static Future<int> lastSeq(String conversationId) async {
    if (conversationId.isEmpty) return 0;
    await ensure();
    return _p?.getInt('im.seq.$conversationId') ?? 0;
  }

  static Future<void> setLastSeq(String conversationId, int seq) async {
    if (conversationId.isEmpty || seq <= 0) return;
    await ensure();
    final prev = _p?.getInt('im.seq.$conversationId') ?? 0;
    if (seq > prev) await _p!.setInt('im.seq.$conversationId', seq);
  }

  static Future<void> applyItems(String conversationId, Iterable<Map<String, dynamic>> items) async {
    var max = 0;
    for (final e in items) {
      final s = (e['seq'] as num?)?.toInt() ?? 0;
      if (s > max) max = s;
    }
    if (max > 0) await setLastSeq(conversationId, max);
  }
}