import 'dart:convert';

import 'package:shared_preferences/shared_preferences.dart';

const String _shareIntakeDebugLogKey = 'share_intake_debug_log_v1';
const int _maxShareIntakeDebugEvents = 40;

class ShareIntakeDebugEvent {
  const ShareIntakeDebugEvent({
    required this.at,
    required this.stage,
    required this.message,
  });

  factory ShareIntakeDebugEvent.fromJson(Map<String, dynamic> json) {
    return ShareIntakeDebugEvent(
      at: DateTime.parse(
        json['at'] as String? ?? DateTime.now().toUtc().toIso8601String(),
      ).toLocal(),
      stage: json['stage'] as String? ?? 'unknown',
      message: json['message'] as String? ?? '',
    );
  }

  final DateTime at;
  final String stage;
  final String message;

  Map<String, dynamic> toJson() {
    return <String, dynamic>{
      'at': at.toUtc().toIso8601String(),
      'stage': stage,
      'message': message,
    };
  }
}

class ShareIntakeDebugLog {
  const ShareIntakeDebugLog();

  Future<List<ShareIntakeDebugEvent>> read() async {
    final SharedPreferences prefs = await SharedPreferences.getInstance();
    final String? raw = prefs.getString(_shareIntakeDebugLogKey);
    if (raw == null || raw.isEmpty) {
      return const <ShareIntakeDebugEvent>[];
    }
    try {
      final List<dynamic> items = jsonDecode(raw) as List<dynamic>;
      return items
          .whereType<Map<String, dynamic>>()
          .map(ShareIntakeDebugEvent.fromJson)
          .toList(growable: false);
    } on FormatException {
      return const <ShareIntakeDebugEvent>[];
    }
  }

  Future<void> record(String stage, String message) async {
    final SharedPreferences prefs = await SharedPreferences.getInstance();
    final List<ShareIntakeDebugEvent> current = await read();
    final List<ShareIntakeDebugEvent> next = <ShareIntakeDebugEvent>[
      ShareIntakeDebugEvent(at: DateTime.now(), stage: stage, message: message),
      ...current,
    ].take(_maxShareIntakeDebugEvents).toList(growable: false);
    await prefs.setString(
      _shareIntakeDebugLogKey,
      jsonEncode(
        next
            .map((ShareIntakeDebugEvent event) => event.toJson())
            .toList(growable: false),
      ),
    );
  }

  Future<void> clear() async {
    final SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.remove(_shareIntakeDebugLogKey);
  }
}