import 'package:flutter/foundation.dart';
import 'package:relationship_saver/integrations/backend/models/backend_models.dart';

/// Persisted state for sync queue and cursor progression.
@immutable
class SyncState {
  const SyncState({
    this.cursor,
    required this.pendingChanges,
    this.lastSyncAt,
    this.lastAttemptAt,
    this.lastError,
    this.lastRejected = const <MutationRejection>[],
  });

  factory SyncState.fromJson(Map<String, dynamic> json) {
    return SyncState(
      cursor: json['cursor'] as String?,
      pendingChanges: (json['pendingChanges'] as List<dynamic>? ?? <dynamic>[])
          .map(
            (dynamic item) =>
                ChangeEnvelope.fromJson(item as Map<String, dynamic>),
          )
          .toList(growable: false),
      lastSyncAt: _tryParseDate(json['lastSyncAt'] as String?),
      lastAttemptAt: _tryParseDate(json['lastAttemptAt'] as String?),
      lastError: json['lastError'] as String?,
      lastRejected: (json['lastRejected'] as List<dynamic>? ?? <dynamic>[])
          .map(
            (dynamic item) =>
                MutationRejection.fromJson(item as Map<String, dynamic>),
          )
          .toList(growable: false),
    );
  }

  final String? cursor;
  final List<ChangeEnvelope> pendingChanges;
  final DateTime? lastSyncAt;
  final DateTime? lastAttemptAt;
  final String? lastError;
  final List<MutationRejection> lastRejected;

  static const Object _unset = Object();

  static const SyncState empty = SyncState(
    pendingChanges: <ChangeEnvelope>[],
    lastRejected: <MutationRejection>[],
  );

  SyncState copyWith({
    Object? cursor = _unset,
    List<ChangeEnvelope>? pendingChanges,
    Object? lastSyncAt = _unset,
    Object? lastAttemptAt = _unset,
    Object? lastError = _unset,
    List<MutationRejection>? lastRejected,
  }) {
    return SyncState(
      cursor: identical(cursor, _unset) ? this.cursor : cursor as String?,
      pendingChanges: pendingChanges ?? this.pendingChanges,
      lastSyncAt: identical(lastSyncAt, _unset)
          ? this.lastSyncAt
          : lastSyncAt as DateTime?,
      lastAttemptAt: identical(lastAttemptAt, _unset)
          ? this.lastAttemptAt
          : lastAttemptAt as DateTime?,
      lastError: identical(lastError, _unset)
          ? this.lastError
          : lastError as String?,
      lastRejected: lastRejected ?? this.lastRejected,
    );
  }

  Map<String, dynamic> toJson() {
    return <String, dynamic>{
      'cursor': cursor,
      'pendingChanges': pendingChanges
          .map((ChangeEnvelope change) => change.toJson())
          .toList(growable: false),
      'lastSyncAt': lastSyncAt?.toUtc().toIso8601String(),
      'lastAttemptAt': lastAttemptAt?.toUtc().toIso8601String(),
      'lastError': lastError,
      'lastRejected': lastRejected
          .map((MutationRejection rejection) => rejection.toJson())
          .toList(growable: false),
    };
  }

  static DateTime? _tryParseDate(String? raw) {
    if (raw == null || raw.isEmpty) {
      return null;
    }

    final DateTime? parsed = DateTime.tryParse(raw);
    return parsed?.toLocal();
  }
}