import 'dart:convert';
import 'dart:math';

import 'package:http/http.dart' as http;
import 'package:shared_preferences/shared_preferences.dart';

class ApprovalTaskItem {
  const ApprovalTaskItem({
    required this.id,
    required this.name,
    required this.createdAt,
    required this.leaveRequest,
  });

  final String id;
  final String name;
  final DateTime createdAt;
  final ApprovalLeaveRequest leaveRequest;

  factory ApprovalTaskItem.fromJson(Map<String, Object?> json) =>
      ApprovalTaskItem(
        id: json['id']! as String,
        name: json['name']! as String,
        createdAt: DateTime.parse(json['createdAt']! as String),
        leaveRequest: ApprovalLeaveRequest.fromJson(
          Map<String, Object?>.from(json['leaveRequest']! as Map),
        ),
      );
}

class ApprovalLeaveRequest {
  const ApprovalLeaveRequest({
    required this.id,
    required this.type,
    required this.startsAt,
    required this.endsAt,
    required this.reason,
    required this.status,
    required this.version,
  });

  final String id;
  final String type;
  final DateTime startsAt;
  final DateTime endsAt;
  final String reason;
  final String status;
  final int version;

  factory ApprovalLeaveRequest.fromJson(Map<String, Object?> json) =>
      ApprovalLeaveRequest(
        id: json['id']! as String,
        type: json['type']! as String,
        startsAt: DateTime.parse(json['startsAt']! as String),
        endsAt: DateTime.parse(json['endsAt']! as String),
        reason: json['reason']! as String,
        status: json['status']! as String,
        version: json['version']! as int,
      );
}

class ApprovalTaskException implements Exception {
  const ApprovalTaskException(this.message);
  final String message;
  @override
  String toString() => message;
}

class ApprovalTaskRepository {
  ApprovalTaskRepository({
    http.Client? client,
    this.baseUrl = const String.fromEnvironment(
      'AIOA_API_BASE_URL',
      defaultValue: 'http://127.0.0.1:8080/api/v1',
    ),
    this.accessToken = const String.fromEnvironment('AIOA_ACCESS_TOKEN'),
  }) : _client = client ?? http.Client();

  final http.Client _client;
  final String baseUrl;
  final String accessToken;

  Future<List<ApprovalTaskItem>> list() async {
    final response = await _client.get(
      Uri.parse('$baseUrl/approval-tasks'),
      headers: _headers,
    );
    _requireSuccess(response);
    return (jsonDecode(response.body) as List)
        .map(
          (item) =>
              ApprovalTaskItem.fromJson(Map<String, Object?>.from(item as Map)),
        )
        .toList();
  }

  Future<void> decide({
    required ApprovalTaskItem task,
    required bool approved,
    String? comment,
  }) async {
    final action = approved ? 'approve' : 'reject';
    final payload = jsonEncode({
      'version': task.leaveRequest.version,
      if (comment != null && comment.trim().isNotEmpty)
        'comment': comment.trim(),
    });
    final preferences = await SharedPreferences.getInstance();
    final storageKey = 'approval.pending.${task.id}.$action';
    final existing = preferences.getString(storageKey);
    final pending = existing == null ? null : _decodePending(existing);
    final idempotencyKey = pending?.payload == payload
        ? pending!.key
        : _newKey(action);
    await preferences.setString(
      storageKey,
      jsonEncode({'key': idempotencyKey, 'payload': payload}),
    );

    late http.Response response;
    try {
      response = await _client.post(
        Uri.parse('$baseUrl/approval-tasks/${task.id}/$action'),
        headers: {
          ..._headers,
          'Content-Type': 'application/json',
          'Idempotency-Key': idempotencyKey,
        },
        body: payload,
      );
    } catch (_) {
      throw const ApprovalTaskException('网络不可用，审批请求已保存，可安全重试');
    }
    if (response.statusCode < 200 || response.statusCode >= 300) {
      if (response.statusCode < 500 && response.statusCode != 401) {
        await preferences.remove(storageKey);
      }
      _requireSuccess(response);
    }
    await preferences.remove(storageKey);
  }

  Map<String, String> get _headers => {
    'Accept': 'application/json',
    if (accessToken.isNotEmpty) 'Authorization': 'Bearer $accessToken',
  };

  void _requireSuccess(http.Response response) {
    if (response.statusCode >= 200 && response.statusCode < 300) return;
    String? message;
    try {
      message =
          (jsonDecode(response.body) as Map<String, Object?>)['detail']
              as String?;
    } catch (_) {}
    throw ApprovalTaskException(message ?? '待办请求失败（${response.statusCode}）');
  }

  _PendingApproval? _decodePending(String encoded) {
    try {
      final json = jsonDecode(encoded) as Map<String, Object?>;
      return _PendingApproval(
        json['key']! as String,
        json['payload']! as String,
      );
    } catch (_) {
      return null;
    }
  }

  String _newKey(String action) {
    final random = Random.secure();
    final entropy = List.generate(
      12,
      (_) => random.nextInt(256).toRadixString(16).padLeft(2, '0'),
    ).join();
    return 'approval-$action-${DateTime.now().microsecondsSinceEpoch}-$entropy';
  }
}

class _PendingApproval {
  const _PendingApproval(this.key, this.payload);
  final String key;
  final String payload;
}