import 'dart:async';
import 'dart:convert';

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

import '../../domain/entities/pos_session.dart';

/// A sign-in that did not produce a session.
///
/// Carries a message written for the person at the counter, not a status code.
/// [isCredentialFailure] separates "you typed the wrong password" from "the
/// shop's internet is down", because the first is the operator's problem to
/// fix and the second is not.
class AuthApiException implements Exception {
  const AuthApiException(
    this.message, {
    this.isCredentialFailure = false,
    this.statusCode,
  });

  final String message;
  final bool isCredentialFailure;
  final int? statusCode;

  @override
  String toString() => message;
}

/// Signs the terminal in against the back office.
///
/// ```
/// POST {base}/login
/// Content-Type: application/json
///
/// { "authname": …, "password": …, "device_id": …, "configid": 1 }
/// ```
///
/// answering
///
/// ```json
/// { "code": 200, "status": true, "message": "Login successful",
///   "details": { "token": …, "role": "Supervisor", … } }
/// ```
///
/// The envelope is checked rather than the HTTP status alone: this API answers
/// `200` with `status: false` for a rejected credential, so trusting the
/// status code would sign a terminal in on a failed login.
class PosAuthApi {
  PosAuthApi({
    required this.baseUrl,
    this.configId = 1,
    http.Client? client,
  }) : _client = client ?? http.Client();

  /// Same base as the catalogue and order endpoints, e.g.
  /// `https://fiesta.nearle.app/live/api/v1/pos`.
  final String baseUrl;

  /// Which back-office configuration this terminal belongs to.
  final int configId;

  final http.Client _client;

  static const Duration _timeout = Duration(seconds: 20);

  Future<PosSession> login({
    required String authname,
    required String password,
    required String deviceId,
  }) async {
    if (baseUrl.isEmpty) {
      throw const AuthApiException(
        'No back-office URL is configured for this terminal. Set one in '
        'Settings → Connectivity & sync → Configure.',
      );
    }

    final uri = Uri.parse('${baseUrl.replaceAll(RegExp(r'/+$'), '')}/login');

    http.Response response;
    try {
      response = await _client
          .post(
            uri,
            headers: const {
              'content-type': 'application/json',
              'accept': 'application/json',
            },
            body: jsonEncode({
              'authname': authname.trim(),
              'password': password,
              // This device's own identity, minted on first run. Two terminals
              // must never sign in as the same device — the back office keys
              // sessions on it.
              'device_id': deviceId,
              'configid': configId,
            }),
          )
          .timeout(_timeout);
    } on TimeoutException {
      throw const AuthApiException(
        'The back office did not answer in time. Check the connection and '
        'try again.',
      );
    } on http.ClientException {
      // DNS failure, refused connection, dropped socket — the shop's line
      // rather than the operator's credentials.
      throw const AuthApiException(
        'Could not reach the back office. Check this terminal\'s internet '
        'connection.',
      );
    } on Exception catch (e) {
      throw AuthApiException('Could not reach the back office: $e');
    }

    Map<String, Object?> body;
    try {
      body = jsonDecode(response.body) as Map<String, Object?>;
    } on Object {
      throw AuthApiException(
        'The back office answered with something this terminal could not '
        'read (${response.statusCode}).',
        statusCode: response.statusCode,
      );
    }

    final ok = body['status'] == true && response.statusCode < 300;

    if (!ok) {
      final raw = body['message'];
      final message = raw is String ? raw.trim() : '';
      const rejectedCodes = {400, 401, 403, 422};

      throw AuthApiException(
        // The server's own wording, when it gave one. It knows whether the
        // account is disabled, the device is unregistered or the password is
        // simply wrong, and a generic message would throw that away.
        message.isEmpty ? 'Sign-in failed (${response.statusCode}).' : message,
        isCredentialFailure: rejectedCodes.contains(response.statusCode),
        statusCode: response.statusCode,
      );
    }

    final details = body['details'];
    if (details is! Map<String, Object?>) {
      throw const AuthApiException(
        'The back office accepted the sign-in but sent no session back.',
      );
    }

    final session = PosSession.fromDetails(details, authname: authname.trim());

    if (session.token.isEmpty) {
      throw const AuthApiException(
        'The back office accepted the sign-in but issued no token.',
      );
    }

    return session;
  }

  void dispose() => _client.close();
}