import 'dart:convert';

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

import '../models/remote_command.dart';
import '../models/venue.dart';
import '../utils/app_config.dart';

class ApiException implements Exception {
  final int statusCode;

  /// Machine-readable reason from the server, e.g. `invalid_registration_code`.
  final String? code;
  final String message;

  const ApiException(this.statusCode, this.message, {this.code});

  @override
  String toString() =>
      'HTTP $statusCode${code == null ? '' : ' ($code)'}: $message';
}

/// The device token was revoked or is invalid.
class UnauthorizedException extends ApiException {
  const UnauthorizedException({super.code, String? message})
    : super(401, message ?? 'Unauthorized');
}

/// This app is older than the backoffice accepts; it has to be updated
/// before it can sync again. The token stays valid.
class UpdateRequiredException extends ApiException {
  const UpdateRequiredException({super.code, String? message})
    : super(426, message ?? 'App update required');
}

class RateLimitedException extends ApiException {
  final Duration retryAfter;

  const RateLimitedException(this.retryAfter) : super(429, 'Rate limited');
}

class DeviceCredentials {
  final String deviceId;
  final String token;

  const DeviceCredentials({required this.deviceId, required this.token});
}

class KoolTapApiClient {
  final http.Client _client;
  final String baseUrl;

  /// Sent with every request so the backoffice can refuse an app that is too
  /// old (`426 app_update_required`).
  final String? appVersion;

  KoolTapApiClient({
    http.Client? client,
    this.baseUrl = kRemoteServerUrl,
    this.appVersion,
  }) : _client = client ?? http.Client();

  Map<String, String> get _versionHeader => {'X-App-Version': ?appVersion};

  static const _timeout = Duration(seconds: 15);
  static const _defaultRetryAfter = Duration(seconds: 60);

  Future<List<Venue>> getVenues() async {
    final response = await _client
        .get(Uri.parse('$baseUrl/venues/'), headers: _versionHeader)
        .timeout(_timeout);

    final data = _decode(response) as List<dynamic>;
    return [
      for (final venue in data) Venue.fromJson(venue as Map<String, dynamic>),
    ];
  }

  Future<DeviceCredentials> registerDevice({
    required String venueId,
    required String deviceName,
    required String registrationCode,
  }) async {
    final data =
        await _post('/devices/register', {
              'venueId': venueId,
              'name': deviceName,
              'registrationCode': registrationCode,
            })
            as Map<String, dynamic>;

    return DeviceCredentials(
      deviceId: data['deviceId'] as String,
      token: data['token'] as String,
    );
  }

  Future<SyncResponse> sync({
    required String token,
    required SyncRequest request,
  }) async {
    final data = await _post(
      '/devices/${request.deviceId}/sync',
      request.toJson(),
      token: token,
    );

    return SyncResponse.fromJson(data as Map<String, dynamic>? ?? {});
  }

  Future<void> ackCommand({
    required String token,
    required String deviceId,
    required CommandAck ack,
  }) async {
    await _post(
      '/devices/$deviceId/commands/${ack.commandId}/ack',
      ack.toJson(),
      token: token,
    );
  }

  /// Uploads a picture taken on this tablet; the server crops and stores it
  /// and returns its id, which a `product_updated` event then links.
  Future<String> uploadImage({
    required String token,
    required String deviceId,
    required List<int> bytes,
    required String filename,
  }) async {
    final request =
        http.MultipartRequest(
            'POST',
            Uri.parse('$baseUrl/devices/$deviceId/images'),
          )
          ..headers.addAll(_versionHeader)
          ..headers['Authorization'] = 'Bearer $token'
          ..files.add(
            http.MultipartFile.fromBytes('file', bytes, filename: filename),
          );
    // Uploading a photo over a slow connection takes longer than a sync
    final response = await http.Response.fromStream(
      await _client.send(request).timeout(_timeout * 4),
    );

    final data = _decode(response, authenticated: true) as Map<String, dynamic>;
    return data['imageId'] as String;
  }

  /// A product picture (public: pictures never change at their address).
  Future<List<int>> downloadImage(String imageId) async {
    final response = await _client
        .get(Uri.parse('$baseUrl/images/$imageId'), headers: _versionHeader)
        .timeout(_timeout * 2);
    if (response.statusCode != 200) {
      throw ApiException(response.statusCode, 'Image $imageId not available');
    }
    return response.bodyBytes;
  }

  Future<Object?> _post(
    String path,
    Map<String, dynamic> body, {
    String? token,
  }) async {
    final response = await _client
        .post(
          Uri.parse('$baseUrl$path'),
          headers: {
            'Content-Type': 'application/json',
            ..._versionHeader,
            if (token != null) 'Authorization': 'Bearer $token',
          },
          body: jsonEncode(body),
        )
        .timeout(_timeout);

    return _decode(response, authenticated: token != null);
  }

  /// A 401 only means the device token is no longer valid when the request
  /// used one; while pairing it means the registration code was rejected.
  Object? _decode(http.Response response, {bool authenticated = false}) {
    final status = response.statusCode;

    if (status == 401 && authenticated) {
      final error = _error(response);
      throw UnauthorizedException(code: error.code, message: error.message);
    }

    if (status == 426) {
      final error = _error(response);
      throw UpdateRequiredException(code: error.code, message: error.message);
    }

    if (status == 429) {
      final seconds = int.tryParse(response.headers['retry-after'] ?? '');
      throw RateLimitedException(
        seconds == null ? _defaultRetryAfter : Duration(seconds: seconds),
      );
    }

    if (status < 200 || status >= 300) {
      final error = _error(response);
      throw ApiException(status, error.message ?? '', code: error.code);
    }

    if (response.body.isEmpty) return null;

    return jsonDecode(response.body);
  }

  /// The server reports errors as `{"error": {"code": ..., "message": ...}}`;
  /// anything else (e.g. a proxy's HTML error page) falls back to the reason
  /// phrase.
  ({String? code, String? message}) _error(http.Response response) {
    final fallback = response.reasonPhrase;
    try {
      final error =
          (jsonDecode(response.body) as Map<String, dynamic>)['error'];
      if (error is! Map<String, dynamic>) {
        return (code: null, message: fallback);
      }

      return (
        code: error['code'] as String?,
        message: error['message'] as String? ?? fallback,
      );
    } on FormatException {
      return (code: null, message: fallback);
    } on TypeError {
      return (code: null, message: fallback);
    }
  }
}