Base Abstraction for GraphQL request

graphlql_base_service.dart

import 'package:flutter/widgets.dart';
import 'package:gql/language.dart';
import 'package:graphql_flutter/graphql_flutter.dart';
import 'package:provider/provider.dart';

enum BaseServiceRequestType { QUERY, MUTATION }

/// [T] is a return value
abstract class BaseService<T> {
  /// [context] is a navigator context, this context doesn't have
  /// capability to grab [MediaQuery] or [OverlayState]
  /// This context have to be a final member and has an [owner]
  BuildContext get context => Catcher.navigatorKey.currentContext;

  GQLClient get _gqlClient {
    final GQLClient client = Provider.of<GQLClient>(context, listen: false);

    return client;
  }

  FetchPolicy get fetchPolicy => FetchPolicy.networkOnly;

  T onPostExecute(QueryResult result) {
    if (result.hasException) {
      throw Exception(result.exception.graphqlErrors.first.message);
    }

    return null;
  }

  Future<QueryResult> _call() {
    final GraphQLClient client = _gqlClient.client;

    if (serviceType == BaseServiceRequestType.QUERY) {
      final MutationOptions options = MutationOptions(
        documentNode: parseString(query),
        variables: parameter,
        fetchPolicy: fetchPolicy,
      );

      return client.mutate(options);
    } else if (serviceType == BaseServiceRequestType.MUTATION) {
      final QueryOptions options = QueryOptions(
        documentNode: parseString(query),
        variables: parameter,
        fetchPolicy: fetchPolicy,
      );

      return client.query(options);
    }

    return null;
  }

  Future<T> fetch<T>() async {
    final QueryResult result = await _call();
    return onPostExecute(result) as T;
  }

  String get query;

  BaseServiceRequestType get serviceType;

  Map<String, dynamic> get parameter;
}