import ApolloClient, { ApolloQueryResult, OperationVariables } from 'apollo-client';
import { DocumentNode } from 'graphql';
import ObjectHash from 'object-hash';

interface IQueryCache<T> {
    fetch: Promise<void>;
    response?: ApolloQueryResult<T>;
    error?: any;
}

const cache = new Map<string, IQueryCache<any>>();

export function gqlQuery<T, TVariables = OperationVariables>(client: ApolloClient<any>, query: DocumentNode, variables: TVariables) {
    const key = ObjectHash({query: query.definitions, variables});

    let cached: IQueryCache<T> | undefined = cache.get(key);

    if (cached) {
        if (cached.error) {
            cache.delete(key);
            throw cached.error; // error occurred
        }
        if (cached.response) {
            cache.delete(key);
            return cached.response as ApolloQueryResult<T>; // request was successful
        }
        throw cached.fetch;
    }

    cached = {
        fetch: client.query<T, TVariables>({query, variables})
            .then((resp: ApolloQueryResult<T>) => resp)
            .then((resp: ApolloQueryResult<T>) => {
                if (cached) {
                    cached.response = resp;
                }
            })
            .catch((e: any) => {
                if (cached) {
                    cached.error = e;
                }
            }),
    };

    cache.set(key, cached);

    throw cached.fetch;
}