apolloQueryWrapper.ts

type QueryLoading = {
    status: 'LOADING'
}

type QueryError = {
    status: 'ERROR'
    error: Error
}

type QuerySuccess<SuccessType> = {
    status: 'SUCCESS'
    data: SuccessType
}

type ApolloUseQueryResult<SuccessType> = QueryLoading | QueryError | QuerySuccess<SuccessType>

// These are the parts of the useQuery result we want to wrap up, converting data | error | loading => result
interface WrappableApolloQuery {
    data: any,
    error?: Error,
    loading: boolean
}

// Apollo's useQuery returns three independent variables to track loading, error, and data. In our usage
// no two of those variables should never be accessed at the same time. This wrapper replaces them with
// a single variable "result" of ApolloUseQueryResult type.
function wrapApolloResult<ResultType extends 
        WrappableApolloQuery>(queryResult: ResultType): 
            Omit<ResultType, 'data' | 'loading' | 'error'> & 
            { result: ApolloUseQueryResult<NonNullable<ResultType["data"]>> } {
    const { loading, error, data } = queryResult

    if (loading) {
        return {
            ...queryResult,
            result: {
                    status: 'LOADING',
            }
        }
    }

    if (error) {
        return {
            ...queryResult,
            result: {
                status: 'ERROR',
                error: error,
            }
        }
    }

    if (data) {
        return {
            ...queryResult,
            result: {
                status: 'SUCCESS',
                data,
            }
        }
    }

    return {
        ...queryResult,
        result: {
            status: 'ERROR',
            error: new Error('UNEXPECTED APOLLO BEHAVIOR, NO DATA'),
        }
    }
}

export {
    wrapApolloResult,
}

export type {
    ApolloUseQueryResult,
}