// Api.res

type gqlResponse = {
  data: option<Json.t>,
  errors: option<Json.t>,
}

%%private(
  @module("./api/fetchBackoffice.ts")
  external fetch: (~query: string, ~variables: 'variables) => Promise.t<gqlResponse> = "default"
)

@@uncurried.swap

module MakeRequest = (
  Query: {
    module Raw: {
      type t
    }
    type t
    type t_variables
    let query: string
    let unsafe_fromJson: (. Json.t) => Raw.t
  },
) => {
  let toTask = (. ~variables: Query.t_variables): Task.t<Query.Raw.t, string> => {
    Task.make((~resolve, ~reject) => {
      fetch(~query=Query.query, ~variables)
      ->Promise.thenResolve(response => {
        switch response {
        | {errors: Some(errors)} => reject(errors->Json.stringifyAny->Option.getExn)
        | {errors: None, data: None} => reject("Response data is empty.")
        | {errors: None, data: Some(data)} => resolve(data->Query.unsafe_fromJson)
        }
      })
      ->Promise.catch(exn => {
        exn->Exn.asJsExn->Option.flatMap(Exn.message)->Option.getExn->reject
        Promise.resolve()
      })
      ->ignore
      None
    })
  }
}

// Foo.res
%graphql(`
   query Query($registrationNumber: String!){
      carInfo(registrationNumber: $registrationNumber) {
        engineType
        modelYear
        vehicleMake
        model
      }
    }
  `)

module Request = Api.MakeRequest(Query)

Request.toTask(~variables=...)