promises.re

open Jest;

let getData = (): Promise.promise(string) => Promise.resolved("some initial data");

type firstStepResult = {first: string};

type secondStepResult = {second: string};

let doFirstStep = (v: string) => {
  Js.log(v);
  Promise.resolved(Ok({first: "first"}));
};

let doSecondStep = (v: firstStepResult) => {
  Js.log(v);
  Promise.resolved(Ok({second: "second"}));
};

let errorOnFirstStep = (v: string) => {
  Promise.resolved(Error(v));
};

describe("Async workflow", () => {
  testPromise("Ok", () => {
    Expect.(
    
      getData()
      ->Promise.flatMap(doFirstStep)
      ->Promise.flatMapOk(doSecondStep)
      ->Promise.flatMap(x=>{
        Promise.resolved(switch x {
        | Ok(x) => expect(x) |> toEqual({second: "second"})
        | _ => fail("error")
        })
      })
      -> Promise.Js.toBsPromise
    )
  });

  testPromise("Errors", () => {
    Expect.(
      getData()
      ->Promise.flatMap(errorOnFirstStep)
      ->Promise.flatMapOk(doSecondStep)
      ->Promise.flatMap(x=> {
         Promise.resolved(
           switch (x) {
           | Error(x) => expect(x) |> toBe("some initial data")
           | _ => fail("Was not Error")
           },
         );
      })
      -> Promise.Js.toBsPromise
    )
  });

});