withCastingOutput

withCastingOutput.test.ts

import { withCastingOutput } from './withCastingOutput';

describe('withCastingOutput', () => {
  it('should be able to wrap a function and add output casting to it', async () => {
    const startFromTheBottom = ({ bottom }: { bottom: boolean }) => ({
      started: `started from the ${bottom ? 'bottom' : 'top'}`,
      bottom,
    });
    const castToHere = ({ started, bottom }: { started: string; bottom?: boolean }) =>
      `${started}${bottom ? ", now we're here" : " and we're still here"}`;
    const startAndGetHere = withCastingOutput(startFromTheBottom, castToHere);
    expect(await startAndGetHere({ bottom: true })).toEqual("started from the bottom, now we're here");
    expect(await startAndGetHere({ bottom: false })).toEqual("started from the top and we're still here");
  });
});

withCastingOutput.ts

export const withCastingOutput = <
  Input extends Parameters<Logic>[0],
  OutputIn extends ReturnType<Logic>,
  Logic extends (input: any) => any,
  OutputOut extends ReturnType<Cast>,
  Cast extends (input: OutputIn) => any
>(
  logic: Logic,
  cast: Cast,
) => {
  return async (input: Input): Promise<OutputOut> => {
    const outputIn = await logic(input);
    const outputOut = await cast(outputIn);
    return outputOut;
  };
};