import * as util from 'util';

export interface IResolve<T> {
  (value?: T | Promise<T>): void;
}

export interface IReject {
  (reason?: any): void;
}

export type TDeferredStatus = 'pending' | 'fulfilled' | 'rejected';

export class Deferred<T> {
  promise: Promise<T>;
  resolve: IResolve<T>;
  reject: IReject;
  status: TDeferredStatus;
  constructor() {
    this.promise = new Promise<T>((resolve, reject) => {
      this.resolve = resolve;
      this.reject = reject;
      this.status = 'pending';
    });
  }
}

export let defer = <T>() => {
  return new Deferred<T>();
};

/**
 * Creates a new resolved promise for the provided value.
 */
export let resolvedPromise = <T>(value?: T): Promise<T> => {
  return Promise.resolve(value);
};

/**
 * Creates a new rejected promise for the provided reason.
 */
export let rejectedPromise = err => {
  return Promise.reject(err);
};

export let promisify = util.promisify;

export let map = async <T>(inputArg: T[], functionArg) => {
  let promisifedFunction = promisify(functionArg);
  let promiseArray: Promise<any>[] = [];
  let resultArray = [];
  for (let item of inputArg) {
    let promise: Promise<any> = promisifedFunction(item);
    promiseArray.push(promise);
    promise.then(x => {
      resultArray.push(x);
    });
  }
  await Promise.all(promiseArray);
  return resultArray;
};