export class BusyPromise {

  /**
   * Promise wrapper that calls pre and post methods. Can be used to auto increment and decrement a
   * counter, for example, or to indicate when busy and unbusy.
   * @param opts {Object}
   * @param [opts.pre] {Function} Function to execute before calling function
   * @param [opts.onResolve] {Function} Function to execute after function resolves
   * @param [opts.onReject] {Function} Function to execute if function rejects
   * @param fn {function} Same as function in new Promise(fn)
   */
  constructor (opts, fn) {
    this.opts = opts;
    this.opts.pre && this.opts.pre();
    this.p = new Promise((resolve, reject) => {
      fn((data) => {
        this.opts.onResolve && this.opts.onResolve();
        resolve(data);
      }, (err) => {
        this.opts.onReject && this.opts.onReject(err);
        reject(err);
      });
    });
  }

  then (onResolve, onReject) {
    return this.p.then(onResolve, onReject);
  }

  catch (onReject) {
    return this.p.catch(onReject);
  }
}