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/**
 * Extension (not real part of the spec but nice to have for vert.x)
 * @param {object} obj native vert.x object
 * @return wrapper function that follows the promise flow.
 */
export function promisify(obj) {
  if (typeof obj === 'function') {
    return function () {
      const args = [obj].concat(Array.prototype.slice.call(arguments));
      return new Promise(function (resolve, reject) {
        args.push(function (err, res) {
          if (err) {
            reject(err);
          } else {
            resolve(res);
          }
        });
        Function.call.apply(obj, args);
      });
    }
  } else if (typeof obj === 'object') {
    return new Proxy(obj, {
      get: function (obj, prop) {
        if (typeof obj[prop] !== 'function') {
          return obj[prop];
        }

        return function () {
          let args = [obj].concat(Array.prototype.slice.call(arguments));
          return new Promise(function (resolve, reject) {
            args.push(function (res) {
              if (res.failed()) {
                reject(res.cause());
              } else {
                resolve(res.result());
              }
            });
            Function.call.apply(obj[prop], args);
          });
        };
      }
    });
  }
}