ramda-adjunct/es/reduceRightP.js

Ramda Adjunct is the most popular and most comprehensive set of utilities for use with Ramda, providing a variety of useful, well tested functions with excellent documentation.

function _slicedToArray(arr, i) { return _arrayWithHoles(arr) || _iterableToArrayLimit(arr, i) || _nonIterableRest(); }

function _nonIterableRest() { throw new TypeError("Invalid attempt to destructure non-iterable instance"); }

function _iterableToArrayLimit(arr, i) { var _arr = []; var _n = true; var _d = false; var _e = undefined; try { for (var _i = arr[Symbol.iterator](), _s; !(_n = (_s = _i.next()).done); _n = true) { _arr.push(_s.value); if (i && _arr.length === i) break; } } catch (err) { _d = true; _e = err; } finally { try { if (!_n && _i["return"] != null) _i["return"](); } finally { if (_d) throw _e; } } return _arr; }

function _arrayWithHoles(arr) { if (Array.isArray(arr)) return arr; }

import { curryN, pipe, equals, reduceRight, length, concat } from 'ramda';
import isUndefined from './isUndefined';
import resolveP from './resolveP';
import allP from './allP'; // in older ramda versions the order of the arguments is flipped

var flipArgs = pipe(reduceRight(concat, ''), equals('ba'))(['a', 'b']);
/* eslint-disable max-len */

/**
 * Given an `Iterable`(arrays are `Iterable`), or a promise of an `Iterable`,
 * which produces promises (or a mix of promises and values),
 * iterate over all the values in the `Iterable` into an array and
 * reduce the array to a value using the given iterator function.
 *
 * Similar to {@link RA.reduceP|reduceP} except moves through the input list from the right to the left.
 * The iterator function receives two values: (value, acc),
 * while the arguments' order of reduceP's iterator function is (acc, value).
 *
 * @func reduceRightP
 * @memberOf RA
 * @since {@link https://char0n.github.io/ramda-adjunct/1.13.0|v1.13.0}
 * @category List
 * @typedef MaybePromise = Promise.<*> | *
 * @sig ((MaybePromise b, Promise a) -> Promise a) -> MaybePromise a -> MaybePromise [MaybePromise b] -> Promise a
 * @param {Function} fn The iterator function. Receives two values, the current element from the list and the accumulator
 * @param {*|Promise.<*>} acc The accumulator value
 * @param {Array.<*>|Promise.<Array<*|Promise.<*>>>} list The list to iterate over
 * @return {Promise} The final, accumulated value
 * @see {@link RA.reduceP|reduceP}, {@link http://bluebirdjs.com/docs/api/promise.reduce.html|bluebird.reduce}
 * @example
 *
 * RA.reduceRightP(
 *   (fileName, total) => fs
 *     .readFileAsync(fileName, 'utf8')
 *     .then(contents => total + parseInt(contents, 10)),
 *   0,
 *   ['file1.txt', 'file2.txt', 'file3.txt']
 * ); // => Promise(10)
 *
 * RA.reduceRightP(
 *   (fileName, total) => fs
 *     .readFileAsync(fileName, 'utf8')
 *     .then(contents => total + parseInt(contents, 10)),
 *   Promise.resolve(0),
 *   ['file1.txt', 'file2.txt', 'file3.txt']
 * ); // => Promise(10)
 *
 * RA.reduceRightP(
 *   (fileName, total) => fs
 *     .readFileAsync(fileName, 'utf8')
 *     .then(contents => total + parseInt(contents, 10)),
 *   0,
 *   [Promise.resolve('file1.txt'), 'file2.txt', 'file3.txt']
 * ); // => Promise(10)
 *
 * RA.reduceRightP(
 *   (fileName, total) => fs
 *     .readFileAsync(fileName, 'utf8')
 *     .then(contents => total + parseInt(contents, 10)),
 *   0,
 *   Promise.resolve([Promise.resolve('file1.txt'), 'file2.txt', 'file3.txt'])
 * ); // => Promise(10)
 *
 */

/* esline-enable max-len */

var reduceRightP = curryN(3, function (fn, acc, list) {
  return resolveP(list).then(function (iterable) {
    var listLength = length(iterable);

    if (listLength === 0) {
      return acc;
    }

    var reducer = reduceRight(function (arg1, arg2) {
      var accP;
      var currentValueP;

      if (flipArgs) {
        accP = arg1;
        currentValueP = arg2;
      } else {
        accP = arg2;
        currentValueP = arg1;
      }

      return accP.then(function (previousValue) {
        return allP([previousValue, currentValueP]);
      }).then(function (_ref) {
        var _ref2 = _slicedToArray(_ref, 2),
            previousValue = _ref2[0],
            currentValue = _ref2[1];

        if (isUndefined(previousValue) && listLength === 1) {
          return currentValue;
        }

        return fn(currentValue, previousValue);
      });
    });
    return reducer(resolveP(acc), iterable);
  });
});
export default reduceRightP;