var _curryN = require('./internal/_curryN');
var _reduce = require('./internal/_reduce');
var _reduced = require('./internal/_reduced');


/**
 * Like [`reduce`](#reduce), `reduceWhile` returns a single item by iterating
 * through the list, successively calling the iterator function. `reduceWhile`
 * also takes a predicate that is evaluated before each step. If the predicate
 * returns `false`, it "short-circuits" the iteration and returns the current
 * value of the accumulator.
 *
 * @func
 * @memberOf R
 * @since v0.22.0
 * @category List
 * @sig ((a, b) -> Boolean) -> ((a, b) -> a) -> a -> [b] -> a
 * @param {Function} pred The predicate. It is passed the accumulator and the
 *        current element.
 * @param {Function} fn The iterator function. Receives two values, the
 *        accumulator and the current element.
 * @param {*} a The accumulator value.
 * @param {Array} list The list to iterate over.
 * @return {*} The final, accumulated value.
 * @see R.reduce, R.reduced
 * @example
 *
 *      var isOdd = (acc, x) => x % 2 === 1;
 *      var xs = [1, 3, 5, 60, 777, 800];
 *      R.reduceWhile(isOdd, R.add, 0, xs); //=> 9
 *
 *      var ys = [2, 4, 6]
 *      R.reduceWhile(isOdd, R.add, 111, ys); //=> 111
 */
module.exports = _curryN(4, [], function _reduceWhile(pred, fn, a, list) {
  return _reduce(function(acc, x) {
    return pred(acc, x) ? fn(acc, x) : _reduced(acc);
  }, a, list);
});