"use strict";

const isNil = require("../../is/nullOrUndefined");

const isFunction = require("../../is/function");

const hasOwnProperty = require("../../util/hasOwnProperty");

const symIterator = require("../../symbols/iterator");

const isArrayLike = require("../../is/arrayLike");

const bind = require("../../fp/bind");

const ON_INIT = '@@transducer/init';
const ON_STEP = '@@transducer/step';
const ON_REDUCED = '@@transducer/reduced';
const ON_VALUE = '@@transducer/value';
const ON_RESULT = '@@transducer/result';
const FANTASY_LAND_REDUCE = 'fantasy-land/reduce';

var _xwrap = function () {
  function XWrap(fn) {
    this.f = fn;
  }

  XWrap.prototype[ON_INIT] = function () {
    throw new Error('init not implemented on XWrap');
  };

  XWrap.prototype[ON_RESULT] = function (acc) {
    return acc;
  };

  XWrap.prototype[ON_STEP] = function (acc, x) {
    return this.f(acc, x);
  }; // @TODO construct?


  return function _xwrap(fn) {
    return new XWrap(fn);
  };
}();
/**
 * @name _reduce
 * @since 5.0.0-beta.6
 * @memberOf loop
 * @return {Function}
 */
// list aka functor


const reduce = function () {
  function _arrayReduce(xf, acc, list) {
    let idx = 0;
    const len = list.length;

    while (idx < len) {
      acc = xf[ON_STEP](acc, list[idx]);

      if (acc && acc[ON_REDUCED]) {
        acc = acc[ON_VALUE];
        break;
      }

      idx += 1;
    }

    return xf[ON_RESULT](acc);
  }

  function _iterableReduce(xf, acc, iter) {
    let step = iter.next();

    while (!step.done) {
      acc = xf[ON_STEP](acc, step.value);

      if (hasOwnProperty(acc, ON_REDUCED)) {
        acc = acc[ON_VALUE];
        break;
      }

      step = iter.next();
    }

    return xf[ON_RESULT](acc);
  }

  function _methodReduce(xf, acc, obj, methodName) {
    return xf[ON_RESULT](obj[methodName](bind(xf[ON_STEP], xf), acc));
  }

  return function _reduce(fn, acc, list) {
    if (isFunction(fn)) {
      fn = _xwrap(fn);
    }

    if (isArrayLike(list)) {
      return _arrayReduce(fn, acc, list);
    } else if (isFunction(list[FANTASY_LAND_REDUCE])) {
      return _methodReduce(fn, acc, list, FANTASY_LAND_REDUCE);
    } else if (!isNil(list[symIterator])) {
      return _iterableReduce(fn, acc, list[symIterator]());
    } else if (isFunction(list.next)) {
      return _iterableReduce(fn, acc, list);
    } else if (isFunction(list.reduce)) {
      return _methodReduce(fn, acc, list, 'reduce');
    }

    throw new TypeError('reduce: list must be array or iterable');
  };
}();

module.exports = reduce;