var arrayEach = require('./arrayEach'),
    baseMergeDeep = require('./baseMergeDeep'),
    getSymbols = require('./getSymbols'),
    isArray = require('../lang/isArray'),
    isLength = require('./isLength'),
    isObject = require('../lang/isObject'),
    isObjectLike = require('./isObjectLike'),
    isTypedArray = require('../lang/isTypedArray'),
    keys = require('../object/keys');

/** Used for native method references. */
var arrayProto = Array.prototype;

/** Native method references. */
var push = arrayProto.push;

/**
 * The base implementation of `_.merge` without support for argument juggling,
 * multiple sources, and `this` binding `customizer` functions.
 *
 * @private
 * @param {Object} object The destination object.
 * @param {Object} source The source object.
 * @param {Function} [customizer] The function to customize merging properties.
 * @param {Array} [stackA=[]] Tracks traversed source objects.
 * @param {Array} [stackB=[]] Associates values with source counterparts.
 * @returns {Object} Returns `object`.
 */
function baseMerge(object, source, customizer, stackA, stackB) {
  if (!isObject(object)) {
    return object;
  }
  var isSrcArr = isLength(source.length) && (isArray(source) || isTypedArray(source));
  if (!isSrcArr) {
    var props = keys(source);
    push.apply(props, getSymbols(source));
  }
  arrayEach(props || source, function(srcValue, key) {
    if (props) {
      key = srcValue;
      srcValue = source[key];
    }
    if (isObjectLike(srcValue)) {
      stackA || (stackA = []);
      stackB || (stackB = []);
      baseMergeDeep(object, source, key, baseMerge, customizer, stackA, stackB);
    }
    else {
      var value = object[key],
          result = customizer ? customizer(value, srcValue, key, object, source) : undefined,
          isCommon = result === undefined;

      if (isCommon) {
        result = srcValue;
      }
      if ((isSrcArr || result !== undefined) &&
          (isCommon || (result === result ? (result !== value) : (value === value)))) {
        object[key] = result;
      }
    }
  });
  return object;
}

module.exports = baseMerge;
