/**
 * Lo-Dash 2.4.1 (Custom Build) <http://lodash.com/>
 * Build: `lodash modularize modern exports="node" -o ./modern/`
 * Copyright 2012-2013 The Dojo Foundation <http://dojofoundation.org/>
 * Based on Underscore.js 1.5.2 <http://underscorejs.org/LICENSE>
 * Copyright 2009-2013 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 * Available under MIT license <http://lodash.com/license>
 */
var forEach = require('../collections/forEach'),
    forOwn = require('../objects/forOwn'),
    isArray = require('../objects/isArray'),
    isPlainObject = require('../objects/isPlainObject');

/**
 * The base implementation of `_.merge` without argument juggling or support
 * for `thisArg` binding.
 *
 * @private
 * @param {Object} object The destination object.
 * @param {Object} source The source object.
 * @param {Function} [callback] The function to customize merging properties.
 * @param {Array} [stackA=[]] Tracks traversed source objects.
 * @param {Array} [stackB=[]] Associates values with source counterparts.
 */
function baseMerge(object, source, callback, stackA, stackB) {
  (isArray(source) ? forEach : forOwn)(source, function(source, key) {
    var found,
        isArr,
        result = source,
        value = object[key];

    if (source && ((isArr = isArray(source)) || isPlainObject(source))) {
      // avoid merging previously merged cyclic sources
      var stackLength = stackA.length;
      while (stackLength--) {
        if ((found = stackA[stackLength] == source)) {
          value = stackB[stackLength];
          break;
        }
      }
      if (!found) {
        var isShallow;
        if (callback) {
          result = callback(value, source);
          if ((isShallow = typeof result != 'undefined')) {
            value = result;
          }
        }
        if (!isShallow) {
          value = isArr
            ? (isArray(value) ? value : [])
            : (isPlainObject(value) ? value : {});
        }
        // add `source` and associated `value` to the stack of traversed objects
        stackA.push(source);
        stackB.push(value);

        // recursively merge objects and arrays (susceptible to call stack limits)
        if (!isShallow) {
          baseMerge(value, source, callback, stackA, stackB);
        }
      }
    }
    else {
      if (callback) {
        result = callback(value, source);
        if (typeof result == 'undefined') {
          result = source;
        }
      }
      if (typeof result != 'undefined') {
        value = result;
      }
    }
    object[key] = value;
  });
}

module.exports = baseMerge;
