var arrayCopy = require('./arrayCopy'),
    isArguments = require('../lang/isArguments'),
    isArray = require('../lang/isArray'),
    isLength = require('./isLength'),
    isPlainObject = require('../lang/isPlainObject'),
    isTypedArray = require('../lang/isTypedArray'),
    toPlainObject = require('../lang/toPlainObject');

/**
 * A specialized version of `baseMerge` for arrays and objects which performs
 * deep merges and tracks traversed objects enabling objects with circular
 * references to be merged.
 *
 * @private
 * @param {Object} object The destination object.
 * @param {Object} source The source object.
 * @param {string} key The key of the value to merge.
 * @param {Function} mergeFunc The function to merge values.
 * @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 {boolean} Returns `true` if the objects are equivalent, else `false`.
 */
function baseMergeDeep(object, source, key, mergeFunc, customizer, stackA, stackB) {
  var length = stackA.length,
      srcValue = source[key];

  while (length--) {
    if (stackA[length] == srcValue) {
      object[key] = stackB[length];
      return;
    }
  }
  var value = object[key],
      result = customizer ? customizer(value, srcValue, key, object, source) : undefined,
      isCommon = typeof result == 'undefined';

  if (isCommon) {
    result = srcValue;
    if (isLength(srcValue.length) && (isArray(srcValue) || isTypedArray(srcValue))) {
      result = isArray(value)
        ? value
        : (value ? arrayCopy(value) : []);
    }
    else if (isPlainObject(srcValue) || isArguments(srcValue)) {
      result = isArguments(value)
        ? toPlainObject(value)
        : (isPlainObject(value) ? value : {});
    }
    else {
      isCommon = false;
    }
  }
  // Add the source value to the stack of traversed objects and associate
  // it with its merged value.
  stackA.push(srcValue);
  stackB.push(result);

  if (isCommon) {
    // Recursively merge objects and arrays (susceptible to call stack limits).
    object[key] = mergeFunc(result, srcValue, customizer, stackA, stackB);
  } else if (result === result ? result !== value : value === value) {
    object[key] = result;
  }
}

module.exports = baseMergeDeep;
