/**
 * Copyright (c) 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule insertIntoList
 * @format
 * @flow
 */

'use strict';

import type { List } from 'immutable';

/**
 * Maintain persistence for target list when appending and prepending.
 */
function insertIntoList<T>(targetList: List<T>, toInsert: List<T>, offset: number): List<T> {
  if (offset === targetList.count()) {
    toInsert.forEach(c => {
      targetList = targetList.push(c);
    });
  } else if (offset === 0) {
    toInsert.reverse().forEach(c => {
      targetList = targetList.unshift(c);
    });
  } else {
    var head = targetList.slice(0, offset);
    var tail = targetList.slice(offset);
    targetList = head.concat(toInsert, tail).toList();
  }
  return targetList;
}

module.exports = insertIntoList;