let hasOwn = Object.prototype.hasOwnProperty

let toString = Object.prototype.toString

let class2type = {}

let type = function (obj) {
  return obj === null ? String(obj) : class2type[ toString.call(obj) ] || 'object'
}

let isWindow = function (obj) {
  return obj && typeof obj === 'object' && 'setInterval' in obj
}

/**
 * 判断是否是纯对象
 */
let isPlainObject = function (obj) {
  if (!obj || type(obj) !== 'object' || obj.nodeType || isWindow(obj)) {
    return false
  }
  if (obj.constructor && !hasOwn.call(obj, 'constructor') && !hasOwn.call(obj.constructor.prototype, 'isPrototypeOf')) {
    return false
  }
  var key
  for (key in obj) {}
  return key === undefined || hasOwn.call(obj, key)
}

/**
 * 判断是否是纯函数
 */
let isFunction = function (obj) {
  return type(obj) === 'function'
}

/**
 * 判断是否是纯数组
 */
let isArray = Array.isArray || function (obj) {
  return type(obj) === 'array'
}

/**
 * 对象的深copy
 * 参数1： 布尔值 可以省略 判断是否深度拷贝，默认false
 * example extend(false, {a: {name: '张三'}}, {b: {name: '李四'}})
 */
export default function extend () {
  let options
  let name
  let src
  let copy
  let copyIsArray
  let clone
  let target = arguments[0] || {}
  let i = 1
  let length = arguments.length
  let deep = false
  if (typeof target === 'boolean') {
    deep = target
    target = arguments[1] || {}
    i = 2
  }
  if (typeof target !== 'object' && !isFunction(target)) {
    target = {}
  }
  if (length === i) {
    target = this
    --i
  }
  for (; i < length; i++) {
    if ((options = arguments[ i ]) !== null) {
      for (name in options) {
        src = target[name]
        copy = options[name]
        if (target === copy) {
          continue
        }
        if (deep && copy && (isPlainObject(copy) || (copyIsArray = isArray(copy)))) {
          if (copyIsArray) {
            copyIsArray = false
            clone = src && isArray(src) ? src : []
          } else {
            clone = src && isPlainObject(src) ? src : {}
          }
          target[name] = extend(deep, clone, copy)
        } else if (copy !== undefined) {
          target[name] = copy
        }
      }
    }
  }
  return target
}