/**
 * Checks if `value` is an empty object, collection, map, or set.
 *
 * Objects are considered empty if they have no own enumerable string keyed
 * properties.
 *
 * Array-like values such as `arguments` objects, arrays, buffers, strings, or
 * jQuery-like collections are considered empty if they have a `length` of `0`.
 * Similarly, maps and sets are considered empty if they have a `size` of `0`.
 *
 * @since 0.1.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is empty, else `false`.
 * @example
 *
 * isEmpty(null)
 * // => true
 *
 * isEmpty(true)
 * // => true
 *
 * isEmpty(1)
 * // => true
 *
 * isEmpty([1, 2, 3])
 * // => false
 *
 * isEmpty('abc')
 * // => false
 *
 * isEmpty({ 'a': 1 })
 * // => false
 */
function isEmpty(value) {
  if (value == null) {
    return true
  }
  //类数组、str、buffer、arguments
  if (isArrayLike(value) &&
      (Array.isArray(value) || typeof value === 'string' || typeof value.splice === 'function' ||
        isBuffer(value) || isTypedArray(value) || isArguments(value))) {
    return !value.length
  }
  //set,map 
  const tag = getTag(value)
  if (tag == '[object Map]' || tag == '[object Set]') {
    return !value.size
  }
  //对象
  if (isPrototype(value)) {
    return !Object.keys(value).length
  }
  for (const key in value) {
    if (hasOwnProperty.call(value, key)) {
      return false
    }
  }
  return true
}

export default isEmpty

const toString = Object.prototype.toString

/**
 * Gets the `toStringTag` of `value`.
 *
 * @private
 * @param {*} value The value to query.
 * @returns {string} Returns the `toStringTag`.
 */
function getTag(value) {
  if (value == null) {
    return value === undefined ? '[object Undefined]' : '[object Null]'
  }
  return toString.call(value) //这个写法，值得学习
}

export default getTag

/** Used for built-in method references. */
const objectProto = Object.prototype

/**
 * Checks if `value` is likely a prototype object.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a prototype, else `false`.
 */
function isPrototype(value) {
  const Ctor = value && value.constructor
  const proto = (typeof Ctor === 'function' && Ctor.prototype) || objectProto

  return value === proto
}

export default isPrototype

function isArguments(value) {
  return isObjectLike(value) && getTag(value) == '[object Arguments]'
}

export default isArguments