/**
 * This is just a simple version of deep copy
 * Has a lot of edge cases bug
 * If you want to use a perfect deep copy, use lodash's _.cloneDeep
 * @param {Object} source
 * @returns {Object}
 */
export function deepClone(source) {
  if (!source && typeof source !== 'object') {
    throw new Error('error arguments', 'deepClone')
  }
  const targetObj = source.constructor === Array ? [] : {}
  Object.keys(source).forEach(keys => {
    if (source[keys] && typeof source[keys] === 'object') {
      targetObj[keys] = deepClone(source[keys])
    } else {
      targetObj[keys] = source[keys]
    }
  })
  return targetObj
}

/**
 * Merges two objects, giving the last one precedence
 * @param {Object} target
 * @param {(Object|Array)} source
 * @returns {Object}
 */
export function objectMerge(target, source) {
  if (typeof target !== 'object') {
    target = {}
  }
  if (Array.isArray(source)) {
    return source.slice()
  }
  Object.keys(source).forEach(property => {
    const sourceProperty = source[property]
    if (typeof sourceProperty === 'object') {
      target[property] = objectMerge(target[property], sourceProperty)
    } else {
      target[property] = sourceProperty
    }
  })
  return target
}

/**
 * 生成uuid方法
 * @returns {string}
 */
export const createUUID = function() {
  var d = new Date().getTime()
  if (window.performance && typeof window.performance.now === 'function') {
    d += performance.now() // use high-precision timer if available
  }
  var uuid = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
    var r = (d + Math.random() * 16) % 16 | 0
    d = Math.floor(d / 16)
    return (c === 'x' ? r : (r & 0x3 | 0x8)).toString(16)
  })
  return uuid
}

/**
 * @param {Function} func
 * @param {number} wait
 * @return {*}
 */
export function throttle(func, wait, options) {
  /* options的默认值
  *  表示首次调用返回值方法时，会马上调用func；否则仅会记录当前时刻，当第二次调用的时间间隔超过wait时，才调用func。
  *  options.leading = true;
  * 表示当调用方法时，未到达wait指定的时间间隔，则启动计时器延迟调用func函数，若后续在既未达到wait指定的时间间隔和func函数又未被调用的情况下调用返回值方法，则被调用请求将被丢弃。
  *  options.trailing = true;
  * 注意：当options.trailing = false时，效果与上面的简单实现效果相同
  */
  let context, args, result
  let timeout = null
  let previous = 0
  if (!options) options = {}
  const later = function() {
    previous = options.leading === false ? 0 : Date.now()
    timeout = null
    result = func.apply(context, args)
    if (!timeout) context = args = null
  }
  return function() {
    const now = Date.now()
    if (!previous && options.leading === false) previous = now
    // 计算剩余时间
    const remaining = wait - (now - previous)
    context = this
    args = arguments
    // 当到达wait指定的时间间隔，则调用func函数
    // 精彩之处：按理来说remaining <= 0已经足够证明已经到达wait的时间间隔，但这里还考虑到假如客户端修改了系统时间则马上执行func函数。
    if (remaining <= 0 || remaining > wait) {
      // 由于setTimeout存在最小时间精度问题，因此会存在到达wait的时间间隔，但之前设置的setTimeout操作还没被执行，因此为保险起见，这里先清理setTimeout操作
      if (timeout) {
        clearTimeout(timeout)
        timeout = null
      }
      previous = now
      result = func.apply(context, args)
      if (!timeout) context = args = null
    } else if (!timeout && options.trailing !== false) {
      // options.trailing=true时，延时执行func函数
      timeout = setTimeout(later, remaining)
    }
    return result
  }
}

/**
 * @param {Function} func
 * @param {number} wait
 * @param {boolean} immediate
 * @return {*}
 */
export function debounce(func, wait, immediate) {
  let timeout, args, context, timestamp, result

  const later = function() {
    // 据上一次触发时间间隔
    const last = +new Date() - timestamp

    // 上次被包装函数被调用时间间隔 last 小于设定时间间隔 wait
    if (last < wait && last > 0) {
      timeout = setTimeout(later, wait - last)
    } else {
      timeout = null
      // 如果设定为immediate===true，因为开始边界已经调用过了此处无需调用
      if (!immediate) {
        result = func.apply(context, args)
        if (!timeout) context = args = null
      }
    }
  }

  return function(...args) {
    context = this
    timestamp = +new Date()
    const callNow = immediate && !timeout
    // 如果延时不存在，重新设定延时
    if (!timeout) timeout = setTimeout(later, wait)
    if (callNow) {
      result = func.apply(context, args)
      context = args = null
    }

    return result
  }
}