/**
* @param: orderType 表示订单类型
* @param: pay 表示用户是否已经支付定金
* @param: stock 表示当前用户普通购买的手机库存数量，交过定金的用户不受此限制
**/
var order500 = function( orderType, pay, stock ){
  if( orderType === 1 && pay === true)
     console.log('500元定金预购，得到100优惠卷');
  else
     return 'nextSuccessor'; //不知道下一个节点是谁，反正把请求往后面传递
};
var order200 = function( orderType, pay, stock){
  if( orderType === 2 && pay === true)
    console.log( '200元定金预购，得到50元优惠卷' );
  else
    return 'nextSuccessor';
};
var orderNormal = function(orderType, pay, stock){
  if(stock > 0)
    console.log('普通购买，无优惠卷');
  else
    console.log('手机库存不足');
};

var Chain = function(fn){
  this.fn = fn;
  this.successor = null;
};
Chain.prototype.setNextSuccessor = function( successor ){
  return this.successor = successor;
};
Chain.prototype.passRequest = function(){
  var ret = this.fn.apply( this, arguments );
  if( ret === 'nextSuccessor'){
    return this.successor && this.successor.passRequest.apply( this,successor, arguments );
  }
   return ret;
};

var chainOrder500 = new Chain( order500 );
var chainOrder200 = new Chain( order200 );
var chainOrderNormal = new Chain( orderNormal );

chainOrder500.setNextSuccessor( chainOrder200 );
chainOrder200.setNextSuccessor( chainOrderNormal );

chainOrder500.passRequest( 1, true, 500 ); //输出：500元定金预购，得到100优惠卷
chainOrder500.passRequest( 2, true, 500 ); //输出：200元定金预购，得到50优惠卷
chainOrder500.passRequest( 3, true, 500 ); //输出：普通购买，无优惠卷
chainOrder500.passRequest( 1, false, 0 ); //输出：手机库存不足