javascript 写策略模式，商场收银打折优惠策略

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-----------------------------
  购物清单  

  方便面 : 100 x 50 = 5000 |  4000
  菊花茶 : 10 x 50 = 500 |  500
-----------------------------
  优惠使用 : 国庆1折优惠
  购物合计  4500 -> 450

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首先封装收银机类，怎么把商品设进，怎么把收银金额输出。

然后封装商品，和金额独立

然后进行收银策略编写。打折，满返针对的是最后的结果。

收银机添加设置策略接口，调用原生金额接口，调用策略接口，获得策略后金额接口

下个需求到商品的具体折扣，譬如买几送几

封装策略到商品处，商品创建的时候根据自己的名字到工厂去领取自己的“福利”

后续还想实施，组合折扣，譬如买牙膏同时买牙刷，减5块钱

架构要大改了(・-・*) ，暂时搁置 

/**
 * by JackChen 2016-3-15 19.20.01
 * 看完马士兵老师策略模式后作业
 *
 * 原文是讲解comparable接口 和 compareTo
 * 
 * 所有实现了comparable接口的类都可以用于比较。
 * 
 * 而更高级的是，我不同场景需要不同的比较时，通过定制本类的比较器，
 * 借用比较器的compareTo，得到不同的比较结果
 *
 * 已实现
 * 1. 单个物品多个数量
 * 2. 多个物品多个数量
 * 3. 多个物品结算打印
 * 4. 多个物品总金额折扣策略（几折、满返）
 * 5. 单个物品优惠策略（多少个送多少个）
 *
 * 待实现
 * 6. 单个物品 买多个送多个 跟购物物品无关
 * 7. 组合购买
 */




////////////////////////////////////////////////////////////////////////
///  收银策略类

//普通收钱
var NormalStrategy = function() {
    var self = this;
    self.type = "total";
    self.description = "没有使用优惠";
};
NormalStrategy.prototype = {};
NormalStrategy.prototype.constructor = NormalStrategy;
NormalStrategy.prototype.desc = function() {
    return this.description;
};
NormalStrategy.prototype.discount = function(money) {
    return money;
};

//折扣策略
var PrecentOffStrategy = function(description, precent) {
    var self = this;
    self.type = "total";
    self.precent = precent;
    self.description = description + (precent*10) + "折优惠";
};
PrecentOffStrategy.prototype = new NormalStrategy();
PrecentOffStrategy.prototype.constructor = PrecentOffStrategy;
PrecentOffStrategy.prototype.desc = function() {
    return this.description;
};
PrecentOffStrategy.prototype.discount = function(money) {
    return money * this.precent;
};

//满返策略
var GivebackStrategy = function(description, enough, giveback) {
    var self = this;
    self.type = "total";
    self.enough = enough;
    self.giveback = giveback;
    self.description = description + "满"+ enough + "返" + giveback + "优惠";
};
GivebackStrategy.prototype = new NormalStrategy();
GivebackStrategy.prototype.constructor = GivebackStrategy;
GivebackStrategy.prototype.desc = function() {
    return this.description;
};
GivebackStrategy.prototype.discount = function(money) {
    if (money >= this.enough) {
        money -= this.giveback;
    };
    return money;
};











////////////////////////////////////////////////////////////////////////
///  销售品种折扣工厂

var SaleItemStrategyFactory = function() {
};
SaleItemStrategyFactory.prototype = {};
SaleItemStrategyFactory.prototype.constructor = SaleItemStrategyFactory;
SaleItemStrategyFactory.prototype.getInstance = function(name) {
    var self = this;
    var strategy = null;

    switch (name) {
        case "方便面":
            strategy = new BuyMoreStrategy("特惠",4,1);
            break;
        default:
            // statements_def
            break;
    }


    return strategy;
};

//普通
var ItemNormalStrategy = function() {
    var self = this;
    self.type = "total";
    self.description = "没有优惠";
};
ItemNormalStrategy.prototype = {};
ItemNormalStrategy.prototype.constructor = ItemNormalStrategy;
ItemNormalStrategy.prototype.desc = function() {
    return this.description;
};
ItemNormalStrategy.prototype.discount = function(money) {
    return money;
};

//买几送几
var BuyMoreStrategy = function(description, buy, free) {
    var self = this;
    self.type = "total";
    self.buy = buy;
    self.free = free;
    self.description = description + "买"+ buy + "送" + free;
};
BuyMoreStrategy.prototype = new ItemNormalStrategy();
BuyMoreStrategy.prototype.constructor = BuyMoreStrategy;
BuyMoreStrategy.prototype.desc = function() {
    return this.description;
};
BuyMoreStrategy.prototype.discount = function(item) {
    var give = item.num / (this.buy + this.free);
    var left = item.num % (this.buy + this.free);
    money = (give* this.buy + left)*item.price;
    return money;
};














////////////////////////////////////////////////////////////////////////
///  销售品种

var SaleItem = function(name , price) {
    var self = this;
    self.name = name;
    self.price = price;
    self.num = 1;
    self.strategy = factory.getInstance(self.name);
};
SaleItem.prototype = {};
SaleItem.prototype.constructor = SaleItem;
SaleItem.prototype.clone = function() {
    var self = this;
    var cloneItem = new SaleItem();
    cloneItem.name = self.name;
    cloneItem.price = self.price;
    cloneItem.num = self.num;
    cloneItem.strategy = self.strategy;
    return cloneItem;
};
SaleItem.prototype.count = function() {
    return this.price * this.num;
};
SaleItem.prototype.discountProcess = function(money) {
    if (this.strategy) {
        money = this.strategy.discount(this);
    };
    return money;
};
SaleItem.prototype.discount = function() {
    return this.discountProcess(this.count());
};








////////////////////////////////////////////////////////////////////////
///  收银策略类

var CashRegister = function() {
    var self = this;
    self.totalDiscountStrategy = new NormalStrategy();
    self.arr = [];
};
CashRegister.prototype = {};
CashRegister.prototype.constructor = CashRegister;

//添加商品
CashRegister.prototype.add = function(item, num) {
    var self = this;
    if (num) {
        item.num = num;
    };
    
    self.arr.push(item);
};
//添加折扣策略
CashRegister.prototype.setTotalDiscountStrategy = function(strategy) {
    this.totalDiscountStrategy = strategy;
};

//总计金额
CashRegister.prototype.count = function() {
    var self = this;
    var totalMoney = 0;
    self.arr.forEach( function(item, index) {
        totalMoney += item.discount();
    });
    return totalMoney;
};
//折扣加入
CashRegister.prototype.discountProcess = function(money) {
    var self = this;
    if (self.totalDiscountStrategy) {
        money = self.totalDiscountStrategy.discount(money);
    };
    return money;
};
//折后金额
CashRegister.prototype.discount = function() {
    var self = this;
    var totalMoney = self.count();
    return self.discountProcess( totalMoney );
};

//结算清单
CashRegister.prototype.print = function() {
    var self = this;
    console.log('-----------------------------');
    console.log('  购物清单  ');
    console.log('');

    var totalMoney = 0;
    self.arr.forEach(function(item, index) {
        console.log("  %s : %s x %s = %s | ",item.name, item.price, item.num, item.count(),item.discount());
    });

    console.log('-----------------------------');
    console.log('  优惠使用 : ' + self.totalDiscountStrategy.desc())
    console.log('  购物合计  ' + self.count() +" -> "+ self.discount() );
    console.log('');
};













////////////////////////////////////////////////////////////////////////
///  测试类

var factory = new SaleItemStrategyFactory();

var cashRegister = new CashRegister();
cashRegister.setTotalDiscountStrategy(new PrecentOffStrategy("国庆",0.1));
// cashRegister.setTotalDiscountStrategy(new GivebackStrategy("劳动节",500,300));
// cashRegister.setTotalDiscountStrategy(new GivebackStrategy("劳动节",1000,500));


cashRegister.add(new SaleItem("方便面",100),50);
cashRegister.add(new SaleItem("菊花茶",10),50);




cashRegister.print();