用函数完成登录注册以及购物车的功能.  难度系数一般
# 要求:
# 1, 启动程序, 用户可选择四个选项: 登录, 注册, 购物, 退出.
# 2, 用户注册, 用户名不能重复, 注册成功之后, 用户名密码记录到文件中.
# 3, 用户登录, 用户名密码从文件中读取，进行三次验证, 验证不成功则退出整个程序.
# 4, 用户登录成功之后才能选择购物功能进行购物, 购物功能( 就是将购物车封装到购物的 函数中).
# 5, 退出则是退出整个程序.
# 欢迎计入购物系统:
# 1. 登录
# 2. 注册
# 3. 购物
# 4. 退出





goods = [
    {"name": "电脑", "price": 1999},
    {"name": "鼠标", "price": 10},
    {"name": "游艇", "price": 20},
    {"name": "美女", "price": 998},
]

shopping_car = []
shopp_dic = {}
flag = True
def one():
    '''
    打印导航
    :return:
    '''
    print('''欢迎进入老男孩购物系统:
1.登录
2.注册
3.购物
4.退出
    ''')

def register():
    '''
    注册函数
    :return:
    '''
    while 1:
        username = input('请输入用户名:')
        password = input('请输入密码:')
        with open('user','r+',encoding='utf-8') as f:
            for line in f:
                new_line = line.split('&&')
                if username == new_line[0]:
                    print('用户名已存在,请重新输入')
                    break
            else:
                f.write('\n'+username+'&&'+password)
                print('注册成功')
                break

def login():
    '''
    登录函数
    :return:
    '''
    global flag
    count = 1
    while count <=3:
        username = input('请输入用户名:')
        password = input('请输入密码:')
        with open('user','r',encoding='utf-8') as f:
            for line in f:
                new_line = line.strip().split('&&')
                if username == new_line[0] and password == new_line[1]:
                    print('登录成功!')
                    flag = False
                    break
            else:
                print('用户名或密码错误,请重新输入,还有%s次机会' % (3-count))
                count += 1
                continue
            break


def shopping():
    '''
    购物函数
    :return:
    '''
    if flag == False:      #判断有没有登录
        while True:
            money = input('请输入存款:').strip()
            if 0 < int(money) and money.isdigit():  # 判断输入的金额是否大于0,是否是数字
                for dic in goods:
                    print(goods.index(dic) + 1, dic['name'], dic['price'])  # 打印所有商品
                while True:
                    choice = input('请输入要选择的商品序号:').strip()
                    if 0 < int(choice) <= len(goods) and choice.isdigit():
                        for shopp_dic in shopping_car:  # shopp_dic是shopping_car列表中的每一个字典
                            if goods[int(choice) - 1]['name'] == shopp_dic['name']:
                                shopp_dic['num'] += 1  # 如果选择的商品名字跟字典中的商品名字是一样的,则该商品的数量+1
                                break
                        else:  # 如果选择的商品没有在购物车,则加入购物车,
                            shopp_dic = {}
                            shopp_dic['name'] = goods[int(choice) - 1]['name']
                            shopp_dic['price'] = goods[int(choice) - 1]['price']
                            shopp_dic['num'] = 1  # 第一次加入商品初始数量为1
                            shopping_car.append(shopp_dic)
                        choice2 = input('是否继续选择Y继续,N结算:').strip()
                        if choice2.upper() == 'Y':  # 选择继续购买
                            for dic in goods:
                                print(goods.index(dic) + 1, dic['name'], dic['price'])  # 打印所有商品
                            continue
                        else:
                            for shopp_dic in shopping_car:
                                print('您已选择以下商品:')
                                print(shopp_dic)  # 打印已加购物车的商品
                            if int(money) > shopp_dic['price'] * shopp_dic['num']:  # 如果输入的总钱数大于商品总金额,告知共花费多少,剩余多少
                                surplus = int(money) - shopp_dic['price'] * shopp_dic['num']
                                print('共花费%s元,还剩%s元' % (shopp_dic['price'] * shopp_dic['num'], surplus))
                            else:  # 总金额不足
                                owe = shopp_dic['price'] * shopp_dic['num'] - int(money)
                                print('余额不足,还缺%s元' % owe)
                        break
                    else:
                        print('输入有误,请重新输入')
            else:  # 输入的数字小于0并且或者不是数字的话,重新输入
                print('输入有误,请重新输入')
            break
    else:     #没有登录的话执行登录函数
        print('您还没有登录,请先登录!')
        login()


def main():
    while True:
        one()
        choice = input('请输入选项:')
        if choice == '1':
            login()
            continue
        elif choice == '2':
            register()
        elif choice == '3':
            shopping()
        elif choice == '4':
            break
        else:
            print('输入有误,请重新输入')
        break
main()