def login(username, password):
  """
  用于用户名和密码的验证
  :param username:用户名
  :param paaword:密码
  :return:True,用户验证成功；False，用户验证失败
  """
  try:
    f = open("users", "r", encoding="utf-8")
    for line in f:
      line = line.strip() # 清除换行符
      # 无参数时移除两侧空格，换行符
      # 有参数时移除两侧指定的字符
      line_list = line.split("$")
      if line_list[0] == username and line_list[1] == password:
        # print("成功")
        return True
    return False
  except IOError:
    return False


def register(username, password):
  """
  注册用户
  1、打开文件
  2、用户名$密码
  :param username:用户名
  :param password:密码
  :return:True：注册成功；
  """
  with open("users", "a", encoding="utf-8") as f:
    temp = "\n" + username + "$" + password
    f.write(temp)
    return True


def user_exist(username):
  """
  检测用户名是否存在
  :param username:要检测的用户名
  :return: True：用户名存在；False：用户名不存在
  """
  # 一行一行的去查找，如果用户名存在，return True：False
  try:
    with open("users", "r", encoding="utf-8") as f:
      for line in f:
        line = line.strip()
        line_new = line.split("$")
        if line_new[0] == username:
          return True
      return False
  except IOError:
    return False


def main():
  while True:
    print("欢迎登录xxx系统")
    arg = input("1:登录，2：注册")

    if arg == "1":
      uer = input("请输入用户名:")
      pwd = input("请输入密码:")
      if login(uer, pwd):
        print("成功")
        break
      else:
        print("失败")
    elif arg == "2":
      user = input("请输入用户名:")
      pwd = input("请输入密码:")
      is_exist = user_exist(user)
      if is_exist:
        print("用户名已经存在，注册失败")
      else:
        if register(user, pwd):
          print("注册成功")
          continue
        else:
          print("注册失败")
    else:
      print("输入错误，请重新输入")


main()