import csv


def register(username, password):
    # 读取现有的用户信息
    existing_users = read_users()

    # 检查用户名是否已存在
    if username in existing_users:
        return False, "Username already exists."

    # 添加新用户信息
    new_user = {"username": username, "password": password}
    existing_users[username] = new_user

    # 将用户信息保存到CSV文件
    save_users(existing_users)

    return True, "Registration successful."


def login(username, password):
    # 读取用户信息
    existing_users = read_users()

    # 验证用户名和密码
    user = existing_users.get(username)
    if user and user["password"] == password:
        return True, "Login successful."
    return False, "Invalid credentials."


def read_users():
    # 从CSV文件中读取用户信息
    users = {}
    try:
        with open("data/users.csv", "r", newline="") as csvfile:
            reader = csv.DictReader(csvfile)
            for row in reader:
                users[row["username"]] = {"username": row["username"], "password": row["password"]}
    except FileNotFoundError:
        pass  # 如果文件不存在，说明还没有注册用户，返回一个空字典
    return users


def save_users(users):
    # 将用户信息保存到CSV文件
    with open("data/users.csv", "w", newline="") as csvfile:
        fieldnames = ["username", "password"]
        writer = csv.DictWriter(csvfile, fieldnames=fieldnames)
        writer.writeheader()
        for user in users.values():
            writer.writerow(user)

# 测试注册功能
# register("user1", "password1")
# register("user2", "password2")

# 测试登录功能
# login_success, message = login("user1", "password1")
# print(message)  # 输出：Login successful.
#
# login_success, message = login("user3", "password3")
# print(message)  # 输出：Invalid credentials.