"""
单表替换密码 (Monoalphabetic Cipher)
实现字母表的随机替换加密
"""

import random
import string


def generate_key():
    """
    生成随机替换密钥
    返回: 字典，包含字母到替换字母的映射
    """
    alphabet = list(string.ascii_uppercase)
    shuffled = alphabet.copy()
    random.shuffle(shuffled)
    
    key = {}
    for i, char in enumerate(alphabet):
        key[char] = shuffled[i]
        key[char.lower()] = shuffled[i].lower()
    
    return key


def monoalphabetic_encrypt(text, key):
    """
    单表替换加密
    
    Args:
        text: 要加密的文本
        key: 替换密钥字典
    
    Returns:
        加密后的文本
    """
    encrypted_text = ""
    
    for char in text:
        if char in key:
            encrypted_text += key[char]
        else:
            encrypted_text += char
    
    return encrypted_text


def monoalphabetic_decrypt(text, key):
    """
    单表替换解密
    
    Args:
        text: 要解密的文本
        key: 替换密钥字典
    
    Returns:
        解密后的文本
    """
    # 创建反向密钥
    reverse_key = {v: k for k, v in key.items()}
    
    decrypted_text = ""
    
    for char in text:
        if char in reverse_key:
            decrypted_text += reverse_key[char]
        else:
            decrypted_text += char
    
    return decrypted_text


def display_key(key):
    """
    显示替换密钥表
    
    Args:
        key: 替换密钥字典
    """
    # 构建密文字母表
    plain_alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    cipher_alphabet = ''.join([key[char] for char in plain_alphabet])
    
    print("替换密钥表:")
    print(f"明文字母表: {plain_alphabet}")
    print(f"密文字母表: {cipher_alphabet}")
    print()


def main():
    """主函数 - 交互式界面"""
    print("=" * 50)
    print("单表替换密码 (Monoalphabetic Cipher)")
    print("=" * 50)
    
    # 生成密钥
    key = generate_key()
    display_key(key)
    
    while True:
        print("\n选择操作:")
        print("1. 加密")
        print("2. 解密")
        print("3. 重新生成密钥")
        print("4. 退出")
        
        choice = input("请输入选择 (1-4): ").strip()
        
        if choice == "1":
            text = input("明文: ")
            result = monoalphabetic_encrypt(text, key)
            print(f"密文: {result}")
            
        elif choice == "2":
            text = input("密文: ")
            result = monoalphabetic_decrypt(text, key)
            print(f"明文: {result}")
            
        elif choice == "3":
            key = generate_key()
            display_key(key)
            print("已重新生成密钥")
            
        elif choice == "4":
            print("再见!")
            break
            
        else:
            print("无效选择，请重新输入!")


if __name__ == "__main__":
    main()