import string


def _process_vigenere_char(char, key_char, mode):
    if not char.isalpha():
        return char

    start = ord('A') if char.isupper() else ord('a')
    shift = ord(key_char) - ord('A')

    if mode == "encrypt":
        processed_char_code = (ord(char) - start + shift) % 26 + start
    elif mode == "decrypt":
        processed_char_code = (ord(char) - start - shift) % 26 + start
    else:
        raise ValueError("无效的模式，必须是 'encrypt' 或 'decrypt'")

    return chr(processed_char_code)


def vigenere_encrypt(plaintext, key):
    """
    维吉尼亚加密
    
    Args:
        plaintext: 明文字符串
        key: 密钥字符串
        
    Returns:
        加密后的字符串
    """
    processed_key = ''.join(filter(str.isalpha, key.upper()))
    
    if not processed_key:
        raise ValueError("密钥不能为空")
    
    ciphertext_chars = []
    key_length = len(processed_key)
    key_index = 0
    
    for char in plaintext:
        if char.isalpha():
            encrypted_char = _process_vigenere_char(char, processed_key[key_index % key_length], "encrypt")
            ciphertext_chars.append(encrypted_char)
            key_index += 1
        else:
            ciphertext_chars.append(char)
    
    return ''.join(ciphertext_chars)


def vigenere_decrypt(ciphertext, key):
    """
    维吉尼亚解密
    
    Args:
        ciphertext: 密文字符串
        key: 密钥字符串
        
    Returns:
        解密后的字符串
    """
    processed_key = ''.join(filter(str.isalpha, key.upper()))
    
    if not processed_key:
        raise ValueError("密钥不能为空")
    
    plaintext_chars = []
    key_length = len(processed_key)
    key_index = 0
    
    for char in ciphertext:
        if char.isalpha():
            decrypted_char = _process_vigenere_char(char, processed_key[key_index % key_length], "decrypt")
            plaintext_chars.append(decrypted_char)
            key_index += 1
        else:
            plaintext_chars.append(char)
    
    return ''.join(plaintext_chars)


def display_vigenere_table():
    """
    显示维吉尼亚加密表
    """
    alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
    
    print("维吉尼亚加密表:")
    print("   " + ' '.join(alphabet))
    print("  +" + "-" * 51)
    
    for i, row_start in enumerate(alphabet):
        row = []
        for j in range(26):
            # 计算每个位置的字符
            char = chr((ord(row_start) - ord('A') + j) % 26 + ord('A'))
            row.append(char)
        print(f"{row_start} | {' '.join(row)}")
    print()


def main():
    """
    主函数：交互式界面
    """
    print("=== 维吉尼亚加密工具 ===")
    
    while True:
        print("\n请选择操作:")
        print("1. 加密")
        print("2. 解密")
        print("3. 显示加密表")
        print("4. 退出")
        
        choice = input("请输入选择 (1-4): ").strip()
        
        if choice == '1':
            plaintext = input("请输入明文: ").strip()
            key = input("请输入密钥: ").strip()
            
            try:
                ciphertext = vigenere_encrypt(plaintext, key)
                print(f"加密结果: {ciphertext}")
            except Exception as e:
                print(f"加密错误: {e}")
                
        elif choice == '2':
            ciphertext = input("请输入密文: ").strip()
            key = input("请输入密钥: ").strip()
            
            try:
                plaintext = vigenere_decrypt(ciphertext, key)
                print(f"解密结果: {plaintext}")
            except Exception as e:
                print(f"解密错误: {e}")
                
        elif choice == '3':
            display_vigenere_table()
            
        elif choice == '4':
            print("退出程序。")
            break
            
        else:
            print("无效选择，请重新输入。")


if __name__ == "__main__":
    main()