package encryption

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"fmt"
)

type AesCBCWithPadding struct {
	key []byte
	iv  []byte
}

func NewAesCBCWithPadding(key, iv []byte) *AesCBCWithPadding {
	return &AesCBCWithPadding{
		key: key,
		iv:  iv,
	}
}

// ZeroPadding 填充（填充0x00到块大小）
func zeroPad(data []byte, blockSize int) []byte {
	padding := blockSize - len(data)%blockSize
	padText := bytes.Repeat([]byte{0}, padding)
	return append(data, padText...)
}

// ZeroUnPadding 去除填充的0x00
func zeroUnPad(data []byte) []byte {
	return bytes.TrimRightFunc(data, func(r rune) bool {
		return r == rune(0)
	})
}

// AES加密函数
func (a *AesCBCWithPadding) Encrypt(plaintext []byte) ([]byte, error) {
	block, err := aes.NewCipher(a.key)
	if err != nil {
		return nil, err
	}

	//if len(plaintext)%aes.BlockSize != 0 {
	//	return nil, fmt.Errorf("plaintext is not a multiple of the block size")
	//}

	plaintext = zeroPad(plaintext, aes.BlockSize)

	ciphertext := make([]byte, aes.BlockSize+len(plaintext))
	copy(ciphertext[:aes.BlockSize], a.iv)
	mode := cipher.NewCBCEncrypter(block, a.iv)
	mode.CryptBlocks(ciphertext, plaintext)

	return ciphertext, nil
}

// AES解密函数
func (a *AesCBCWithPadding) Decrypt(ciphertext []byte) ([]byte, error) {
	block, err := aes.NewCipher(a.key)
	if err != nil {
		return nil, err
	}

	if len(ciphertext)%aes.BlockSize != 0 {
		return nil, fmt.Errorf("ciphertext is not a multiple of the block size")
	}

	decrypted := make([]byte, len(ciphertext))
	copy(decrypted, ciphertext)

	mode := cipher.NewCBCDecrypter(block, a.iv)
	mode.CryptBlocks(decrypted, ciphertext)

	plaintext := zeroUnPad(decrypted)
	return plaintext, nil
}