package cryptography

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"errors"
	"io"
)

func EncryptAESCBC(key, plaintext []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

	// Generate IV
	iv := make([]byte, aes.BlockSize)
	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
		return nil, err
	}

	// Add PKCS7 padding
	padding := aes.BlockSize - len(plaintext)%aes.BlockSize
	padtext := make([]byte, len(plaintext)+padding)
	copy(padtext, plaintext)
	for i := len(plaintext); i < len(padtext); i++ {
		padtext[i] = byte(padding)
	}

	// Encrypt
	mode := cipher.NewCBCEncrypter(block, iv)
	ciphertext := make([]byte, len(padtext))
	mode.CryptBlocks(ciphertext, padtext)

	return append(iv, ciphertext...), nil
}

func DecryptAESCBC(key, ciphertext []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

	if len(ciphertext) < aes.BlockSize {
		return nil, errors.New("ciphertext too short")
	}

	iv := ciphertext[:aes.BlockSize]
	ciphertext = ciphertext[aes.BlockSize:]

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

	mode := cipher.NewCBCDecrypter(block, iv)
	plaintext := make([]byte, len(ciphertext))
	mode.CryptBlocks(plaintext, ciphertext)

	// Remove PKCS7 padding
	padding := int(plaintext[len(plaintext)-1])
	return plaintext[:len(plaintext)-padding], nil
}