package cryptoutil

import (
	"crypto/aes"
	"crypto/cipher"
	"encoding/base64"
)

const (
	scAESKey = "m1xp9slgfa|su@m2"
	scAESIV  = "pa!st17m@04h5u#0"
)

// EncryptSC AES-CBC加密，使用固定的key和iv
func EncryptSC(plaintext string) string {
	key := []byte(scAESKey)
	iv := []byte(scAESIV)

	block, err := aes.NewCipher(key)
	if err != nil {
		return ""
	}

	// PKCS7填充
	blockSize := block.BlockSize()
	padding := blockSize - len(plaintext)%blockSize
	padText := make([]byte, padding)
	for i := range padText {
		padText[i] = byte(padding)
	}
	plaintextBytes := append([]byte(plaintext), padText...)

	// CBC加密
	ciphertext := make([]byte, len(plaintextBytes))
	mode := cipher.NewCBCEncrypter(block, iv)
	mode.CryptBlocks(ciphertext, plaintextBytes)

	// Base64编码
	return base64.StdEncoding.EncodeToString(ciphertext)
}

// DecryptSC AES-CBC解密，使用固定的key和iv
func DecryptSC(ciphertext string) string {
	key := []byte(scAESKey)
	iv := []byte(scAESIV)

	// Base64解码
	ciphertextBytes, err := base64.StdEncoding.DecodeString(ciphertext)
	if err != nil {
		return ""
	}

	block, err := aes.NewCipher(key)
	if err != nil {
		return ""
	}

	// CBC解密
	blockSize := block.BlockSize()
	if len(ciphertextBytes)%blockSize != 0 {
		return ""
	}

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

	// 去除PKCS7填充
	if len(plaintext) == 0 {
		return ""
	}
	padding := int(plaintext[len(plaintext)-1])
	if padding <= 0 || padding > blockSize || padding > len(plaintext) {
		return ""
	}

	return string(plaintext[:len(plaintext)-padding])
}