package crypto

import (
	"encoding/base64"
	"encoding/hex"
	"fmt"
	"time"

	"github.com/tjfoc/gmsm/sm3"
	"github.com/tjfoc/gmsm/sm4"
)

// ==================== SM3 with Salt ====================

// SM3WithSalt 使用SM3加盐哈希
// 对应Java hutool的 SmUtil.sm3WithSalt(salt).digestHex(data)
// hutool实现为：SM3(salt + data)
func SM3WithSalt(salt string, data string) string {
	h := sm3.New()
	h.Write([]byte(salt))
	h.Write([]byte(data))
	return hex.EncodeToString(h.Sum(nil))
}

// ==================== SM4-ECB 加密/解密 ====================

// SM4ECBEncrypt SM4-ECB模式加密，返回base64编码字符串
func SM4ECBEncrypt(plaintext []byte, key []byte) (string, error) {
	if len(key) != 16 {
		return "", fmt.Errorf("SM4密钥长度必须为16字节")
	}

	block, err := sm4.NewCipher(key)
	if err != nil {
		return "", fmt.Errorf("创建SM4 cipher失败: %v", err)
	}

	padded := pkcs7Padding(plaintext, block.BlockSize())
	ciphertext := make([]byte, len(padded))
	for i := 0; i < len(padded); i += block.BlockSize() {
		block.Encrypt(ciphertext[i:i+block.BlockSize()], padded[i:i+block.BlockSize()])
	}

	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

// SM4ECBDecrypt SM4-ECB模式解密，输入base64编码字符串，返回明文
func SM4ECBDecrypt(encryptedData string, key []byte) ([]byte, error) {
	if len(key) != 16 {
		return nil, fmt.Errorf("SM4密钥长度必须为16字节")
	}

	ciphertext, err := base64.StdEncoding.DecodeString(encryptedData)
	if err != nil {
		return nil, fmt.Errorf("base64解码失败: %v", err)
	}

	block, err := sm4.NewCipher(key)
	if err != nil {
		return nil, fmt.Errorf("创建SM4 cipher失败: %v", err)
	}

	blockSize := block.BlockSize()
	if len(ciphertext)%blockSize != 0 {
		return nil, fmt.Errorf("密文长度不是块大小的整数倍")
	}

	plaintext := make([]byte, len(ciphertext))
	for i := 0; i < len(ciphertext); i += blockSize {
		block.Decrypt(plaintext[i:i+blockSize], ciphertext[i:i+blockSize])
	}

	plaintext, err = pkcs7UnPadding(plaintext)
	if err != nil {
		return nil, fmt.Errorf("去除填充失败: %v", err)
	}

	return plaintext, nil
}

// ==================== PKCS7 填充 ====================

func pkcs7Padding(data []byte, blockSize int) []byte {
	padding := blockSize - len(data)%blockSize
	padText := make([]byte, padding)
	for i := range padText {
		padText[i] = byte(padding)
	}
	return append(data, padText...)
}

func pkcs7UnPadding(data []byte) ([]byte, error) {
	if len(data) == 0 {
		return nil, fmt.Errorf("数据为空")
	}
	padding := int(data[len(data)-1])
	if padding > len(data) || padding == 0 {
		return nil, fmt.Errorf("无效的填充")
	}
	for i := len(data) - padding; i < len(data); i++ {
		if int(data[i]) != padding {
			return nil, fmt.Errorf("无效的填充")
		}
	}
	return data[:len(data)-padding], nil
}

// ==================== 时间戳工具 ====================

// GenerateTimestampMillis 生成毫秒级时间戳
func GenerateTimestampMillis() string {
	return fmt.Sprintf("%d", time.Now().UnixMilli())
}