package utils

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"io"
	"log"
	"os"
)

var encryptKey []byte

func init() {
	key := os.Getenv("ENCRYPT_KEY")
	if key == "" {
		key = "lan-manager-default-key-change-in-production"
		log.Println("[WARN] ENCRYPT_KEY not set, using default key. Please set ENCRYPT_KEY in production.")
	}
	h := sha256.Sum256([]byte(key))
	encryptKey = h[:]
}

// Encrypt 使用 AES-GCM 加密明文，返回 base64 编码的密文
func Encrypt(plaintext string) (string, error) {
	if plaintext == "" {
		return "", nil
	}
	block, err := aes.NewCipher(encryptKey)
	if err != nil {
		return "", err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}
	nonce := make([]byte, gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", err
	}
	ciphertext := gcm.Seal(nonce, nonce, []byte(plaintext), nil)
	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

// Decrypt 使用 AES-GCM 解密密文，输入为 base64 编码。
// 为了兼容升级前的明文密码，如果 base64 解码失败或解密失败，则直接返回原始字符串。
func Decrypt(ciphertext string) (string, error) {
	if ciphertext == "" {
		return "", nil
	}
	data, err := base64.StdEncoding.DecodeString(ciphertext)
	if err != nil {
		// 兼容旧明文密码
		return ciphertext, nil
	}
	block, err := aes.NewCipher(encryptKey)
	if err != nil {
		return "", err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}
	nonceSize := gcm.NonceSize()
	if len(data) < nonceSize {
		// 兼容旧明文密码
		return ciphertext, nil
	}
	nonce, cipherData := data[:nonceSize], data[nonceSize:]
	plain, err := gcm.Open(nil, nonce, cipherData, nil)
	if err != nil {
		// 兼容旧明文密码
		return ciphertext, nil
	}
	return string(plain), nil
}