package crypto

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"io"
)

// Encrypt 使用 AES-256-GCM 加密明文，返回 base64 编码的密文
func Encrypt(plaintext, key string) (string, error) {
	keyBytes := []byte(key)
	if len(keyBytes) != 32 {
		return "", errors.New("encrypt key must be 32 bytes")
	}

	block, err := aes.NewCipher(keyBytes)
	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-256-GCM 解密
func Decrypt(ciphertextB64, key string) (string, error) {
	keyBytes := []byte(key)
	if len(keyBytes) != 32 {
		return "", errors.New("decrypt key must be 32 bytes")
	}

	ciphertext, err := base64.StdEncoding.DecodeString(ciphertextB64)
	if err != nil {
		return "", err
	}

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

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}

	nonceSize := gcm.NonceSize()
	if len(ciphertext) < nonceSize {
		return "", errors.New("ciphertext too short")
	}

	nonce, ciphertext := ciphertext[:nonceSize], ciphertext[nonceSize:]
	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return "", err
	}

	return string(plaintext), nil
}