package service

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

type AESGCMProtector struct {
	key []byte
}

func NewAESGCMProtectorFromBase64(keyB64 string) (*AESGCMProtector, error) {
	if keyB64 == "" {
		return nil, errors.New("empty key")
	}
	key, err := base64.StdEncoding.DecodeString(keyB64)
	if err != nil {
		return nil, err
	}
	if len(key) != 32 {
		return nil, errors.New("key must be 32 bytes (base64-encoded)")
	}
	return &AESGCMProtector{key: key}, nil
}

func (p *AESGCMProtector) Encrypt(plain []byte) ([]byte, error) {
	block, err := aes.NewCipher(p.key)
	if err != nil {
		return nil, err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}
	nonce := make([]byte, gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return nil, err
	}
	ciphertext := gcm.Seal(nonce, nonce, plain, nil)
	return ciphertext, nil
}

func (p *AESGCMProtector) Decrypt(ciphertext []byte) ([]byte, error) {
	block, err := aes.NewCipher(p.key)
	if err != nil {
		return nil, err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}
	if len(ciphertext) < gcm.NonceSize() {
		return nil, errors.New("ciphertext too short")
	}
	nonce := ciphertext[:gcm.NonceSize()]
	data := ciphertext[gcm.NonceSize():]
	return gcm.Open(nil, nonce, data, nil)
}
