package crypto

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

func Encrypt(key, plaintext []byte) (string, error) {
	gcm, err := newGCM(key)
	if err != nil {
		return "", err
	}
	nonce := make([]byte, gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", err
	}
	ct := gcm.Seal(nonce, nonce, plaintext, nil)
	return base64.StdEncoding.EncodeToString(ct), nil
}

func Decrypt(key []byte, enc string) ([]byte, error) {
	gcm, err := newGCM(key)
	if err != nil {
		return nil, err
	}
	raw, err := base64.StdEncoding.DecodeString(enc)
	if err != nil {
		return nil, err
	}
	ns := gcm.NonceSize()
	if len(raw) < ns {
		return nil, errors.New("ciphertext too short")
	}
	return gcm.Open(nil, raw[:ns], raw[ns:], nil)
}

func newGCM(key []byte) (cipher.AEAD, error) {
	if len(key) != 32 {
		return nil, errors.New("key must be 32 bytes (AES-256)")
	}
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	return cipher.NewGCM(block)
}