package codec

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"io"
)

func EncryptPayload(key []byte, plaintext []byte) ([]byte, []byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, nil, err
	}
	aesGCM, err := cipher.NewGCM(block)
	if err != nil {
		return nil, nil, err
	}
	nonce := make([]byte, aesGCM.NonceSize())
	if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
		return nil, nil, err
	}
	ciphertext := aesGCM.Seal(nil, nonce, plaintext, nil)
	return ciphertext, nonce, nil
}

func DecryptPayload(key []byte, ciphertext []byte, nonce []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	aesGCM, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}
	return aesGCM.Open(nil, nonce, ciphertext, nil)
}

func CalculateHMAC(key []byte, data []byte) string {
	h := hmac.New(sha256.New, key)
	h.Write(data)
	return hex.EncodeToString(h.Sum(nil))
}

func VerifyHMAC(key []byte, data []byte, receivedHMAC string) bool {
	expectedHMAC := CalculateHMAC(key, data)
	return hmac.Equal([]byte(expectedHMAC), []byte(receivedHMAC))
}