package crypto

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"io"
	"lain/config"
)

func getKey() []byte {
	hash := sha256.Sum256([]byte(config.Server.AppSecret))
	return hash[:]
}

func Encrypt(plaintext string) (string, error) {
	key := getKey()

	block, err := aes.NewCipher(key)
	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.URLEncoding.EncodeToString(ciphertext), nil
}

func Decrypt(ciphertext string) (string, error) {
	key := getKey()

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

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

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

	nonceSize := gcm.NonceSize()
	if len(ciphertextBytes) < nonceSize {
		return "", fmt.Errorf("ciphertext too short")
	}

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

	return string(plaintextBytes), nil
}