package payment

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

var encryptionKey []byte

func InitEncryptionKey(key string) {
	encryptionKey = []byte(key)
}

func Encrypt(plaintext string) (string, error) {
	gcm, err := newGCM()
	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
}

func Decrypt(encoded string) (string, error) {
	gcm, err := newGCM()
	if err != nil {
		return "", err
	}

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

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

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

	return string(plaintext), nil
}

func newGCM() (cipher.AEAD, error) {
	if len(encryptionKey) != 32 {
		return nil, fmt.Errorf("invalid encryption key length: got %d, want 32", len(encryptionKey))
	}

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

	return cipher.NewGCM(block)
}