package services

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

type CryptoService struct {
	gcm cipher.AEAD
}

func NewCryptoService(rawKey string) (*CryptoService, error) {
	key := []byte(rawKey)
	if len(key) < 32 {
		padded := make([]byte, 32)
		copy(padded, key)
		key = padded
	}
	if len(key) > 32 {
		key = key[:32]
	}

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

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

	return &CryptoService{gcm: gcm}, nil
}

func (c *CryptoService) Encrypt(plain string) (string, error) {
	nonce := make([]byte, c.gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", err
	}

	ciphertext := c.gcm.Seal(nonce, nonce, []byte(plain), nil)
	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

func (c *CryptoService) Decrypt(token string) (string, error) {
	raw, err := base64.StdEncoding.DecodeString(token)
	if err != nil {
		return "", err
	}

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

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

	return string(plain), nil
}
