// Filename: internal/crypto/crypto.go
package crypto

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"gemini-balancer/internal/config" // [NEW] Crypto service now depends on Config
	"io"
	"os"
)

type Service struct {
	gcm cipher.AEAD
}

func NewService(cfg *config.Config) (*Service, error) {
	keyHex := cfg.EncryptionKey
	if keyHex == "" {
		// Fallback to environment variable if not in config file
		keyHex = os.Getenv("ENCRYPTION_KEY")
		if keyHex == "" {
			return nil, fmt.Errorf("encryption key is not configured: please set 'encryption_key' in config.yaml or the ENCRYPTION_KEY environment variable")
		}
	}
	key, err := hex.DecodeString(keyHex)
	if err != nil {
		return nil, fmt.Errorf("failed to decode encryption key from hex: %w", err)
	}
	if len(key) != 32 {
		return nil, fmt.Errorf("invalid encryption key length: must be 32 bytes (64 hex characters), got %d bytes", len(key))
	}
	block, err := aes.NewCipher(key)
	if err != nil { // ... (rest is the same)
		return nil, fmt.Errorf("failed to create AES cipher block: %w", err)
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, fmt.Errorf("failed to create GCM block cipher: %w", err)
	}
	return &Service{gcm: gcm}, nil
}

// Encrypt encrypts plaintext and returns hex-encoded ciphertext.
func (s *Service) Encrypt(plaintext string) (string, error) {
	nonce := make([]byte, s.gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", fmt.Errorf("failed to generate nonce: %w", err)
	}

	ciphertext := s.gcm.Seal(nonce, nonce, []byte(plaintext), nil)
	return hex.EncodeToString(ciphertext), nil
}

// Decrypt decrypts a hex-encoded ciphertext and returns the plaintext.
func (s *Service) Decrypt(hexCiphertext string) (string, error) {
	ciphertext, err := hex.DecodeString(hexCiphertext)
	if err != nil {
		return "", fmt.Errorf("ciphertext hex decode error: %w", err)
	}

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

	nonce, encryptedMessage := ciphertext[:nonceSize], ciphertext[nonceSize:]
	plaintext, err := s.gcm.Open(nil, nonce, encryptedMessage, nil)
	if err != nil {
		return "", fmt.Errorf("failed to decrypt: %w", err)
	}

	return string(plaintext), nil
}