// internal/shared/crypto/encryption.go
package crypto

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"io"
	"os"
	"crypto/sha256"
)

func Encrypt(plain string) (string, error) {
	key := []byte(os.Getenv("SESSION_SECRET"))
	if len(key) != 32 {
		return "", errors.New("SESSION_SECRET must be 32 bytes")
	}

	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(plain), nil)
	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

func Decrypt(enc string) (string, error) {
	key := []byte(os.Getenv("SESSION_SECRET"))
	data, err := base64.StdEncoding.DecodeString(enc)
	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(data) < nonceSize {
		return "", errors.New("invalid ciphertext")
	}

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

	return string(plain), nil
}

func SHA256Base64URL(input string) string {
	hash := sha256.Sum256([]byte(input))
	return base64.RawURLEncoding.EncodeToString(hash[:])
}