package pass

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"fmt"
	"os"

	"golang.org/x/crypto/scrypt"
)

func DeriveKey(password, salt []byte) ([]byte, []byte, error) {
	if salt == nil {
		salt = make([]byte, 32)
		if _, err := rand.Read(salt); err != nil {
			return nil, nil, err
		}
	}

	key, err := scrypt.Key(password, salt, 32768, 8, 1, 32)
	if err != nil {
		return nil, nil, fmt.Errorf("błąd generowania klucza: %w", err)
	}

	return key, salt, nil
}

func Encrypt(key, data []byte) ([]byte, error) {
	blockCipher, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

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

	nonce := make([]byte, gcm.NonceSize())
	if _, err = rand.Read(nonce); err != nil {
		return nil, err
	}

	ciphertext := gcm.Seal(nonce, nonce, data, nil)

	return ciphertext, nil
}

func Decrypt(key, data []byte) ([]byte, error) {
	blockCipher, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

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

	nonce, ciphertext := data[:gcm.NonceSize()], data[gcm.NonceSize():]

	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return nil, err
	}

	return plaintext, nil
}

func DecryptFile(password []byte, file string) ([]byte, error) {
	data, err := os.ReadFile(file)
	if err != nil {
		return nil, err
	}
	salt := data[:32] //
	data = data[32:]
	key, _, err := DeriveKey(password, salt)
	if err != nil {
		return nil, err
	}
	return Decrypt(key, data)
}

func EncryptFile(password []byte, file string, data []byte) error {
	key, salt, err := DeriveKey(password, nil)
	if err != nil {
		return err
	}
	encrypted, err := Encrypt(key, data)
	if err != nil {
		return err
	}
	fd, err := os.Create(file)
	if err != nil {
		return err
	}
	_, err = fd.Write(salt)
	if err != nil {
		return err
	}
	_, err = fd.Write(encrypted)
	if err != nil {
		return err
	}
	return fd.Close()
}