package settings

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

func seal(plaintext []byte, key []byte) (nonce []byte, ciphertext []byte, err error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, nil, fmt.Errorf("aes cipher: %w", err)
	}

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, nil, fmt.Errorf("gcm: %w", err)
	}

	nonce = make([]byte, gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return nil, nil, fmt.Errorf("nonce: %w", err)
	}

	ciphertext = gcm.Seal(nil, nonce, plaintext, nil)
	return nonce, ciphertext, nil
}

func open(nonce []byte, ciphertext []byte, key []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, fmt.Errorf("aes cipher: %w", err)
	}

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, fmt.Errorf("gcm: %w", err)
	}

	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return nil, fmt.Errorf("decrypt: %w", err)
	}
	return plaintext, nil
}

func decodeKey(base64Key string) ([]byte, error) {
	key, err := base64.StdEncoding.DecodeString(base64Key)
	if err != nil {
		return nil, fmt.Errorf("decode key: %w", err)
	}
	if length := len(key); length != 16 && length != 24 && length != 32 {
		return nil, fmt.Errorf("key must be 16, 24, or 32 bytes after base64 decode, got %d", length)
	}
	return key, nil
}