// backend\crypto.go

package main

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"io"
	"os"
	"path/filepath"
	"strings"
)

// Wir speichern den Key neben der EXE, damit encryption nach Neustart weiterhin entschlüsselbar ist.
// Datei enthält base64(32 bytes).
const settingsKeyFile = "recorder_settings.key"

func settingsKeyPath() string {
	if p, err := resolvePathRelativeToApp(settingsKeyFile); err == nil && strings.TrimSpace(p) != "" {
		return p
	}
	return settingsKeyFile
}

func loadOrCreateSettingsKey() ([]byte, error) {
	p := settingsKeyPath()

	// Load existing
	if b, err := os.ReadFile(p); err == nil {
		s := strings.TrimSpace(string(b))
		if s == "" {
			return nil, errors.New("settings key file ist leer")
		}
		key, err := base64.StdEncoding.DecodeString(s)
		if err != nil {
			return nil, err
		}
		if len(key) != 32 {
			return nil, errors.New("settings key muss 32 bytes sein")
		}
		return key, nil
	}

	// Create new
	key := make([]byte, 32)
	if _, err := io.ReadFull(rand.Reader, key); err != nil {
		return nil, err
	}

	enc := base64.StdEncoding.EncodeToString(key)

	// Ordner sicherstellen
	if dir := filepath.Dir(p); dir != "." && strings.TrimSpace(dir) != "" {
		_ = os.MkdirAll(dir, 0o755)
	}

	// best effort: Datei schreiben (für Windows perms gibt's hier keinen sauberen cross-platform chmod)
	if err := atomicWriteFile(p, []byte(enc+"\n")); err != nil {
		return nil, err
	}

	return key, nil
}

func encryptSettingString(plain string) (string, error) {
	key, err := loadOrCreateSettingsKey()
	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
	}

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

	ct := gcm.Seal(nil, nonce, []byte(plain), nil)
	out := append(nonce, ct...)
	return base64.StdEncoding.EncodeToString(out), nil
}

func decryptSettingString(enc string) (string, error) {
	enc = strings.TrimSpace(enc)
	if enc == "" {
		return "", nil
	}

	key, err := loadOrCreateSettingsKey()
	if err != nil {
		return "", err
	}

	raw, 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
	}

	ns := gcm.NonceSize()
	if len(raw) < ns+1 {
		return "", errors.New("ciphertext zu kurz")
	}
	nonce := raw[:ns]
	ct := raw[ns:]

	pt, err := gcm.Open(nil, nonce, ct, nil)
	if err != nil {
		return "", err
	}
	return string(pt), nil
}