// +build windows

/*
Copyright 2021 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package app

import (
	"fmt"
	"os/user"

	"golang.org/x/sys/windows"
)

func isAdmin() (bool, error) {
	// Get current user
	u, err := user.Current()
	if err != nil {
		return false, fmt.Errorf("error retrieving current user: %s", err)
	}
	// Get IDs of group user is a member of
	ids, err := u.GroupIds()
	if err != nil {
		return false, fmt.Errorf("error retrieving group ids: %s", err)
	}

	// Check for existence of BUILTIN\ADMINISTRATORS group id
	for i := range ids {
		// BUILTIN\ADMINISTRATORS
		if "S-1-5-32-544" == ids[i] {
			return true, nil
		}
	}
	return false, nil
}

func checkPermissions() error {
	//https://github.com/golang/go/issues/28804#issuecomment-505326268
	var sid *windows.SID
	var userIsAdmin bool

	// https://docs.microsoft.com/en-us/windows/desktop/api/securitybaseapi/nf-securitybaseapi-checktokenmembership
	err := windows.AllocateAndInitializeSid(
		&windows.SECURITY_NT_AUTHORITY,
		2,
		windows.SECURITY_BUILTIN_DOMAIN_RID,
		windows.DOMAIN_ALIAS_RID_ADMINS,
		0, 0, 0, 0, 0, 0,
		&sid)
	if err != nil {
		return fmt.Errorf("error while checking for elevated permissions: %s", err)
	}

	//We must free the sid to prevent security token leaks
	defer windows.FreeSid(sid)
	token := windows.Token(0)

	userIsAdmin, err = isAdmin()
	if err != nil {
		return fmt.Errorf("error while checking admin group membership: %s", err)
	}

	member, err := token.IsMember(sid)
	if err != nil {
		return fmt.Errorf("error while checking for elevated permissions: %s", err)
	}
	if !member {
		return fmt.Errorf("kubelet needs to run with administrator permissions. Run as admin is: %t, User in admin group: %t", member, userIsAdmin)
	}

	return nil
}
