DesktopGuard.cs

// =============================================================================
// GPAL - Generally Positive Automation Library
// Copyright © 2026 Software Decisions, Inc. All rights reserved.
//
// This file is part of GPAL.
// Licensed under the Business Source License 1.1
//
// Primary development, architecture, and vision by Michael B. Vederman,
// CEO of Software Decisions, Inc., Texas.
//
// Internal development maintained privately.
// Public releases appear on GitHub: https://github.com/SoftwareDecisionsInc/GPAL.
//
// See LICENSE for full terms, including Additional Use Grant.
// =============================================================================
 
using System;
using System.Diagnostics;
using System.IO;
using static GenerallyPositive.Enums;
 
namespace GenerallyPositive.Browser
{
    internal static class DesktopGuard
    {
        internal const string ScriptName = "GPALReturnToDefaultDesktop.ps1";

        private const int DefaultDeadlineInSeconds = 600;
 
        // written next to the binary rather than kept as a file in the repo, so the copy that runs is always the
        // copy this version of GPAL means and is always beside whatever exe used a hidden desktop
        private const string script = @"param([int]$ParentPid = 0, [int]$DeadlineSeconds = 0)
 
# Puts the screen back on the Default desktop.
#
# GPAL writes this file next to the binary that used a hidden desktop, and runs it in the background while a
# peek is on, so a process that dies holding the screen still hands it back.
#
# Run it with no arguments to get a stranded screen back by hand. Nothing on a hidden desktop can launch it, so
# the way in is Ctrl+Alt+Del, Task Manager, File, Run new task, and the path to the .cmd beside this file.
 
Add-Type -Namespace GPAL -Name Desktops -MemberDefinition @'
[DllImport(""user32.dll"", SetLastError = true, CharSet = CharSet.Unicode)]
public static extern IntPtr OpenDesktop(string lpszDesktop, uint dwFlags, bool fInherit, uint dwDesiredAccess);
 
[DllImport(""user32.dll"", SetLastError = true)]
public static extern bool SwitchDesktop(IntPtr hDesktop);
 
[DllImport(""user32.dll"", SetLastError = true)]
public static extern bool CloseDesktop(IntPtr hDesktop);
'@
 
$DesktopSwitchDesktop = 0x0100
 
if ($ParentPid -gt 0) {
    $deadline = (Get-Date).AddSeconds($(if ($DeadlineSeconds -gt 0) { $DeadlineSeconds } else { 600 }))
 
    while ((Get-Date) -lt $deadline) {
        if ($null -eq (Get-Process -Id $ParentPid -ErrorAction SilentlyContinue)) { break }
 
        Start-Sleep -Milliseconds 500
    }
}
 
# switching to the desktop already on the screen does nothing, so this is safe whether anything is stranded or not
$default = [GPAL.Desktops]::OpenDesktop('Default', 0, $false, $DesktopSwitchDesktop)
 
if ($default -ne [IntPtr]::Zero) {
    [void][GPAL.Desktops]::SwitchDesktop($default)
    [void][GPAL.Desktops]::CloseDesktop($default)
}
";

        internal static string Folder
        {
            get { return AppDomain.CurrentDomain.BaseDirectory; }
        }

        internal static string Write()
        {
            string retVal = null;
            string path = Path.Combine(Folder, ScriptName);
 
            // caught rather than thrown, because a folder that cannot be written to is a reason to peek without
            // a guard and not a reason to fail the peek
            try
            {
                File.WriteAllText(path, script);
 
                retVal = path;
            }
            catch (Exception ex)
            {
                GPAL.PublishSimpleEvent(GPALEventType.EXCEPTION, $"Could not put the desktop recovery script in [{Folder}]", null, GPALObjectType.Browser, ex);
            }
 
            return retVal;
        }

        internal static Process Start(int forMs)
        {
            Process retVal = null;
            string path = Write();
 
            if (null != path)
            {
                int seconds = 0 < forMs ? (forMs / 1000) + 30 : DefaultDeadlineInSeconds;
 
                ProcessStartInfo starting = new ProcessStartInfo
                {
                    FileName = "powershell.exe",
                    Arguments = $"-NoProfile -NonInteractive -ExecutionPolicy Bypass -WindowStyle Hidden " +
                                $"-File \"{path}\" -ParentPid {Process.GetCurrentProcess().Id} -DeadlineSeconds {seconds}",
                    UseShellExecute = false,
                    CreateNoWindow = true,
                };
 
                // caught rather than thrown for the same reason Write catches: no guard is worse than a guard,
                // and both are better than no peek
                try
                {
                    retVal = Process.Start(starting);
                }
                catch (Exception ex)
                {
                    GPAL.PublishSimpleEvent(GPALEventType.EXCEPTION, $"Could not start the desktop guard from [{path}]", null, GPALObjectType.Browser, ex);
                }
            }
 
            return retVal;
        }

        internal static void Stop(Process guard)
        {
            if (null != guard)
            {
                // caught rather than thrown because this runs on the way out of a peek, where the screen is
                // already back and a stray powershell is not worth taking the caller down for
                try
                {
                    if (false == guard.HasExited)
                        guard.Kill();
                }
                catch (Exception ex)
                {
                    GPAL.PublishSimpleEvent(GPALEventType.EXCEPTION, "Could not stop the desktop guard", null, GPALObjectType.Browser, ex);
                }
 
                guard.Dispose();
            }
        }
    }
}