Program.cs

// SPDX-License-Identifier: GPL-3.0-or-later
// Copyright (C) 2026 YJZ

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Threading;
using System.Windows.Forms;

namespace FolderEncryptor
{
    internal static class Program
    {
        private const string MutexName = "Local\\YJZFolderEncryptorSingleInstance";
        private const string ActivateEventName = "Local\\YJZFolderEncryptorActivate";
        private const int SW_RESTORE = 9;

        [STAThread]
        private static void Main()
        {
            bool createdNew;
            using (Mutex mutex = new Mutex(true, MutexName, out createdNew))
            {
                if (!createdNew)
                {
                    SignalExistingInstance();
                    FocusExistingProcessWindow();
                    return;
                }

                using (EventWaitHandle activateEvent = new EventWaitHandle(false, EventResetMode.AutoReset, ActivateEventName))
                {
                    Application.EnableVisualStyles();
                    Application.SetCompatibleTextRenderingDefault(false);

                    MainForm form = new MainForm();
                    StartActivationThread(form, activateEvent);
                    Application.Run(form);
                    GC.KeepAlive(mutex);
                }
            }
        }

        private static void StartActivationThread(MainForm form, EventWaitHandle activateEvent)
        {
            Thread thread = new Thread(delegate()
            {
                while (!form.IsDisposed)
                {
                    activateEvent.WaitOne();
                    if (form.IsDisposed)
                        return;

                    try
                    {
                        form.BeginInvoke(new MethodInvoker(form.ShowEncryptTabAndBringToFront));
                    }
                    catch (InvalidOperationException)
                    {
                        return;
                    }
                }
            });
            thread.IsBackground = true;
            thread.Name = "FolderEncryptorActivation";
            thread.Start();
        }

        private static void SignalExistingInstance()
        {
            try
            {
                EventWaitHandle activateEvent = EventWaitHandle.OpenExisting(ActivateEventName);
                activateEvent.Set();
                activateEvent.Close();
            }
            catch (WaitHandleCannotBeOpenedException)
            {
            }
        }

        private static void FocusExistingProcessWindow()
        {
            Process current = Process.GetCurrentProcess();
            Process[] processes = Process.GetProcessesByName(current.ProcessName);

            for (int attempt = 0; attempt < 20; attempt++)
            {
                foreach (Process process in processes)
                {
                    if (process.Id == current.Id)
                        continue;

                    IntPtr handle = process.MainWindowHandle;
                    if (handle == IntPtr.Zero)
                        continue;

                    if (IsIconic(handle))
                        ShowWindow(handle, SW_RESTORE);
                    SetForegroundWindow(handle);
                    return;
                }

                Thread.Sleep(100);
                processes = Process.GetProcessesByName(current.ProcessName);
            }
        }

        [DllImport("user32.dll")]
        private static extern bool SetForegroundWindow(IntPtr hWnd);

        [DllImport("user32.dll")]
        private static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

        [DllImport("user32.dll")]
        private static extern bool IsIconic(IntPtr hWnd);
    }
}