using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
// 以下の名前空間をインポートする
using System.Diagnostics;
using System.Runtime.InteropServices;

namespace ProcessShowPrevProcess
{
    public partial class Form1 : Form
    {
        public class MyProcess
        {


            [DllImport("USER32.DLL", CharSet = CharSet.Auto)]
            private static extern int ShowWindow(
                System.IntPtr hWnd,
                int nCmdShow
            );


            [DllImport("USER32.DLL", CharSet = CharSet.Auto)]
            private static extern bool SetForegroundWindow(
                System.IntPtr hWnd
            );


            private const int SW_NORMAL = 1;


            /// ------------------------------------------------------------------------------------
            /// <summary>
            ///     同名のプロセスが起動中の場合、メイン ウィンドウをアクティブにします。</summary>
            /// <returns>
            ///     既に起動中であれば true。それ以外は false。</returns>
            /// ------------------------------------------------------------------------------------
            public static bool ShowPrevProcess()
            {
                Process hThisProcess = Process.GetCurrentProcess();
                Process[] hProcesses = Process.GetProcessesByName(hThisProcess.ProcessName);
                int iThisProcessId = hThisProcess.Id;

                foreach (Process hProcess in hProcesses)
                {
                    if (hProcess.Id != iThisProcessId)
                    {
                        ShowWindow(hProcess.MainWindowHandle, SW_NORMAL);
                        SetForegroundWindow(hProcess.MainWindowHandle);
                        return true;
                    }
                }

                return false;
            }
        }

        [System.STAThread()]
        private static void Main()
        {
            // 同名のプロセスが起動していない時は起動する
            if (!MyProcess.ShowPrevProcess())
            {
                Application.Run(new Form1());
            }
        }
    }
}