using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;

namespace WindowNameChange
{
    class Program
    {
        [DllImport("user32.dll")]
        private static extern IntPtr FindWindow(string className, string windowName);

        [DllImport("user32.dll")]
        public static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, Int32 wParam, string lParam);

        private const int WM_SETTEXT = 0xC;

        [DllImport("user32.dll")]
        static extern bool SetWindowText(IntPtr hWnd, string text);

        delegate bool EnumWindowsProc(IntPtr hWnd, IntPtr lParam);

        [DllImport("user32.dll", SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        static extern bool EnumWindows(EnumWindowsProc lpEnumFunc, IntPtr lParam);

        [DllImport("user32.dll", SetLastError = true)]
        static extern int GetWindowText(IntPtr hWnd, StringBuilder lpString, int nMaxCount);

        [DllImport("user32.dll", SetLastError = true)]
        static extern int GetWindowTextLength(IntPtr hWnd);

        [DllImport("user32.dll", SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        static extern bool IsWindowVisible(IntPtr hWnd);

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


        static string GetWindowText(IntPtr hWnd)
        {
            int len = GetWindowTextLength(hWnd) + 1;
            StringBuilder sb = new StringBuilder(len);
            len = GetWindowText(hWnd, sb, len);
            return sb.ToString(0, len);
        }


        static void Main(string[] args)
        {
            EnumWindows((hWnd, lParam) =>
            {
                if (IsWindowVisible(hWnd) && GetWindowTextLength(hWnd) != 0)
                {
                    string title = GetWindowText(hWnd);
                    if (title.Contains("Word"))
                    {
                        Console.WriteLine(title);

                        string newTitle = "Блокнот-1";
                        IntPtr target_hwnd = hWnd;
                        Console.WriteLine("hwnd: " + target_hwnd);

                        SetForegroundWindow(target_hwnd);
                        SendMessage(target_hwnd, WM_SETTEXT, 0, newTitle);

                        //Console.WriteLine(SendMessage(target_hwnd, WM_SETTEXT, 0, "Калк"));

                        //SetWindowText(target_hwnd, newTitle);

                    }
                }
                return true;
            }, IntPtr.Zero);


            Console.Read();
        }
    }
}