using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using System.Threading.Tasks;
using System.Windows.Forms;
using PInvoke;

namespace WF_Invoke
{
    static class Program
    {
        delegate bool EnumThreadDelegate(IntPtr hWnd, IntPtr lParam);

        [DllImport("user32.dll")]
        static extern bool EnumThreadWindows(int dwThreadId, EnumThreadDelegate lpfn, IntPtr lParam);

        public delegate bool EnumWindowsProc(IntPtr hwnd, IntPtr lParam);

        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool EnumChildWindows(IntPtr hwndParent, EnumWindowsProc lpEnumFunc, IntPtr lParam);

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, string lParam);

        [STAThread]
        static void Main()
        {
            // get process by exe name
            // var snapshot = Kernel32.CreateToolhelp32Snapshot(Kernel32.CreateToolhelp32SnapshotFlags.TH32CS_SNAPALL, 0);
            // var process = Kernel32.Process32First(snapshot);
            // while (process.HasValue)
            // {
            //     if (string.Compare(process.Value.ExeFile, "notepad.exe") == 0) break;
            //     process = Kernel32.Process32Next(snapshot);
            // }
            // snapshot.Dispose();
            //
            // var processId = process.Value.th32ProcessID;
            //
            var handles = new List<IntPtr>();
            foreach (ProcessThread thread in Process.GetProcesses().First(p => string.Compare(p.ProcessName, "notepad") == 0).Threads)
                EnumThreadWindows(thread.Id, (hWnd, lParam) =>
                {
                    handles.Add(hWnd);
                    return true;
                }, IntPtr.Zero);

            foreach (var handle in handles)
            {
                EnumChildWindows(handle, (hwnd, param) =>
                {
                    User32.WINDOWINFO winInfo = User32.WINDOWINFO.Create();
                    User32.GetWindowInfo(hwnd, ref winInfo);
                    var className = User32.GetClassName(hwnd);
                    if (className == "Edit" && winInfo.dwStyle == 0x50200104)
                    {
                        SendMessage(hwnd, (uint) User32.WindowMessage.WM_SETTEXT, IntPtr.Zero, "Hello");
                        return false;
                    }

                    Trace.WriteLine(hwnd + ": " + className);
                    return true;
                }, IntPtr.Zero);
            }
        }
    }
}