using System;
using System.ComponentModel;
using System.Drawing;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace Ace.UI.Forms {
    public partial class ProcessSelector : UserControl {
        #region Imports
        private delegate int HookProc(int nCode, IntPtr wParam, IntPtr lParam);

        private const int WH_MOUSE_LL = 14;
        private const int WM_LBUTTONUP = 0x202;
        
        [DllImport("user32.dll")]
        private static extern IntPtr SetWindowsHookEx(int hookType, HookProc lpfn, IntPtr hMod, int dwThreadId);

        [DllImport("user32.dll")]
        private static extern bool UnhookWindowsHookEx(IntPtr idHook);
		
        [DllImport("user32.dll")]
        private static extern int CallNextHookEx(IntPtr idHook, int nCode, IntPtr wParam, IntPtr lParam);

        [DllImport("user32.dll")]
        private static extern IntPtr WindowFromPoint(Point p);

        [DllImport("user32.dll")]
        private static extern IntPtr GetAncestor(IntPtr hwnd, uint flags);

        [DllImport("user32.dll")]
        private static extern uint GetWindowThreadProcessId(IntPtr hWnd, out int processId);
        #endregion

        #region Properties
        public Process SelectedProcess { get; private set; }
        #endregion

        #region Fields
        private readonly HookProc _mouseHookProcedure;
        private IntPtr _hookId;
        private bool _dragging;
        #endregion

        public ProcessSelector() {
            InitializeComponent();
            Disposed += OnDisposed;
            _mouseHookProcedure = OnMouseEvent;
        }

        private void OnDisposed(object sender, EventArgs e) {
            UnhookMouseEvents();
        }
        
        private void TargetImage_MouseDown(object sender, MouseEventArgs e) {
            HookMouseEvents();
            _dragging = true;
            DoDragDrop(sender, DragDropEffects.None);
        }

        private int OnMouseEvent(int nCode, IntPtr wParam, IntPtr lParam) {
            if (_dragging && wParam.ToInt32() == WM_LBUTTONUP) {
                var window = GetAncestor(WindowFromPoint(MousePosition), 2);
                int processId;
                GetWindowThreadProcessId(window, out processId);
                var process = Process.GetProcessById(processId);
                
                _dragging = false;
                SetProcessInfo(process);
            }
            
            return CallNextHookEx(_hookId, nCode, wParam, lParam);
        }

        private void HookMouseEvents() {
            _hookId = SetWindowsHookEx(WH_MOUSE_LL, _mouseHookProcedure, IntPtr.Zero, 0);
            if (_hookId == IntPtr.Zero)
                throw new Win32Exception("Cannot perform SetWindowsHookEx.");
        }

        private void UnhookMouseEvents() {
            if (_hookId == IntPtr.Zero)
                return;

            UnhookWindowsHookEx(_hookId);
            _hookId = IntPtr.Zero;
        }

        private void SetProcessInfo(Process process) {
            if (InvokeRequired) {
                Invoke((Action<Process>) SetProcessInfo, process);
                return;
            }

            UnhookMouseEvents();

            if (process.Id == Process.GetCurrentProcess().Id)
                return;

            ProcessIdValue.Text = process.Id.ToString();
            ProcessNameValue.Text = process.ProcessName + ".exe";
            SelectedProcess = process;
        }
    }
}