﻿using System;
using System.Diagnostics;
using System.Runtime.InteropServices;

namespace GongSolutions.Wpf.DragDrop.Utilities
{
    // Taken from Fluent Drag&Drop https://github.com/punker76/FluentDragDrop
    internal static class MouseHelper
    {
        private delegate IntPtr LowLevelMouseProc(int nCode, IntPtr wParam, IntPtr lParam);

        private const int WH_MOUSE_LL = 14;

        private static IntPtr _hookID = IntPtr.Zero;
        private static Action<System.Windows.Point> _mouseMoveHandler;

        // wee need to keep the variable to prevent the GarbageCollector to remove the HookCallback
        // https://social.msdn.microsoft.com/Forums/vstudio/en-US/68fdc3dc-8d77-48c4-875c-5312baa56aee/how-to-fix-callbackoncollecteddelegate-exception?forum=netfxbcl
        private static LowLevelMouseProc _proc = HookCallback;

        internal static IntPtr HookMouseMove(Action<System.Windows.Point> mouseMoveHandler)
        {
            _mouseMoveHandler = mouseMoveHandler;

            using (var process = Process.GetCurrentProcess())
            {
                using (var module = process.MainModule)
                {
                    return SetWindowsHookEx(WH_MOUSE_LL, _proc, GetModuleHandle(module.ModuleName), 0);
                }
            }
        }

        internal static void RemoveHook(IntPtr hookId)
        {
            UnhookWindowsHookEx(hookId);
        }

        private static IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
        {
            if (nCode >= 0 && MouseMessages.WM_MOUSEMOVE == (MouseMessages)wParam)
            {
                MSLLHOOKSTRUCT hookStruct = (MSLLHOOKSTRUCT)Marshal.PtrToStructure(lParam, typeof(MSLLHOOKSTRUCT));
                //Debug.WriteLine(hookStruct.pt.x + ", " + hookStruct.pt.y);
                var mousePosScreen = new System.Windows.Point(hookStruct.pt.x, hookStruct.pt.y);
                _mouseMoveHandler?.Invoke(mousePosScreen);
            }

            return CallNextHookEx(_hookID, nCode, wParam, lParam);
        }

        private enum MouseMessages
        {
            WM_LBUTTONDOWN = 0x0201,
            WM_LBUTTONUP = 0x0202,
            WM_MOUSEMOVE = 0x0200,
            WM_MOUSEWHEEL = 0x020A,
            WM_RBUTTONDOWN = 0x0204,
            WM_RBUTTONUP = 0x0205
        }

        [StructLayout(LayoutKind.Sequential)]
        private struct POINT
        {
            public int x;
            public int y;
        }

        [StructLayout(LayoutKind.Sequential)]
        private struct MSLLHOOKSTRUCT
        {
            public POINT pt;
            public uint mouseData;
            public uint flags;
            public uint time;
            public IntPtr dwExtraInfo;
        }

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr SetWindowsHookEx(int idHook, LowLevelMouseProc lpfn, IntPtr hMod, uint dwThreadId);

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        private static extern bool UnhookWindowsHookEx(IntPtr hhk);

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

        [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr GetModuleHandle(string lpModuleName);
    }
}