using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Input;
using System.Windows.Interop;

namespace TaskbarLauncher.Services;

public sealed class HotkeyService : IDisposable
{
    private const int WmHotkey = 0x0312;
    private const int HotkeyId = 9001;

    private HwndSource? source;
    private Window? window;

    public event EventHandler? Pressed;

    public void Register(string hotkey)
    {
        Unregister();

        window = new Window
        {
            Width = 0,
            Height = 0,
            ShowInTaskbar = false,
            WindowStyle = WindowStyle.None,
            AllowsTransparency = true,
            Opacity = 0,
            Left = -10000,
            Top = -10000
        };

        window.SourceInitialized += (_, _) =>
        {
            var helper = new WindowInteropHelper(window);
            source = HwndSource.FromHwnd(helper.Handle);
            source?.AddHook(WndProc);

            ParseHotkey(hotkey, out uint modifiers, out uint key);
            RegisterHotKey(helper.Handle, HotkeyId, modifiers, key);
        };

        window.Show();
        window.Hide();
    }

    public void Unregister()
    {
        if (window is not null)
        {
            var helper = new WindowInteropHelper(window);
            if (helper.Handle != IntPtr.Zero)
            {
                UnregisterHotKey(helper.Handle, HotkeyId);
            }
        }

        source?.RemoveHook(WndProc);
        source = null;
        window?.Close();
        window = null;
    }

    public void Dispose()
    {
        Unregister();
    }

    private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
    {
        if (msg == WmHotkey && wParam.ToInt32() == HotkeyId)
        {
            Pressed?.Invoke(this, EventArgs.Empty);
            handled = true;
        }

        return IntPtr.Zero;
    }

    private static void ParseHotkey(string hotkey, out uint modifiers, out uint key)
    {
        modifiers = 0;
        key = (uint)KeyInterop.VirtualKeyFromKey(Key.Space);

        foreach (string part in hotkey.Split('+', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries))
        {
            if (part.Equals("Ctrl", StringComparison.OrdinalIgnoreCase) || part.Equals("Control", StringComparison.OrdinalIgnoreCase))
            {
                modifiers |= 0x0002;
            }
            else if (part.Equals("Alt", StringComparison.OrdinalIgnoreCase))
            {
                modifiers |= 0x0001;
            }
            else if (part.Equals("Shift", StringComparison.OrdinalIgnoreCase))
            {
                modifiers |= 0x0004;
            }
            else if (part.Equals("Win", StringComparison.OrdinalIgnoreCase))
            {
                modifiers |= 0x0008;
            }
            else if (Enum.TryParse(part, true, out Key parsedKey))
            {
                key = (uint)KeyInterop.VirtualKeyFromKey(parsedKey);
            }
        }
    }

    [DllImport("user32.dll", SetLastError = true)]
    private static extern bool RegisterHotKey(IntPtr hWnd, int id, uint fsModifiers, uint vk);

    [DllImport("user32.dll", SetLastError = true)]
    private static extern bool UnregisterHotKey(IntPtr hWnd, int id);
}