using System.Runtime.InteropServices;
using System.ComponentModel;
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)
    {
        ParseHotkey(hotkey, out uint modifiers, out uint key);
        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);

            if (!RegisterHotKey(helper.Handle, HotkeyId, modifiers, key))
            {
                int error = Marshal.GetLastWin32Error();
                throw new InvalidOperationException(
                    $"Windows could not register hotkey '{Normalize(hotkey)}'. It may already be used by another app.",
                    new Win32Exception(error));
            }
        };

        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;
    }

    public static string Normalize(string hotkey)
    {
        ParseHotkey(hotkey, out uint modifiers, out uint key);
        Key parsedKey = KeyInterop.KeyFromVirtualKey((int)key);
        List<string> parts = [];

        if ((modifiers & 0x0002) != 0)
        {
            parts.Add("Ctrl");
        }

        if ((modifiers & 0x0001) != 0)
        {
            parts.Add("Alt");
        }

        if ((modifiers & 0x0004) != 0)
        {
            parts.Add("Shift");
        }

        if ((modifiers & 0x0008) != 0)
        {
            parts.Add("Win");
        }

        parts.Add(parsedKey.ToString());
        return string.Join("+", parts);
    }

    private static void ParseHotkey(string hotkey, out uint modifiers, out uint key)
    {
        modifiers = 0;
        key = 0;

        string[] parts = hotkey
            .Replace(",", "+", StringComparison.Ordinal)
            .Replace(" ", "+", StringComparison.Ordinal)
            .Split('+', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries);

        foreach (string part in parts)
        {
            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 (TryParseKey(part, out Key parsedKey))
            {
                key = (uint)KeyInterop.VirtualKeyFromKey(parsedKey);
            }
            else
            {
                throw new FormatException($"'{part}' is not a valid hotkey key.");
            }
        }

        if (modifiers == 0)
        {
            throw new FormatException("Hotkeys must include at least one modifier: Ctrl, Alt, Shift, or Win.");
        }

        if (key == 0)
        {
            throw new FormatException("Hotkeys must include a final key, such as Space, S, F12, or D1.");
        }
    }

    private static bool TryParseKey(string value, out Key key)
    {
        if (Enum.TryParse(value, true, out key))
        {
            return true;
        }

        if (value.Length == 1 && char.IsLetter(value[0]))
        {
            return Enum.TryParse(value.ToUpperInvariant(), out key);
        }

        if (value.Length == 1 && char.IsDigit(value[0]))
        {
            return Enum.TryParse($"D{value}", out key);
        }

        return false;
    }

    [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);
}