using System.Runtime.InteropServices;

namespace CursorLang.Interop;

/// <summary>
/// Win32 API for the notification area: the icon itself, the messages it sends
/// and the icon image taken from the executable.
/// </summary>
/// <remarks>
/// The icon is asked for at version 4 of the protocol. It is the only version that
/// reports a request for the context menu as such — by the keyboard as well as by
/// the right button — and passes the point of the click along with it. The
/// notification then arrives in the low word of <c>lParam</c>, and the point in
/// <c>wParam</c>, which is the opposite of the earlier versions.
/// </remarks>
internal static class TrayIconNative
{
    /// <summary>The message the icon sends to its window. WM_APP is free for the app.</summary>
    internal const int CallbackMessage = 0x8000 + 1;

    /// <summary>The user chose the icon: a click of the left button or Enter on it.</summary>
    internal const int SelectNotification = 0x0400;

    /// <summary>The same by the space bar — Windows tells the two apart.</summary>
    internal const int KeySelectNotification = 0x0403;

    /// <summary>The context menu is asked for: the right button or the menu key.</summary>
    internal const int ContextMenuNotification = 0x007B;

    private const int NIM_ADD = 0x00000000;
    private const int NIM_MODIFY = 0x00000001;
    private const int NIM_DELETE = 0x00000002;
    private const int NIM_SETVERSION = 0x00000004;

    private const uint NIF_MESSAGE = 0x00000001;
    private const uint NIF_ICON = 0x00000002;
    private const uint NIF_TIP = 0x00000004;
    private const uint NIF_SHOWTIP = 0x00000080;

    private const uint NotifyIconVersion4 = 4;

    private const uint IMAGE_ICON = 1;
    private const uint LR_DEFAULTCOLOR = 0x00000000;

    private const int SM_CXSMICON = 49;
    private const int SM_CYSMICON = 50;

    /// <summary>The resource the .NET build puts the application icon under.</summary>
    private const int ApplicationIconResource = 32512;

    /// <summary>
    /// Explorer says it has restarted this way. The icons of every application are
    /// gone by then and have to be put back.
    /// </summary>
    internal static int TaskbarCreatedMessage { get; } = RegisterWindowMessage("TaskbarCreated");

    /// <summary>Puts the icon into the notification area.</summary>
    internal static bool Add(IntPtr window, int id, IntPtr icon, string tooltip)
    {
        NotifyIconData data = Describe(window, id, icon, tooltip);

        if (!Shell_NotifyIcon(NIM_ADD, ref data))
        {
            return false;
        }

        // The version is asked for after the icon is added and applies to it alone
        data.uVersion = NotifyIconVersion4;
        Shell_NotifyIcon(NIM_SETVERSION, ref data);

        return true;
    }

    /// <summary>Replaces the image and the tooltip of an icon already there.</summary>
    internal static bool Modify(IntPtr window, int id, IntPtr icon, string tooltip)
    {
        NotifyIconData data = Describe(window, id, icon, tooltip);
        return Shell_NotifyIcon(NIM_MODIFY, ref data);
    }

    /// <summary>Takes the icon away. A forgotten icon stays in the tray until hovered.</summary>
    internal static void Remove(IntPtr window, int id)
    {
        var data = new NotifyIconData
        {
            cbSize = Marshal.SizeOf<NotifyIconData>(),
            hWnd = window,
            uID = (uint)id,
        };

        Shell_NotifyIcon(NIM_DELETE, ref data);
    }

    /// <summary>
    /// The icon of the application at the size the tray asks for.
    /// </summary>
    /// <remarks>
    /// The image comes from the executable itself, so the tray shows what the user
    /// sees in Explorer. The build puts the icon under the standard resource; should
    /// it end up elsewhere, the first icon of the file is taken, and failing that —
    /// the icon Windows gives to an application without one. An icon is needed
    /// either way: without it the tray shows an empty spot.
    /// </remarks>
    internal static IntPtr LoadApplicationIcon()
    {
        int width = GetSystemMetrics(SM_CXSMICON);
        int height = GetSystemMetrics(SM_CYSMICON);

        IntPtr icon = LoadImage(
            GetModuleHandle(null), ApplicationIconResource, IMAGE_ICON, width, height, LR_DEFAULTCOLOR);

        if (icon == IntPtr.Zero && Environment.ProcessPath is { Length: > 0 } path)
        {
            icon = ExtractIconEx(path, 0, out IntPtr large, out IntPtr small, 1) > 0 ? small : IntPtr.Zero;

            if (large != IntPtr.Zero)
            {
                DestroyIcon(large);
            }
        }

        return icon != IntPtr.Zero ? icon : LoadIcon(IntPtr.Zero, ApplicationIconResource);
    }

    /// <summary>Releases an icon loaded by <see cref="LoadApplicationIcon"/>.</summary>
    internal static void ReleaseIcon(IntPtr icon)
    {
        if (icon != IntPtr.Zero)
        {
            DestroyIcon(icon);
        }
    }

    /// <summary>The notification the icon has sent: it sits in the low word of lParam.</summary>
    internal static int NotificationOf(IntPtr lParam) => (int)(lParam.ToInt64() & 0xFFFF);

    /// <summary>
    /// Brings the window to the foreground.
    /// </summary>
    /// <remarks>
    /// Windows takes a menu down when its owner window loses the foreground. A tray
    /// icon belongs to a window that is never shown, so the foreground has to be
    /// asked for by hand — otherwise the menu stays on screen after the user has
    /// clicked past it.
    /// </remarks>
    internal static void BringToForeground(IntPtr window) => SetForegroundWindow(window);

    private static NotifyIconData Describe(IntPtr window, int id, IntPtr icon, string tooltip) => new()
    {
        cbSize = Marshal.SizeOf<NotifyIconData>(),
        hWnd = window,
        uID = (uint)id,
        uFlags = NIF_MESSAGE | NIF_ICON | NIF_TIP | NIF_SHOWTIP,
        uCallbackMessage = CallbackMessage,
        hIcon = icon,
        szTip = tooltip,
    };

    [DllImport("shell32.dll", CharSet = CharSet.Unicode)]
    private static extern bool Shell_NotifyIcon(int dwMessage, ref NotifyIconData lpData);

    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    private static extern int RegisterWindowMessage(string lpString);

    [DllImport("user32.dll")]
    private static extern IntPtr LoadImage(IntPtr hInst, IntPtr name, uint type, int cx, int cy, uint fuLoad);

    private static IntPtr LoadImage(IntPtr hInst, int resource, uint type, int cx, int cy, uint fuLoad) =>
        LoadImage(hInst, new IntPtr(resource), type, cx, cy, fuLoad);

    [DllImport("user32.dll")]
    private static extern IntPtr LoadIcon(IntPtr hInstance, IntPtr lpIconName);

    private static IntPtr LoadIcon(IntPtr hInstance, int resource) =>
        LoadIcon(hInstance, new IntPtr(resource));

    [DllImport("shell32.dll", CharSet = CharSet.Unicode)]
    private static extern int ExtractIconEx(string lpszFile, int nIconIndex,
        out IntPtr phiconLarge, out IntPtr phiconSmall, int nIcons);

    [DllImport("user32.dll")]
    private static extern bool DestroyIcon(IntPtr hIcon);

    [DllImport("user32.dll")]
    private static extern int GetSystemMetrics(int nIndex);

    [DllImport("user32.dll")]
    private static extern bool SetForegroundWindow(IntPtr hWnd);

    [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
    private static extern IntPtr GetModuleHandle(string? lpModuleName);

    /// <summary>
    /// NOTIFYICONDATAW. The whole structure is described even though only its first
    /// half is used: Windows reads its size and refuses one it does not know.
    /// </summary>
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    private struct NotifyIconData
    {
        public int cbSize;
        public IntPtr hWnd;
        public uint uID;
        public uint uFlags;
        public int uCallbackMessage;
        public IntPtr hIcon;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
        public string szTip;

        public uint dwState;
        public uint dwStateMask;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
        public string szInfo;

        /// <summary>A timeout in the older versions and the protocol version here.</summary>
        public uint uVersion;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 64)]
        public string szInfoTitle;

        public uint dwInfoFlags;
        public Guid guidItem;
        public IntPtr hBalloonIcon;
    }
}