RemSound/src/RemSound.App/AsioLoadingSplash.cs

using System;
using System.Drawing;
using System.Threading;
using System.Windows.Forms;
using RemSound.Core;

namespace RemSound.App;

/// <summary>
/// A small "Loading audio driver..." window shown on its OWN dedicated UI thread while the
/// main thread builds <see cref="MainForm"/>.
///
/// Why it exists: opening an ASIO driver is slow — 1-3 seconds on many drivers — and that
/// happens synchronously during MainForm construction. Without a splash the user sees
/// nothing, or a blank "Not Responding" window shell, for those seconds, and it looks hung.
///
/// Why a SEPARATE thread: the ASIO driver must keep being opened on the main UI thread —
/// that is the STA, message-pumping thread every ASIO / COM driver is most compatible with,
/// and moving the driver open off it risks breaking drivers we cannot test. But the main
/// thread is therefore blocked for the whole open, so a splash shown on it would itself be
/// frozen. Running the splash on its own STA thread with its own message loop lets it paint
/// and stay alive while the main thread is busy. No ASIO or driver code is touched — only
/// this cosmetic window runs on the side thread.
///
/// Shown only for profiles that actually use an ASIO driver; a WASAPI-only profile builds
/// the main window near-instantly and gets no splash (it would just flash).
/// </summary>
internal sealed class AsioLoadingSplash
{
    private readonly Thread thread;
    private readonly ManualResetEventSlim shown = new(false);
    private volatile Form? form;

    private AsioLoadingSplash()
    {
        thread = new Thread(RunSplash)
        {
            IsBackground = true,
            Name = "RemSound startup splash",
        };
        thread.SetApartmentState(ApartmentState.STA);
        thread.Start();
        // Wait (briefly, capped) for the window to actually be on screen before the caller
        // begins the slow ASIO work — so the user sees the splash, not a blank moment. The
        // cap means a splash hiccup can never stall startup.
        shown.Wait(TimeSpan.FromSeconds(2));
    }

    /// <summary>
    /// Starts the splash only when <paramref name="profile"/> has an ASIO driver selected —
    /// the only case where MainForm construction is slow. Returns null for WASAPI-only
    /// profiles. Dismiss the returned handle once the main window has been built.
    /// </summary>
    public static AsioLoadingSplash? StartIfNeeded(Profile? profile)
    {
        if (string.IsNullOrWhiteSpace(profile?.AsioDriverName)) return null;
        try
        {
            return new AsioLoadingSplash();
        }
        catch
        {
            // The splash is purely cosmetic — if it can't even be created, let the app
            // start silently rather than have a splash failure block launch.
            return null;
        }
    }

    private void RunSplash()
    {
        try
        {
            using var splash = new Form
            {
                Text = "RemSound",
                FormBorderStyle = FormBorderStyle.FixedDialog,
                StartPosition = FormStartPosition.CenterScreen,
                ControlBox = false,
                MinimizeBox = false,
                MaximizeBox = false,
                ShowInTaskbar = false,
                TopMost = true,
                ClientSize = new Size(380, 96),
                AccessibleName = "RemSound is starting",
            };
            splash.Controls.Add(new Label
            {
                Dock = DockStyle.Fill,
                TextAlign = ContentAlignment.MiddleCenter,
                Text = "Loading audio driver, please wait...",
                AccessibleName = "Loading audio driver, please wait",
            });
            splash.Shown += (_, _) => shown.Set();
            form = splash;
            Application.Run(splash);
        }
        catch
        {
            // Never let a splash failure escape on its own thread.
        }
        finally
        {
            // Unblock the constructor even if the window never managed to show.
            shown.Set();
        }
    }

    /// <summary>
    /// Closes the splash. Call from the main thread once <see cref="MainForm"/> has been
    /// constructed. Fire-and-forget — the splash's own background thread tears itself down.
    /// </summary>
    public void Dismiss()
    {
        try
        {
            shown.Set();
            var f = form;
            if (f is not null && f.IsHandleCreated && !f.IsDisposed)
            {
                f.BeginInvoke(() =>
                {
                    try { f.Close(); }
                    catch { /* already gone */ }
                });
            }
        }
        catch
        {
            // Cosmetic teardown — never throw into the startup path.
        }
    }
}