Terminal.Gui/Terminal.Gui/App/MainLoop/ApplicationMainLoop.cs

using System.Collections.Concurrent;
using System.Diagnostics;

namespace Terminal.Gui.App;

/// <summary>
///     The main application loop that runs Terminal.Gui's UI rendering and event processing.
/// </summary>
/// <remarks>
///     This class coordinates the Terminal.Gui application lifecycle by:
///     <list type="bullet">
///         <item>Processing buffered input events and translating them to UI events</item>
///         <item>Executing user timeout callbacks at scheduled intervals</item>
///         <item>Detecting which views need redrawing or layout updates</item>
///         <item>Rendering UI changes to the console output buffer</item>
///         <item>Managing cursor position and visibility</item>
///         <item>Throttling iterations to respect <see cref="Application.MaximumIterationsPerSecond"/></item>
///     </list>
/// </remarks>
/// <typeparam name="TInputRecord">Type of raw input events, e.g. <see cref="ConsoleKeyInfo"/> for .NET driver</typeparam>
public class ApplicationMainLoop<TInputRecord> : IApplicationMainLoop<TInputRecord> where TInputRecord : struct
{
    private ITimedEvents? _timedEvents;
    private ConcurrentQueue<TInputRecord>? _inputQueue;
    private IInputProcessor? _inputProcessor;
    private IOutput? _output;
    private AnsiRequestScheduler? _ansiRequestScheduler;
    private ISizeMonitor? _sizeMonitor;

    /// <inheritdoc/>
    public IApplication? App { get; private set; }

    /// <inheritdoc/>
    public ITimedEvents TimedEvents
    {
        get => _timedEvents ?? throw new NotInitializedException (nameof (TimedEvents));
        private set => _timedEvents = value;
    }

    // TODO: follow above pattern for others too

    /// <summary>
    ///     The input events thread-safe collection. This is populated on separate
    ///     thread by a <see cref="IInput{T}"/>. Is drained as part of each
    ///     <see cref="Iteration"/> on the main loop thread.
    /// </summary>
    public ConcurrentQueue<TInputRecord> InputQueue
    {
        get => _inputQueue ?? throw new NotInitializedException (nameof (InputQueue));
        private set => _inputQueue = value;
    }

    /// <inheritdoc/>
    public IInputProcessor InputProcessor
    {
        get => _inputProcessor ?? throw new NotInitializedException (nameof (InputProcessor));
        private set => _inputProcessor = value;
    }

    /// <inheritdoc/>
    public IOutputBuffer OutputBuffer { get; } = new OutputBufferImpl ();

    /// <inheritdoc/>
    public IOutput Output
    {
        get => _output ?? throw new NotInitializedException (nameof (Output));
        private set => _output = value;
    }

    /// <inheritdoc/>
    public AnsiRequestScheduler AnsiRequestScheduler
    {
        get => _ansiRequestScheduler ?? throw new NotInitializedException (nameof (AnsiRequestScheduler));
        private set => _ansiRequestScheduler = value;
    }

    /// <inheritdoc/>
    public ISizeMonitor SizeMonitor
    {
        get => _sizeMonitor ?? throw new NotInitializedException (nameof (SizeMonitor));
        private set => _sizeMonitor = value;
    }

    /// <summary>
    ///     Initializes the class with the provided subcomponents
    /// </summary>
    /// <param name="timedEvents"></param>
    /// <param name="inputBuffer"></param>
    /// <param name="inputProcessor"></param>
    /// <param name="consoleOutput"></param>
    /// <param name="componentFactory"></param>
    /// <param name="app"></param>
    public void Initialize (
        ITimedEvents timedEvents,
        ConcurrentQueue<TInputRecord> inputBuffer,
        IInputProcessor inputProcessor,
        IOutput consoleOutput,
        IComponentFactory<TInputRecord> componentFactory,
        IApplication? app
    )
    {
        App = app;
        InputQueue = inputBuffer;
        Output = consoleOutput;
        InputProcessor = inputProcessor;

        TimedEvents = timedEvents;
        AnsiRequestScheduler = new (InputProcessor.GetParser ());

        OutputBuffer.SetSize (consoleOutput.GetSize ().Width, consoleOutput.GetSize ().Height);
        SizeMonitor = componentFactory.CreateSizeMonitor (Output, OutputBuffer);
    }

    /// <inheritdoc/>
    public void Iteration ()
    {
        App?.RaiseIteration ();

        DateTime dt = DateTime.Now;
        int timeAllowed = 1000 / Math.Max (1, (int)Application.MaximumIterationsPerSecond);

        IterationImpl ();

        TimeSpan took = DateTime.Now - dt;
        TimeSpan sleepFor = TimeSpan.FromMilliseconds (timeAllowed) - took;

        Logging.TotalIterationMetric.Record (took.Milliseconds);

        if (sleepFor.Milliseconds > 0)
        {
            Task.Delay (sleepFor).Wait ();
        }
    }

    internal void IterationImpl ()
    {
        // Pull any input events from the input queue and process them
        InputProcessor.ProcessQueue ();

        if (App?.TopRunnableView != null)
        {
            bool needsDrawOrLayout = AnySubViewsNeedDrawn (App?.Popover?.GetActivePopover () as View)
                                     || AnySubViewsNeedDrawn (App?.TopRunnableView)
                                     || (App?.Mouse.MouseGrabView != null && AnySubViewsNeedDrawn (App?.Mouse.MouseGrabView));

            SizeMonitor.Poll ();

            if (needsDrawOrLayout)
            {
                Logging.Redraws.Add (1);

                App?.LayoutAndDraw (forceRedraw: false);

                Output.Write (OutputBuffer);
            }

            SetCursor ();
        }

        var swCallbacks = Stopwatch.StartNew ();

        TimedEvents.RunTimers ();

        Logging.IterationInvokesAndTimeouts.Record (swCallbacks.Elapsed.Milliseconds);
    }

    private void SetCursor ()
    {
        View? mostFocused = App?.TopRunnableView!.MostFocused;

        if (mostFocused == null)
        {
            return;
        }

        Point? to = mostFocused.PositionCursor ();

        if (to.HasValue)
        {
            // Translate to screen coordinates
            to = mostFocused.ViewportToScreen (to.Value);

            Output.SetCursorPosition (to.Value.X, to.Value.Y);
            Output.SetCursorVisibility (mostFocused.CursorVisibility);
        }
        else
        {
            Output.SetCursorVisibility (CursorVisibility.Invisible);
        }
    }

    private bool AnySubViewsNeedDrawn (View? v)
    {
        if (v is null)
        {
            return false;
        }

        if (v.NeedsDraw || v.NeedsLayout)
        {
            // Logging.Trace ($"{v.GetType ().Name} triggered redraw (NeedsDraw={v.NeedsDraw} NeedsLayout={v.NeedsLayout}) ");

            return true;
        }

        foreach (View subview in v.SubViews)
        {
            if (AnySubViewsNeedDrawn (subview))
            {
                return true;
            }
        }

        return false;
    }

    /// <inheritdoc/>
    public void Dispose ()
    {
        // TODO release managed resources here
    }
}