PLib/src/PLib.Desktop/Controls/VlcVideoView.cs

using Avalonia;
using Avalonia.Controls;
using Avalonia.Platform;
using Avalonia.Threading;
using LibVLCSharp.Shared;

namespace PLib.Desktop.Controls;

/// <summary>
/// A video surface backed by LibVLC.
/// </summary>
/// <remarks>
/// VLC draws straight into a native child window that Avalonia creates for us, so no frame
/// ever crosses into managed memory — playback costs what the decoder costs and nothing more.
/// The price is airspace: this region is a separate window on top of the Avalonia surface, so
/// nothing can be drawn over the picture. The media page keeps its controls beside the video
/// rather than on it for exactly that reason.
/// <para>
/// The property surface deliberately mirrors what a media control is expected to expose —
/// source, position, duration, volume — so the page binds to it the same way it would to any
/// other player.
/// </para>
/// </remarks>
public sealed class VlcVideoView : NativeControlHost
{
    public static readonly StyledProperty<Uri?> SourceProperty =
        AvaloniaProperty.Register<VlcVideoView, Uri?>(nameof(Source));

    public static readonly StyledProperty<bool> AutoPlayProperty =
        AvaloniaProperty.Register<VlcVideoView, bool>(nameof(AutoPlay), defaultValue: true);

    public static readonly StyledProperty<TimeSpan> PositionProperty =
        AvaloniaProperty.Register<VlcVideoView, TimeSpan>(nameof(Position));

    public static readonly StyledProperty<TimeSpan> DurationProperty =
        AvaloniaProperty.Register<VlcVideoView, TimeSpan>(nameof(Duration));

    public static readonly StyledProperty<bool> IsPlayingProperty =
        AvaloniaProperty.Register<VlcVideoView, bool>(nameof(IsPlaying));

    public static readonly StyledProperty<bool> IsMutedProperty =
        AvaloniaProperty.Register<VlcVideoView, bool>(nameof(IsMuted));

    /// <summary>Volume as a fraction; LibVLC works in percent and is converted on the way in.</summary>
    public static readonly StyledProperty<double> VolumeProperty =
        AvaloniaProperty.Register<VlcVideoView, double>(nameof(Volume), defaultValue: 0.8);

    public static readonly StyledProperty<string?> LastErrorProperty =
        AvaloniaProperty.Register<VlcVideoView, string?>(nameof(LastError));

    private MediaPlayer? _player;

    /// <summary>
    /// True once VLC has been handed the native window. Playback cannot start before that,
    /// or VLC opens a top-level window of its own.
    /// </summary>
    private bool _surfaceReady;

    public Uri? Source
    {
        get => GetValue(SourceProperty);
        set => SetValue(SourceProperty, value);
    }

    public bool AutoPlay
    {
        get => GetValue(AutoPlayProperty);
        set => SetValue(AutoPlayProperty, value);
    }

    public TimeSpan Position
    {
        get => GetValue(PositionProperty);
        private set => SetValue(PositionProperty, value);
    }

    public TimeSpan Duration
    {
        get => GetValue(DurationProperty);
        private set => SetValue(DurationProperty, value);
    }

    public bool IsPlaying
    {
        get => GetValue(IsPlayingProperty);
        private set => SetValue(IsPlayingProperty, value);
    }

    public bool IsMuted
    {
        get => GetValue(IsMutedProperty);
        set => SetValue(IsMutedProperty, value);
    }

    public double Volume
    {
        get => GetValue(VolumeProperty);
        set => SetValue(VolumeProperty, value);
    }

    public string? LastError
    {
        get => GetValue(LastErrorProperty);
        private set => SetValue(LastErrorProperty, value);
    }

    public void Play()
    {
        if (_player is null)
        {
            return;
        }

        if (_player.Media is not null)
        {
            _player.Play();
        }
        else
        {
            OpenCurrentSource();
        }
    }

    public void Pause() => _player?.SetPause(true);

    public void Stop() => _player?.Stop();

    public void Seek(TimeSpan position)
    {
        if (_player is { IsSeekable: true })
        {
            _player.Time = (long)position.TotalMilliseconds;
        }
    }

    protected override IPlatformHandle CreateNativeControlCore(IPlatformHandle parent)
    {
        // Avalonia gives us an empty child window of the right platform kind; VLC renders
        // into it once we hand over the handle.
        var handle = base.CreateNativeControlCore(parent);

        _player = new MediaPlayer(VlcRuntime.Shared);
        AttachPlayerEvents(_player);

        if (OperatingSystem.IsWindows())
        {
            _player.Hwnd = handle.Handle;
        }
        else if (OperatingSystem.IsLinux())
        {
            _player.XWindow = (uint)handle.Handle;
        }
        else if (OperatingSystem.IsMacOS())
        {
            _player.NsObject = handle.Handle;
        }

        _player.Mute = IsMuted;
        _player.Volume = ToVlcVolume(Volume);
        _surfaceReady = true;

        if (AutoPlay)
        {
            OpenCurrentSource();
        }

        return handle;
    }

    protected override void DestroyNativeControlCore(IPlatformHandle control)
    {
        // Tear the player down before the window it draws into disappears.
        if (_player is { } player)
        {
            _player = null;
            _surfaceReady = false;

            DetachPlayerEvents(player);
            player.Stop();
            player.Dispose();
        }

        base.DestroyNativeControlCore(control);
    }

    protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
    {
        base.OnPropertyChanged(change);

        if (_player is not { } player)
        {
            return;
        }

        if (change.Property == SourceProperty)
        {
            OpenCurrentSource();
        }
        else if (change.Property == VolumeProperty)
        {
            player.Volume = ToVlcVolume(Volume);
        }
        else if (change.Property == IsMutedProperty)
        {
            player.Mute = IsMuted;
        }
    }

    private void OpenCurrentSource()
    {
        if (!_surfaceReady || _player is not { } player || Source is not { } source)
        {
            return;
        }

        try
        {
            LastError = null;

            // The media object only has to survive the call: VLC takes its own reference.
            using var media = new Media(VlcRuntime.Shared, source);

            if (!player.Play(media))
            {
                LastError = "VLC не смог открыть файл";
            }
        }
        catch (Exception ex)
        {
            LastError = ex.Message;
        }
    }

    private void AttachPlayerEvents(MediaPlayer player)
    {
        player.TimeChanged += OnTimeChanged;
        player.LengthChanged += OnLengthChanged;
        player.Playing += OnPlaying;
        player.Paused += OnStoppedPlaying;
        player.Stopped += OnStoppedPlaying;
        player.EndReached += OnStoppedPlaying;
        player.EncounteredError += OnEncounteredError;
    }

    private void DetachPlayerEvents(MediaPlayer player)
    {
        player.TimeChanged -= OnTimeChanged;
        player.LengthChanged -= OnLengthChanged;
        player.Playing -= OnPlaying;
        player.Paused -= OnStoppedPlaying;
        player.Stopped -= OnStoppedPlaying;
        player.EndReached -= OnStoppedPlaying;
        player.EncounteredError -= OnEncounteredError;
    }

    // Every VLC event arrives on one of its own threads, so nothing here may touch an
    // Avalonia property directly.
    private void OnTimeChanged(object? sender, MediaPlayerTimeChangedEventArgs e) =>
        Post(() => Position = TimeSpan.FromMilliseconds(Math.Max(0, e.Time)));

    private void OnLengthChanged(object? sender, MediaPlayerLengthChangedEventArgs e) =>
        Post(() => Duration = TimeSpan.FromMilliseconds(Math.Max(0, e.Length)));

    private void OnPlaying(object? sender, EventArgs e) => Post(() => IsPlaying = true);

    private void OnStoppedPlaying(object? sender, EventArgs e) => Post(() => IsPlaying = false);

    private void OnEncounteredError(object? sender, EventArgs e) =>
        Post(() => LastError = "VLC сообщил об ошибке воспроизведения");

    private static void Post(Action action) => Dispatcher.UIThread.Post(action, DispatcherPriority.Background);

    private static int ToVlcVolume(double volume) => (int)Math.Round(Math.Clamp(volume, 0, 1) * 100);
}