windows/Media/MediaService.cs

using Windows.Media.Control;

namespace MusicBridge.Agent.Media;

internal sealed class MediaService : IMediaService, IDisposable
{
    private readonly GlobalSystemMediaTransportControlsSessionManager manager;
    private GlobalSystemMediaTransportControlsSession? observed;
    private GlobalSystemMediaTransportControlsSessionMediaProperties? metadata;
    private readonly ArtworkCache artwork = new();
    private long metadataRevision;
    private long loadedRevision = -1;
    private DateTimeOffset nextMetadataRefresh;
    private string? artworkError;
    private bool disposed;
    public event Action? Changed;
    public Artwork? GetArtwork(string id) => artwork.Get(id);

    public MediaService(GlobalSystemMediaTransportControlsSessionManager manager)
    {
        this.manager = manager;
        manager.CurrentSessionChanged += OnCurrentSessionChanged;
        manager.SessionsChanged += OnSessionsChanged;
    }

    // Console commands and remote clients must not race each other.
    private readonly SemaphoreSlim gate = new(1, 1);

    public async Task<MediaState> ReadAsync(CancellationToken cancellationToken)
    {
        await gate.WaitAsync(cancellationToken);
        try
        {
            var state = new MediaState();
            try
            {
                var session = manager.GetCurrentSession();
                Observe(session);
                if (session is not null)
                {
                    var revision = Interlocked.Read(ref metadataRevision);
                    if (metadata is null || loadedRevision != revision || DateTimeOffset.UtcNow >= nextMetadataRefresh)
                    {
                        metadata = null;
                        artwork.Clear();
                        metadata = await session.TryGetMediaPropertiesAsync().AsTask(cancellationToken);
                        await LoadArtworkAsync(metadata, cancellationToken);
                        loadedRevision = revision; // Events during this read remain dirty for the next read.
                        nextMetadataRefresh = DateTimeOffset.UtcNow.AddSeconds(10);
                    }
                    var media = metadata;
                    var playback = session.GetPlaybackInfo();
                    var timeline = session.GetTimelineProperties();
                    var range = GetSeekRange(timeline);
                    var c = playback.Controls;
                    state = state with
                    {
                        HasSession = true, Title = media.Title, Artist = media.Artist,
                        Source = session.SourceAppUserModelId,
                        ArtworkId = artwork.Current?.Id, ArtworkError = artworkError,
                        PlaybackStatus = playback.PlaybackStatus.ToString(),
                        PositionSeconds = GetPosition(timeline, playback),
                        StartSeconds = timeline.StartTime.TotalSeconds, EndSeconds = timeline.EndTime.TotalSeconds,
                        MinSeekSeconds = range.Min, MaxSeekSeconds = range.Max,
                        PlaybackRate = double.IsFinite(playback.PlaybackRate ?? 1) ? playback.PlaybackRate ?? 1 : 1,
                        Capabilities = new(c.IsPlayEnabled, c.IsPauseEnabled, c.IsPlayPauseToggleEnabled,
                            c.IsNextEnabled, c.IsPreviousEnabled, c.IsPlaybackPositionEnabled && range.Max > range.Min)
                    };
                }
            }
            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested) { throw; }
            catch (Exception ex)
            {
                metadata = null;
                artwork.Clear();
                state = state with { MediaError = ex.Message };
            }
            try
            {
                var volume = SystemVolume.Read();
                state = state with { Volume = volume.Level, Muted = volume.Muted };
            }
            catch (Exception ex) { state = state with { VolumeError = ex.Message }; }
            return state with { Timestamp = DateTimeOffset.UtcNow };
        }
        finally { gate.Release(); }
    }

    public async Task<CommandResult> ExecuteAsync(MediaCommand command, CancellationToken cancellationToken)
    {
        var invalid = CommandValidation.Validate(command);
        if (invalid is not null) return invalid with { Id = command.Id };
        await gate.WaitAsync(cancellationToken);
        try
        {
            return (await ExecuteCoreAsync(command)) with { Id = command.Id };
        }
        catch (Exception ex)
        {
            return new(false, "operation_failed", ex.Message, command.Id);
        }
        finally { gate.Release(); Changed?.Invoke(); }
    }

    private async Task LoadArtworkAsync(GlobalSystemMediaTransportControlsSessionMediaProperties properties, CancellationToken cancellationToken)
    {
        artworkError = null;
        if (properties.Thumbnail is null) return;
        using var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        timeout.CancelAfter(TimeSpan.FromSeconds(2));
        try
        {
            using var source = await properties.Thumbnail.OpenReadAsync().AsTask(timeout.Token);
            if (source.Size > ArtworkCache.MaxBytes) throw new InvalidDataException("Обложка больше 2 МиБ.");
            using var stream = source.AsStreamForRead();
            await artwork.LoadAsync(stream, timeout.Token);
        }
        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested) { throw; }
        catch (OperationCanceledException) { artworkError = "Время чтения обложки истекло."; }
        catch (Exception ex) { artworkError = ex.Message; }
    }

    // Event callbacks only invalidate/notify; WinRT reads run under the shared gate.
    private void OnCurrentSessionChanged(GlobalSystemMediaTransportControlsSessionManager sender, CurrentSessionChangedEventArgs args) => Invalidate();
    private void OnSessionsChanged(GlobalSystemMediaTransportControlsSessionManager sender, SessionsChangedEventArgs args) => Invalidate();
    private void OnMediaChanged(GlobalSystemMediaTransportControlsSession sender, MediaPropertiesChangedEventArgs args) => Invalidate();
    private void OnPlaybackChanged(GlobalSystemMediaTransportControlsSession sender, PlaybackInfoChangedEventArgs args) => Changed?.Invoke();
    private void OnTimelineChanged(GlobalSystemMediaTransportControlsSession sender, TimelinePropertiesChangedEventArgs args) => Changed?.Invoke();
    private void Invalidate() { Interlocked.Increment(ref metadataRevision); Changed?.Invoke(); }

    private void Observe(GlobalSystemMediaTransportControlsSession? session)
    {
        if (ReferenceEquals(observed, session)) return;
        if (observed is not null)
        {
            observed.MediaPropertiesChanged -= OnMediaChanged;
            observed.PlaybackInfoChanged -= OnPlaybackChanged;
            observed.TimelinePropertiesChanged -= OnTimelineChanged;
        }
        observed = session;
        metadata = null;
        artwork.Clear();
        artworkError = null;
        if (observed is not null)
        {
            observed.MediaPropertiesChanged += OnMediaChanged;
            observed.PlaybackInfoChanged += OnPlaybackChanged;
            observed.TimelinePropertiesChanged += OnTimelineChanged;
        }
    }

    public void Dispose()
    {
        if (disposed) return;
        disposed = true;
        manager.CurrentSessionChanged -= OnCurrentSessionChanged;
        manager.SessionsChanged -= OnSessionsChanged;
        Observe(null);
        // Owner stops server/read loop before disposing the media service.
        Changed = null;
        gate.Dispose();
    }

    private async Task<CommandResult> ExecuteCoreAsync(MediaCommand command)
    {
        switch (command.Type)
        {
            case "volume": SystemVolume.Set((float)command.Value!.Value); return Ok();
            case "volumeRelative": SystemVolume.Change((float)command.Value!.Value); return Ok();
            case "toggleMute": SystemVolume.ToggleMute(); return Ok();
        }
        var session = manager.GetCurrentSession();
        if (session is null) return CommandValidation.Error("no_session", "Медиаплеер не найден.");
        var playback = session.GetPlaybackInfo();
        var controls = playback.Controls;
        bool accepted;
        switch (command.Type)
        {
            case "play":
                if (!controls.IsPlayEnabled) return Unsupported();
                accepted = await session.TryPlayAsync(); break;
            case "pause":
                if (!controls.IsPauseEnabled) return Unsupported();
                accepted = await session.TryPauseAsync(); break;
            case "toggle":
                if (!controls.IsPlayPauseToggleEnabled) return Unsupported();
                accepted = await session.TryTogglePlayPauseAsync(); break;
            case "next":
                if (!controls.IsNextEnabled) return Unsupported();
                accepted = await session.TrySkipNextAsync(); break;
            case "previous":
                if (!controls.IsPreviousEnabled) return Unsupported();
                accepted = await session.TrySkipPreviousAsync(); break;
            default:
                if (!controls.IsPlaybackPositionEnabled) return Unsupported();
                var timeline = session.GetTimelineProperties();
                var range = GetSeekRange(timeline);
                if (range.Max <= range.Min) return Unsupported();
                var target = command.Value!.Value;
                if (command.Type == "seekRelative") target += GetPosition(timeline, playback);
                target = Math.Clamp(target, range.Min, range.Max);
                accepted = await session.TryChangePlaybackPositionAsync(TimeSpan.FromSeconds(target).Ticks);
                break;
        }
        return accepted ? Ok() : CommandValidation.Error("rejected", "Плеер отклонил команду.");
    }

    private static CommandResult Ok() => new(true, "ok", "Команда выполнена.");
    private static CommandResult Unsupported() => CommandValidation.Error("unsupported", "Команда сейчас недоступна у плеера.");
    private static (double Min, double Max) GetSeekRange(GlobalSystemMediaTransportControlsSessionTimelineProperties t)
        => TimelineMath.SeekRange(t.StartTime.TotalSeconds, t.EndTime.TotalSeconds, t.MinSeekTime.TotalSeconds, t.MaxSeekTime.TotalSeconds);
    private static double GetPosition(GlobalSystemMediaTransportControlsSessionTimelineProperties t,
        GlobalSystemMediaTransportControlsSessionPlaybackInfo p) => TimelineMath.Position(t.Position.TotalSeconds,
            t.StartTime.TotalSeconds, t.EndTime.TotalSeconds,
            p.PlaybackStatus == GlobalSystemMediaTransportControlsSessionPlaybackStatus.Playing,
            t.LastUpdatedTime, DateTimeOffset.UtcNow, p.PlaybackRate ?? 1);
}