ersatztv/ErsatzTV.Application/Libraries/Commands/QueueLibraryScanByLibraryIdHandler.cs

using System.Threading.Channels;
using ErsatzTV.Application.Emby;
using ErsatzTV.Application.Jellyfin;
using ErsatzTV.Application.MediaSources;
using ErsatzTV.Application.Plex;
using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Interfaces.Locking;
using ErsatzTV.Infrastructure.Data;
using ErsatzTV.Infrastructure.Extensions;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;

namespace ErsatzTV.Application.Libraries;

public class QueueLibraryScanByLibraryIdHandler(
    IDbContextFactory<TvContext> dbContextFactory,
    IEntityLocker locker,
    ChannelWriter<IScannerBackgroundServiceRequest> scannerWorker,
    ILogger<QueueLibraryScanByLibraryIdHandler> logger)
    : IRequestHandler<QueueLibraryScanByLibraryId, QueueLibraryScanResult>
{
    public async Task<QueueLibraryScanResult> Handle(
        QueueLibraryScanByLibraryId request,
        CancellationToken cancellationToken)
    {
        await using TvContext dbContext = await dbContextFactory.CreateDbContextAsync(cancellationToken);

        Option<Library> maybeLibrary = await dbContext.Libraries
            .AsNoTracking()
            .SelectOneAsync(l => l.Id, l => l.Id == request.LibraryId, cancellationToken);

        foreach (Library library in maybeLibrary)
        {
            bool shouldSyncItems = library switch
            {
                PlexLibrary plexLibrary => plexLibrary.ShouldSyncItems,
                JellyfinLibrary jellyfinLibrary => jellyfinLibrary.ShouldSyncItems,
                EmbyLibrary embyLibrary => embyLibrary.ShouldSyncItems,
                _ => true
            };

            if (!shouldSyncItems)
            {
                logger.LogWarning("Library sync is disabled for library id {Id}", library.Id);
                return QueueLibraryScanResult.SyncDisabled;
            }

            // A true from LockLibrary confers ownership of exactly one release; a false means a scan
            // is already in progress and we own no release.
            if (!locker.LockLibrary(library.Id))
            {
                return QueueLibraryScanResult.AlreadyScanning;
            }

            try
            {
                logger.LogDebug("Queued library scan for library id {Id}", library.Id);

                switch (library)
                {
                    case LocalLibrary:
                        await scannerWorker.WriteAsync(new ForceScanLocalLibrary(library.Id), cancellationToken);
                        break;
                    case PlexLibrary:
                        await scannerWorker.WriteAsync(
                            new SynchronizePlexLibraries(library.MediaSourceId),
                            cancellationToken);
                        await scannerWorker.WriteAsync(
                            new ForceSynchronizePlexLibraryById(library.Id, false),
                            cancellationToken);
                        break;
                    case JellyfinLibrary:
                        await scannerWorker.WriteAsync(
                            new SynchronizeJellyfinLibraries(library.MediaSourceId),
                            cancellationToken);
                        await scannerWorker.WriteAsync(
                            new ForceSynchronizeJellyfinLibraryById(library.Id, false),
                            cancellationToken);
                        break;
                    case EmbyLibrary:
                        await scannerWorker.WriteAsync(
                            new SynchronizeEmbyLibraries(library.MediaSourceId),
                            cancellationToken);
                        await scannerWorker.WriteAsync(
                            new ForceSynchronizeEmbyLibraryById(library.Id, false),
                            cancellationToken);
                        break;
                }
            }
            catch
            {
                // the scanner only unlocks when it receives the message; if enqueueing fails
                // (e.g. request aborted / channel completed) after we acquired the lock, release
                // it here or it is held forever (EnqueueWithTraktLock pattern).
                locker.UnlockLibrary(library.Id);
                throw;
            }

            return QueueLibraryScanResult.Queued;
        }

        return QueueLibraryScanResult.NotFound;
    }
}