ersatztv/ErsatzTV.Application/MediaCollections/Commands/UpdateCollectionHandler.cs

using System.Threading.Channels;
using ErsatzTV.Application.Playouts;
using ErsatzTV.Core;
using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Errors;
using ErsatzTV.Core.Interfaces.Repositories;
using ErsatzTV.Core.Interfaces.Search;
using ErsatzTV.Core.Scheduling;
using ErsatzTV.Infrastructure.Data;
using ErsatzTV.Infrastructure.Extensions;
using Microsoft.EntityFrameworkCore;

namespace ErsatzTV.Application.MediaCollections;

public class UpdateCollectionHandler : IRequestHandler<UpdateCollection, Either<BaseError, Unit>>
{
    private readonly ChannelWriter<IBackgroundServiceRequest> _channel;
    private readonly IDbContextFactory<TvContext> _dbContextFactory;
    private readonly IMediaCollectionRepository _mediaCollectionRepository;
    private readonly ISearchTargets _searchTargets;

    public UpdateCollectionHandler(
        IDbContextFactory<TvContext> dbContextFactory,
        IMediaCollectionRepository mediaCollectionRepository,
        ChannelWriter<IBackgroundServiceRequest> channel,
        ISearchTargets searchTargets)
    {
        _dbContextFactory = dbContextFactory;
        _mediaCollectionRepository = mediaCollectionRepository;
        _channel = channel;
        _searchTargets = searchTargets;
    }

    public async Task<Either<BaseError, Unit>> Handle(
        UpdateCollection request,
        CancellationToken cancellationToken)
    {
        await using TvContext dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
        Option<Collection> maybeCollection = await CollectionMustExist(dbContext, request, cancellationToken);
        return await maybeCollection.Match(
            Some: async collection =>
            {
                Validation<BaseError, Collection> validation = await Validate(dbContext, request, collection);
                return await validation.Apply(c => ApplyUpdateRequest(dbContext, c, request, cancellationToken));
            },
            None: () => Task.FromResult<Either<BaseError, Unit>>(
                new NotFoundError($"Collection {request.CollectionId} does not exist.")));
    }

    private async Task<Unit> ApplyUpdateRequest(
        TvContext dbContext,
        Collection c,
        UpdateCollection request,
        CancellationToken cancellationToken)
    {
        c.Name = request.Name;
        foreach (bool useCustomPlaybackOrder in request.UseCustomPlaybackOrder)
        {
            c.UseCustomPlaybackOrder = useCustomPlaybackOrder;
        }

        // Only rotate the ETag when the name/flag actually changed — a no-op re-submit must not bump the
        // Version (spurious rebuilds / editor invalidation) — #269. When it did change, force-write past a
        // concurrent bump from the custom-order editor (this writer takes no If-Match, so a benign race
        // must not 500) — #253/#269 §7a.
        if (dbContext.ChangeTracker.HasChanges())
        {
            c.Version++;
            await dbContext.SaveChangesForcingVersion(cancellationToken);

            if (request.UseCustomPlaybackOrder.IsSome)
            {
                // post-commit side effect runs on CancellationToken.None so a late request cancellation
                // can't abort it after the commit landed (#254)
                // refresh all playouts that use this collection
                foreach (int playoutId in await _mediaCollectionRepository.PlayoutIdsUsingCollection(
                             request.CollectionId))
                {
                    await _channel.WriteAsync(new BuildPlayout(playoutId, PlayoutBuildMode.Refresh), CancellationToken.None);
                }
            }
        }

        _searchTargets.SearchTargetsChanged();

        return Unit.Default;
    }

    private static async Task<Validation<BaseError, Collection>> Validate(
        TvContext dbContext,
        UpdateCollection request,
        Collection collection) =>
        (await ValidateName(dbContext, request)).Map(_ => collection);

    private static Task<Option<Collection>> CollectionMustExist(
        TvContext dbContext,
        UpdateCollection updateCollection,
        CancellationToken cancellationToken) =>
        dbContext.Collections
            .SelectOneAsync(c => c.Id, c => c.Id == updateCollection.CollectionId, cancellationToken)
            .Map(identity);

    private static async Task<Validation<BaseError, string>> ValidateName(
        TvContext dbContext,
        UpdateCollection updateCollection)
    {
        Validation<BaseError, string> result1 = updateCollection.NotEmpty(c => c.Name)
            .Bind(_ => updateCollection.NotLongerThan(50)(c => c.Name));

        bool duplicateName = await dbContext.Collections
            .AnyAsync(c => c.Id != updateCollection.CollectionId && c.Name == updateCollection.Name);

        Validation<BaseError, Unit> result2 = duplicateName
            ? Fail<BaseError, Unit>("Collection name must be unique")
            : Success<BaseError, Unit>(Unit.Default);

        return (result1, result2).Apply((_, _) => updateCollection.Name);
    }
}