ersatztv/ErsatzTV.Application/Playouts/Commands/TimeShiftOnDemandPlayoutHandler.cs

using System.Threading.Channels;
using ErsatzTV.Application.Channels;
using ErsatzTV.Core;
using ErsatzTV.Core.Interfaces.Scheduling;

namespace ErsatzTV.Application.Playouts;

public class TimeShiftOnDemandPlayoutHandler(
    IPlayoutTimeShifter playoutTimeShifter,
    ChannelWriter<IBackgroundServiceRequest> workerChannel)
    : IRequestHandler<TimeShiftOnDemandPlayout, Option<BaseError>>
{
    public async Task<Option<BaseError>> Handle(TimeShiftOnDemandPlayout request, CancellationToken cancellationToken)
    {
        try
        {
            List<string> staleGuideChannels = await playoutTimeShifter.TimeShift(
                request.PlayoutId,
                request.Now,
                request.Force,
                cancellationToken);

            // the time shift rewrote stored PlayoutItem timestamps but not the cached XMLTV
            // fragment; rebuild the guide for the shifted channel (and any mirrors of it) so a
            // client tuning in doesn't see a stale timeline. this is a post-commit side effect
            // (TimeShift already saved) so it runs on CancellationToken.None — a session token that
            // cancels between the DB commit and this enqueue must not leave the guide stale
            // (decisions.md api.postcommit-cancellation-none)
            foreach (string channelNumber in staleGuideChannels)
            {
                await workerChannel.WriteAsync(new RefreshChannelData(channelNumber), CancellationToken.None);
            }
        }
        catch (Exception ex)
        {
            return BaseError.New(ex.Message);
        }

        return Option<BaseError>.None;
    }
}