using System.Threading.Channels;
using ErsatzTV.Application.Channels;
using ErsatzTV.Core;
using ErsatzTV.Core.Domain;
using ErsatzTV.Infrastructure.Data;
using ErsatzTV.Infrastructure.Extensions;
using Microsoft.EntityFrameworkCore;

namespace ErsatzTV.Application.Playouts;

public class
    UpdateExternalJsonPlayoutHandler : IRequestHandler<UpdateExternalJsonPlayout,
    Either<BaseError, PlayoutNameViewModel>>
{
    private readonly IDbContextFactory<TvContext> _dbContextFactory;
    private readonly ChannelWriter<IBackgroundServiceRequest> _workerChannel;

    public UpdateExternalJsonPlayoutHandler(
        IDbContextFactory<TvContext> dbContextFactory,
        ChannelWriter<IBackgroundServiceRequest> workerChannel)
    {
        _dbContextFactory = dbContextFactory;
        _workerChannel = workerChannel;
    }

    public async Task<Either<BaseError, PlayoutNameViewModel>> Handle(
        UpdateExternalJsonPlayout request,
        CancellationToken cancellationToken)
    {
        await using TvContext dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
        Validation<BaseError, Playout> validation = await Validate(dbContext, request, cancellationToken);
        return await validation.Apply(playout => ApplyUpdateRequest(dbContext, request, playout, cancellationToken));
    }

    private async Task<PlayoutNameViewModel> ApplyUpdateRequest(
        TvContext dbContext,
        UpdateExternalJsonPlayout request,
        Playout playout,
        CancellationToken cancellationToken)
    {
        playout.ScheduleFile = request.ScheduleFile;

        // Rotate the playout ETag only when the schedule-file actually changed — a no-op re-submit must
        // not bump (#269). When it changed, force-write past a concurrent Version bump from a replace-all
        // editor (this writer takes no If-Match, so a benign race must not 500) — #253/#269 §7a.
        if (dbContext.ChangeTracker.HasChanges())
        {
            playout.Version++;
            await dbContext.SaveChangesForcingVersion(cancellationToken);

            // post-commit side effect runs on CancellationToken.None so a late request cancellation
            // can't abort it after the commit landed (#254)
            await _workerChannel.WriteAsync(new RefreshChannelData(playout.Channel.Number), CancellationToken.None);
        }

        return new PlayoutNameViewModel(
            playout.Id,
            playout.ScheduleKind,
            playout.Channel.Name,
            playout.Channel.Number,
            playout.Channel.Id,
            playout.Channel.PlayoutMode,
            playout.ProgramSchedule?.Name ?? string.Empty,
            playout.ScheduleFile,
            playout.DailyRebuildTime,
            playout.BuildStatus,
            playout.DecoId,
            playout.Deco?.Name,
            playout.Version,
            playout.Seed);
    }

    private static Task<Validation<BaseError, Playout>> Validate(
        TvContext dbContext,
        UpdateExternalJsonPlayout request,
        CancellationToken cancellationToken) =>
        PlayoutMustExist(dbContext, request, cancellationToken);

    private static Task<Validation<BaseError, Playout>> PlayoutMustExist(
        TvContext dbContext,
        UpdateExternalJsonPlayout updatePlayout,
        CancellationToken cancellationToken) =>
        dbContext.Playouts
            .Include(p => p.Channel)
            .SelectOneAsync(p => p.Id, p => p.Id == updatePlayout.PlayoutId, cancellationToken)
            .Map(o => o.ToValidation<BaseError>("Playout does not exist."));
}
