using System.Threading.Channels;
using ErsatzTV.Application.Playouts;
using ErsatzTV.Core;
using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Errors;
using ErsatzTV.Core.Scheduling;
using ErsatzTV.Infrastructure.Data;
using Microsoft.EntityFrameworkCore;
using static ErsatzTV.Application.ProgramSchedules.Mapper;

namespace ErsatzTV.Application.ProgramSchedules;

public class AddProgramScheduleItemHandler : ProgramScheduleItemCommandBase,
    IRequestHandler<AddProgramScheduleItem, Either<BaseError, ProgramScheduleItemViewModel>>
{
    private readonly ChannelWriter<IBackgroundServiceRequest> _channel;
    private readonly IDbContextFactory<TvContext> _dbContextFactory;

    public AddProgramScheduleItemHandler(
        IDbContextFactory<TvContext> dbContextFactory,
        ChannelWriter<IBackgroundServiceRequest> channel)
    {
        _dbContextFactory = dbContextFactory;
        _channel = channel;
    }

    public async Task<Either<BaseError, ProgramScheduleItemViewModel>> Handle(
        AddProgramScheduleItem request,
        CancellationToken cancellationToken)
    {
        await using TvContext dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
        Option<ProgramSchedule> maybeProgramSchedule =
            await ProgramScheduleMustExist(dbContext, request.ProgramScheduleId, cancellationToken);
        return await maybeProgramSchedule.Match(
            Some: async programSchedule =>
            {
                Validation<BaseError, ProgramSchedule> validation = await Validate(dbContext, request, programSchedule);
                return await validation.Apply(ps => PersistItem(dbContext, request, ps, cancellationToken));
            },
            None: () => Task.FromResult<Either<BaseError, ProgramScheduleItemViewModel>>(
                new NotFoundError("[ProgramScheduleId] does not exist.")));
    }

    private async Task<ProgramScheduleItemViewModel> PersistItem(
        TvContext dbContext,
        AddProgramScheduleItem request,
        ProgramSchedule programSchedule,
        CancellationToken cancellationToken)
    {
        int nextIndex = programSchedule.Items.Select(i => i.Index).DefaultIfEmpty(0).Max() + 1;

        ProgramScheduleItem item = BuildItem(programSchedule, nextIndex, request);
        programSchedule.Items.Add(item);

        // bump the optimistic-concurrency token so this config edit rotates other clients' ETags (#253)
        programSchedule.Version++;

        await dbContext.SaveChangesAsync(cancellationToken);

        // refresh any playouts that use this schedule
        // post-commit side effect runs on CancellationToken.None so a late request cancellation
        // can't abort it after the commit landed (#254)
        foreach (Playout playout in programSchedule.Playouts)
        {
            await _channel.WriteAsync(new BuildPlayout(playout.Id, PlayoutBuildMode.Refresh), CancellationToken.None);
        }

        // reload with the full navigation graph before projecting: BuildItem creates the watermark/graphics
        // join rows with only their foreign-key ids set, so the tracked entities have null Watermark /
        // GraphicsElement navs that ProjectToViewModel dereferences (would 500 on POST — see #229).
        ProgramScheduleItem persisted = await dbContext.ProgramScheduleItems
            .Filter(psi => psi.Id == item.Id)
            .IncludeScheduleItemDetails()
            .SingleAsync(cancellationToken);

        return ProjectToViewModel(persisted);
    }

    private static async Task<Validation<BaseError, ProgramSchedule>> Validate(
        TvContext dbContext,
        AddProgramScheduleItem request,
        ProgramSchedule programSchedule)
    {
        Validation<BaseError, ProgramSchedule> validation =
            PlayoutModeMustBeValid(request, programSchedule)
                .Bind(programSchedule => CollectionTypeMustBeValid(request, programSchedule));

        return await validation.ToEither().Match(
            Left: error => Task.FromResult<Validation<BaseError, ProgramSchedule>>(
                Fail<BaseError, ProgramSchedule>(error)),
            Right: async validProgramSchedule =>
            {
                Either<BaseError, ProgramSchedule> fillerResult = await FillerConfigurationMustBeValid(
                    dbContext,
                    request,
                    validProgramSchedule);
                return fillerResult.ToValidation();
            });
    }
}