using System.Threading;
using System.Threading.Channels;
using System.Threading.Tasks;
using ErsatzTV.Application.Playouts.Commands;
using ErsatzTV.Core;
using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Interfaces.Repositories;
using ErsatzTV.Infrastructure.Data;
using ErsatzTV.Infrastructure.Extensions;
using LanguageExt;
using Microsoft.EntityFrameworkCore;

namespace ErsatzTV.Application.MediaCollections.Commands
{
    public class UpdateCollectionHandler : MediatR.IRequestHandler<UpdateCollection, Either<BaseError, Unit>>
    {
        private readonly ChannelWriter<IBackgroundServiceRequest> _channel;
        private readonly IDbContextFactory<TvContext> _dbContextFactory;
        private readonly IMediaCollectionRepository _mediaCollectionRepository;

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

        public async Task<Either<BaseError, Unit>> Handle(
            UpdateCollection request,
            CancellationToken cancellationToken)
        {
            await using TvContext dbContext = _dbContextFactory.CreateDbContext();
            Validation<BaseError, Collection> validation = await Validate(dbContext, request);
            return await validation.Apply(c => ApplyUpdateRequest(dbContext, c, request));
        }

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

            if (await dbContext.SaveChangesAsync() > 0 && request.UseCustomPlaybackOrder.IsSome)
            {
                // rebuild all playouts that use this collection
                foreach (int playoutId in await _mediaCollectionRepository.PlayoutIdsUsingCollection(
                    request.CollectionId))
                {
                    await _channel.WriteAsync(new BuildPlayout(playoutId, true));
                }
            }

            return Unit.Default;
        }

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

        private static Task<Validation<BaseError, Collection>> CollectionMustExist(
            TvContext dbContext,
            UpdateCollection updateCollection) =>
            dbContext.Collections
                .SelectOneAsync(c => c.Id, c => c.Id == updateCollection.CollectionId)
                .Map(o => o.ToValidation<BaseError>("Collection does not exist."));

        private static Validation<BaseError, string> ValidateName(UpdateCollection updateSimpleMediaCollection) =>
            updateSimpleMediaCollection.NotEmpty(c => c.Name)
                .Bind(_ => updateSimpleMediaCollection.NotLongerThan(50)(c => c.Name));
    }
}