using System.Linq;
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 UpdateCollectionCustomOrderHandler :
        MediatR.IRequestHandler<UpdateCollectionCustomOrder, Either<BaseError, Unit>>
    {
        private readonly ChannelWriter<IBackgroundServiceRequest> _channel;
        private readonly IDbContextFactory<TvContext> _dbContextFactory;
        private readonly IMediaCollectionRepository _mediaCollectionRepository;

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

        public async Task<Either<BaseError, Unit>> Handle(
            UpdateCollectionCustomOrder 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,
            UpdateCollectionCustomOrder request)
        {
            foreach (MediaItemCustomOrder updateItem in request.MediaItemCustomOrders)
            {
                Option<CollectionItem> maybeCollectionItem = c.CollectionItems
                    .FirstOrDefault(ci => ci.MediaItemId == updateItem.MediaItemId);

                foreach (CollectionItem collectionItem in maybeCollectionItem)
                {
                    collectionItem.CustomIndex = updateItem.CustomIndex;
                }
            }

            if (await dbContext.SaveChangesAsync() > 0)
            {
                // 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 Task<Validation<BaseError, Collection>> Validate(
            TvContext dbContext,
            UpdateCollectionCustomOrder request) =>
            CollectionMustExist(dbContext, request);

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