using System.Collections.Generic;
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 LanguageExt;
using Microsoft.EntityFrameworkCore;
using static LanguageExt.Prelude;

namespace ErsatzTV.Application.Configuration.Commands
{
    public class
        UpdatePlayoutDaysToBuildHandler : MediatR.IRequestHandler<UpdatePlayoutDaysToBuild, Either<BaseError, Unit>>
    {
        private readonly IConfigElementRepository _configElementRepository;
        private readonly IDbContextFactory<TvContext> _dbContextFactory;
        private readonly ChannelWriter<IBackgroundServiceRequest> _workerChannel;

        public UpdatePlayoutDaysToBuildHandler(
            IConfigElementRepository configElementRepository,
            IDbContextFactory<TvContext> dbContextFactory,
            ChannelWriter<IBackgroundServiceRequest> workerChannel)
        {
            _configElementRepository = configElementRepository;
            _dbContextFactory = dbContextFactory;
            _workerChannel = workerChannel;
        }

        public async Task<Either<BaseError, Unit>> Handle(
            UpdatePlayoutDaysToBuild request,
            CancellationToken cancellationToken)
        {
            await using TvContext dbContext = _dbContextFactory.CreateDbContext();
            Validation<BaseError, Unit> validation = await Validate(request);
            return await validation.Apply<Unit, Unit>(_ => ApplyUpdate(dbContext, request.DaysToBuild));
        }

        private async Task<Unit> ApplyUpdate(TvContext dbContext, int daysToBuild)
        {
            await _configElementRepository.Upsert(ConfigElementKey.PlayoutDaysToBuild, daysToBuild);
            
            // build all playouts to proper number of days
            List<Playout> playouts = await dbContext.Playouts
                .Include(p => p.Channel)
                .ToListAsync();
            foreach (int playoutId in playouts.OrderBy(p => decimal.Parse(p.Channel.Number)).Map(p => p.Id))
            {
                await _workerChannel.WriteAsync(new BuildPlayout(playoutId));
            }
            
            return Unit.Default;
        }

        private static Task<Validation<BaseError, Unit>> Validate(UpdatePlayoutDaysToBuild request) =>
            Optional(request.DaysToBuild)
                .Where(days => days > 0)
                .Map(_ => Unit.Default)
                .ToValidation<BaseError>("Days to build must be greater than zero")
                .AsTask();
    }
}