using System.Collections.Generic;
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.Infrastructure.Data;
using ErsatzTV.Infrastructure.Extensions;
using LanguageExt;
using MediatR;
using Microsoft.EntityFrameworkCore;

namespace ErsatzTV.Application.ProgramSchedules.Commands
{
    public class UpdateProgramScheduleHandler :
        IRequestHandler<UpdateProgramSchedule, Either<BaseError, UpdateProgramScheduleResult>>
    {
        private readonly ChannelWriter<IBackgroundServiceRequest> _channel;
        private readonly IDbContextFactory<TvContext> _dbContextFactory;

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

        public async Task<Either<BaseError, UpdateProgramScheduleResult>> Handle(
            UpdateProgramSchedule request,
            CancellationToken cancellationToken)
        {
            await using TvContext dbContext = _dbContextFactory.CreateDbContext();

            Validation<BaseError, ProgramSchedule> validation = await Validate(dbContext, request);
            return await validation.Apply(ps => ApplyUpdateRequest(dbContext, ps, request));
        }

        private async Task<UpdateProgramScheduleResult> ApplyUpdateRequest(
            TvContext dbContext,
            ProgramSchedule programSchedule,
            UpdateProgramSchedule request)
        {
            // we need to rebuild playouts if the playback order or keep multi-episodes has been modified
            bool needToRebuildPlayout =
                programSchedule.KeepMultiPartEpisodesTogether != request.KeepMultiPartEpisodesTogether ||
                programSchedule.TreatCollectionsAsShows != request.TreatCollectionsAsShows;

            programSchedule.Name = request.Name;
            programSchedule.KeepMultiPartEpisodesTogether = request.KeepMultiPartEpisodesTogether;
            programSchedule.TreatCollectionsAsShows = programSchedule.KeepMultiPartEpisodesTogether &&
                                                      request.TreatCollectionsAsShows;

            await dbContext.SaveChangesAsync();

            if (needToRebuildPlayout)
            {
                List<int> playoutIds = await dbContext.Playouts
                    .Filter(p => p.ProgramScheduleId == programSchedule.Id)
                    .Map(p => p.Id)
                    .ToListAsync();

                foreach (int playoutId in playoutIds)
                {
                    await _channel.WriteAsync(new BuildPlayout(playoutId, true));
                }
            }

            return new UpdateProgramScheduleResult(programSchedule.Id);
        }

        private static async Task<Validation<BaseError, ProgramSchedule>> Validate(
            TvContext dbContext,
            UpdateProgramSchedule request) =>
            (await ProgramScheduleMustExist(dbContext, request), ValidateName(request))
            .Apply((programSchedule, _) => programSchedule);

        private static Task<Validation<BaseError, ProgramSchedule>> ProgramScheduleMustExist(
            TvContext dbContext,
            UpdateProgramSchedule request) =>
            dbContext.ProgramSchedules
                .SelectOneAsync(ps => ps.Id, ps => ps.Id == request.ProgramScheduleId)
                .Map(o => o.ToValidation<BaseError>("ProgramSchedule does not exist"));

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