using System.Globalization;
using System.Text.RegularExpressions;
using System.Threading.Channels;
using ErsatzTV.Core;
using ErsatzTV.Core.Errors;
using ErsatzTV.Infrastructure.Data;
using Microsoft.EntityFrameworkCore;
using Channel = ErsatzTV.Core.Domain.Channel;

namespace ErsatzTV.Application.Channels;

public class UpdateChannelNumbersHandler(
    IDbContextFactory<TvContext> dbContextFactory,
    ChannelWriter<IBackgroundServiceRequest> workerChannel)
    : IRequestHandler<UpdateChannelNumbers, Option<BaseError>>
{
    public async Task<Option<BaseError>> Handle(UpdateChannelNumbers request, CancellationToken cancellationToken)
    {
        Option<BaseError> validationError = ValidateRequest(request);
        if (validationError.IsSome)
        {
            return validationError;
        }

        await using TvContext dbContext = await dbContextFactory.CreateDbContextAsync(cancellationToken);
        await using var transaction = await dbContext.Database.BeginTransactionAsync(cancellationToken);

        try
        {
            var numberUpdates = request.Channels.ToDictionary(c => c.Id, c => c.Number);
            List<int> channelIds = numberUpdates.Keys.ToList();

            List<Channel> channelsToUpdate = await dbContext.Channels
                .Where(c => channelIds.Contains(c.Id))
                .ToListAsync(cancellationToken);

            if (channelsToUpdate.Count != channelIds.Count)
            {
                var found = channelsToUpdate.Select(c => c.Id).ToHashSet();
                int missingId = channelIds.First(id => !found.Contains(id));
                return new NotFoundError($"Channel {missingId} does not exist.");
            }

            List<string> requestedNumbers = numberUpdates.Values.ToList();
            bool numberConflict = await dbContext.Channels
                .AnyAsync(
                    c => requestedNumbers.Contains(c.Number) && !channelIds.Contains(c.Id),
                    cancellationToken);
            if (numberConflict)
            {
                return BaseError.New("Channel number must be unique");
            }

            // give every channel a non-conflicting number
            foreach (var channel in channelsToUpdate)
            {
                channel.Number = $"-{channel.Id}";
            }

            // save those changes
            await dbContext.SaveChangesAsync(cancellationToken);

            // give every channel the proper new number
            foreach (var channel in channelsToUpdate)
            {
                channel.Number = numberUpdates[channel.Id];
                if (double.TryParse(channel.Number, CultureInfo.InvariantCulture, out double sortNumber))
                {
                    channel.SortNumber = sortNumber;
                }
                else
                {
                    return BaseError.New($"Failed to parse channel number {channel.Number}");
                }
            }

            // save those changes
            await dbContext.SaveChangesAsync(cancellationToken);

            // commit the transaction
            await transaction.CommitAsync(cancellationToken);

            // update channel list and xmltv
            await workerChannel.WriteAsync(new RefreshChannelList(), cancellationToken);
            foreach (var channel in channelsToUpdate)
            {
                await workerChannel.WriteAsync(new RefreshChannelData(channel.Number), cancellationToken);
            }

            return Option<BaseError>.None;
        }
        catch (Exception ex)
        {
            return BaseError.New("Failed to update channel numbers: " + ex.Message);
        }
    }

    private static Option<BaseError> ValidateRequest(UpdateChannelNumbers request)
    {
        if (request.Channels.Count == 0)
        {
            return BaseError.New("At least one channel is required");
        }

        if (request.Channels.Select(c => c.Id).Distinct().Count() != request.Channels.Count)
        {
            return BaseError.New("Channel ids must be unique");
        }

        if (request.Channels.Select(c => c.Number).Distinct(StringComparer.Ordinal).Count() != request.Channels.Count)
        {
            return BaseError.New("Channel number must be unique");
        }

        foreach (ChannelSortViewModel channel in request.Channels)
        {
            if (!Regex.IsMatch(channel.Number, Channel.NumberValidator))
            {
                return BaseError.New("Invalid channel number; two decimals are allowed for subchannels");
            }
        }

        return Option<BaseError>.None;
    }
}