using System.Globalization;
using System.Text.RegularExpressions;
using System.Threading.Channels;
using ErsatzTV.Core;
using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Domain.Filler;
using ErsatzTV.Core.Interfaces.Images;
using ErsatzTV.Core.Interfaces.Search;
using ErsatzTV.Infrastructure.Data;
using ErsatzTV.Infrastructure.Extensions;
using Microsoft.EntityFrameworkCore;
using static ErsatzTV.Application.Channels.ChannelValidations;
using Channel = ErsatzTV.Core.Domain.Channel;

namespace ErsatzTV.Application.Channels;

public class CreateChannelHandler(
    ChannelWriter<IBackgroundServiceRequest> workerChannel,
    IDbContextFactory<TvContext> dbContextFactory,
    ISearchTargets searchTargets,
    IRemoteLogoCacher remoteLogoCacher)
    : IRequestHandler<CreateChannel, Either<BaseError, CreateChannelResult>>
{
    public async Task<Either<BaseError, CreateChannelResult>> Handle(
        CreateChannel request,
        CancellationToken cancellationToken)
    {
        await using TvContext dbContext = await dbContextFactory.CreateDbContextAsync(cancellationToken);
        Validation<BaseError, Channel> validation = await Validate(dbContext, request, cancellationToken);
        return await validation.Match(
            Succ: async channel =>
            {
                Either<BaseError, string> resolvedLogo = await ResolveLogoPath(request, cancellationToken);
                return await resolvedLogo.Match(
                    Right: async logoPath =>
                    {
                        ApplyResolvedLogo(request, channel, logoPath);
                        return Right<BaseError, CreateChannelResult>(await PersistChannel(dbContext, channel));
                    },
                    Left: e => Task.FromResult(Left<BaseError, CreateChannelResult>(e)));
            },
            Fail: errors => Task.FromResult(Left<BaseError, CreateChannelResult>(errors.Join())));
    }

    // Resolve the incoming logo path into a value safe to persist. An external http(s) URL is
    // downloaded and cached (a cacher Left fails the whole save); an empty path or an
    // already-local/cached path passes through unchanged. (ersatztv#525)
    private async Task<Either<BaseError, string>> ResolveLogoPath(
        CreateChannel request,
        CancellationToken cancellationToken)
    {
        string path = request.Logo?.Path ?? string.Empty;

        if (!Artwork.IsExternalUrl(path))
        {
            return path;
        }

        Either<BaseError, string> cached = await remoteLogoCacher.CacheFromUrl(new Uri(path), cancellationToken);
        return cached;
    }

    // When the incoming logo was an external URL, swap the downloaded cache name onto the logo
    // artwork built during validation so no URL is ever persisted in Artwork.Path. (ersatztv#525)
    private static void ApplyResolvedLogo(CreateChannel request, Channel channel, string resolvedLogoPath)
    {
        if (!Artwork.IsExternalUrl(request.Logo?.Path ?? string.Empty))
        {
            return;
        }

        foreach (Artwork logo in channel.Artwork.Where(a => a.ArtworkKind == ArtworkKind.Logo))
        {
            logo.Path = resolvedLogoPath;
        }
    }

    private async Task<CreateChannelResult> PersistChannel(TvContext dbContext, Channel channel)
    {
        await dbContext.Channels.AddAsync(channel);
        await dbContext.SaveChangesAsync();
        searchTargets.SearchTargetsChanged();
        await workerChannel.WriteAsync(new RefreshChannelList());
        return new CreateChannelResult(channel.Id);
    }

    private static async Task<Validation<BaseError, Channel>> Validate(TvContext dbContext, CreateChannel request, CancellationToken cancellationToken)
    {
        Validation<BaseError, Channel> channelValidation = (ValidateName(request), await ValidateNumber(dbContext, request, cancellationToken),
            await FFmpegProfileMustExist(dbContext, request, cancellationToken),
            await WatermarkMustExist(dbContext, request, cancellationToken),
            await FillerPresetMustExist(dbContext, request, cancellationToken),
            await MirrorSourceMustBeValid(dbContext, request, cancellationToken),
            ValidateShowInEpg(request.IsEnabled, request.ShowInEpg),
            ValidateLogo(request.Logo?.Path))
        .Apply((
            name,
            number,
            ffmpegProfileId,
            watermarkId,
            fillerPresetId,
            _,
            _,
            _) =>
        {
            var artwork = new List<Artwork>();
            if (!string.IsNullOrWhiteSpace(request.Logo?.Path))
            {
                string logo = request.Logo.Path;
                if (logo.StartsWith("iptv/logos/", StringComparison.Ordinal))
                {
                    logo = logo.Replace("iptv/logos/", string.Empty);
                }

                artwork.Add(
                    new Artwork
                    {
                        Path = logo,
                        ArtworkKind = ArtworkKind.Logo,
                        OriginalContentType = !string.IsNullOrEmpty(request.Logo.ContentType)
                            ? request.Logo.ContentType
                            : null,
                        DateAdded = DateTime.UtcNow,
                        DateUpdated = DateTime.UtcNow
                    });
            }

            var channel = new Channel(Guid.NewGuid())
            {
                Name = name,
                Number = number,
                SortNumber = double.Parse(number, CultureInfo.InvariantCulture),
                Group = request.Group,
                Categories = request.Categories,
                FFmpegProfileId = ffmpegProfileId,
                SlugSeconds = request.SlugSeconds,
                PlayoutSource = request.PlayoutSource,
                PlayoutMode = request.PlayoutMode,
                MirrorSourceChannelId = request.MirrorSourceChannelId,
                PlayoutOffset = request.PlayoutOffset,
                StreamingMode = request.StreamingMode,
                Artwork = artwork,
                StreamSelectorMode = request.StreamSelectorMode,
                StreamSelector = request.StreamSelector,
                PreferredAudioLanguageCode = request.PreferredAudioLanguageCode,
                PreferredAudioTitle = request.PreferredAudioTitle,
                PreferredSubtitleLanguageCode = request.PreferredSubtitleLanguageCode,
                SubtitleMode = request.SubtitleMode,
                MusicVideoCreditsMode = request.MusicVideoCreditsMode,
                MusicVideoCreditsTemplate = request.MusicVideoCreditsTemplate,
                SongVideoMode = request.SongVideoMode,
                TranscodeMode = request.TranscodeMode,
                IdleBehavior = request.IdleBehavior,
                IsEnabled = request.IsEnabled,
                ShowInEpg = request.IsEnabled && request.ShowInEpg,
                Origin = ChannelOrigin.UserCreated
            };

            if (channel.PlayoutSource is ChannelPlayoutSource.Mirror)
            {
                channel.PlayoutMode = ChannelPlayoutMode.Continuous;
            }
            else
            {
                channel.MirrorSourceChannelId = null;
                channel.PlayoutOffset = null;
            }

            foreach (int id in watermarkId)
            {
                channel.WatermarkId = id;
            }

            foreach (int id in fillerPresetId)
            {
                channel.FallbackFillerId = id;
            }

            return channel;
        });

        // combine the page-only Group rule with the channel validation (keeps tuple arity within
        // LanguageExt's supported applicative range while still accumulating all errors)
        return (ValidateGroup(request.Group), channelValidation).Apply((_, channel) => channel);
    }

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

    private static async Task<Validation<BaseError, string>> ValidateNumber(
        TvContext dbContext,
        CreateChannel createChannel,
        CancellationToken cancellationToken)
    {
        Option<Channel> maybeExistingChannel = await dbContext.Channels
            .SelectOneAsync(c => c.Number, c => c.Number == createChannel.Number, cancellationToken);
        return maybeExistingChannel.Match<Validation<BaseError, string>>(
            _ => BaseError.New("Channel number must be unique"),
            () =>
            {
                if (Regex.IsMatch(createChannel.Number, Channel.NumberValidator))
                {
                    return createChannel.Number;
                }

                return BaseError.New("Invalid channel number; two decimals are allowed for subchannels");
            });
    }

    private static async Task<Validation<BaseError, int>> FFmpegProfileMustExist(
        TvContext dbContext,
        CreateChannel createChannel,
        CancellationToken cancellationToken)
    {
        bool exists = await dbContext.FFmpegProfiles
            .AnyAsync(p => p.Id == createChannel.FFmpegProfileId, cancellationToken);
        if (exists)
        {
            return createChannel.FFmpegProfileId;
        }

        return BaseError.New($"FFmpegProfile {createChannel.FFmpegProfileId} does not exist.");
    }

    private static async Task<Validation<BaseError, Option<int>>> WatermarkMustExist(
        TvContext dbContext,
        CreateChannel createChannel,
        CancellationToken cancellationToken)
    {
        if (createChannel.WatermarkId is null)
        {
            return Option<int>.None;
        }

        bool exists = await dbContext.ChannelWatermarks
            .AnyAsync(w => w.Id == createChannel.WatermarkId, cancellationToken);
        if (exists)
        {
            return Optional(createChannel.WatermarkId);
        }

        return BaseError.New($"Watermark {createChannel.WatermarkId} does not exist.");
    }

    private static async Task<Validation<BaseError, Option<int>>> FillerPresetMustExist(
        TvContext dbContext,
        CreateChannel createChannel,
        CancellationToken cancellationToken)
    {
        if (createChannel.FallbackFillerId is null)
        {
            return Option<int>.None;
        }

        bool exists = await dbContext.FillerPresets
            .Filter(fp => fp.FillerKind == FillerKind.Fallback)
            .AnyAsync(w => w.Id == createChannel.FallbackFillerId, cancellationToken);
        if (exists)
        {
            return Optional(createChannel.FallbackFillerId);
        }

        return BaseError.New($"Fallback filler {createChannel.FallbackFillerId} does not exist.");
    }

    private static async Task<Validation<BaseError, Unit>> MirrorSourceMustBeValid(
        TvContext dbContext,
        CreateChannel createChannel,
        CancellationToken cancellationToken)
    {
        if (createChannel.PlayoutSource is not ChannelPlayoutSource.Mirror)
        {
            return Unit.Default;
        }

        Option<Channel> maybeMirrorSource = await dbContext.Channels
            .AsNoTracking()
            .SelectOneAsync(
                c => c.Id == createChannel.MirrorSourceChannelId,
                c => c.Id == createChannel.MirrorSourceChannelId,
                cancellationToken);

        if (maybeMirrorSource.IsNone)
        {
            return BaseError.New("Mirror source channel does not exist.");
        }

        foreach (var mirrorSource in maybeMirrorSource)
        {
            if (mirrorSource.PlayoutSource is not ChannelPlayoutSource.Generated)
            {
                return BaseError.New(
                    $"Mirror source channel {mirrorSource.Name} must use generated playout source");
            }
        }

        foreach (TimeSpan playoutOffset in Optional(createChannel.PlayoutOffset))
        {
            if (playoutOffset < TimeSpan.FromHours(-12) || playoutOffset > TimeSpan.FromHours(12))
            {
                return BaseError.New("Playout offset must not be greater than 12 hours");
            }
        }

        return Unit.Default;
    }
}
