using System.Globalization;
using System.IO.Abstractions;
using System.Runtime.InteropServices;
using System.Threading.Channels;
using ErsatzTV.Application.Channels;
using ErsatzTV.Application.FFmpegProfiles;
using ErsatzTV.Application.Graphics;
using ErsatzTV.Application.Maintenance;
using ErsatzTV.Core;
using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Errors;
using ErsatzTV.Core.FFmpeg;
using ErsatzTV.Core.Interfaces.FFmpeg;
using ErsatzTV.Core.Interfaces.Metadata;
using ErsatzTV.Core.Interfaces.Repositories;
using ErsatzTV.Core.Next.Config;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Subtitle = ErsatzTV.Core.Next.Config.Subtitle;

namespace ErsatzTV.Application.Streaming;

public class StartFFmpegNextSessionHandler(
    IServiceScopeFactory serviceScopeFactory,
    IFileSystem fileSystem,
    ILocalFileSystem localFileSystem,
    IFFmpegSegmenterService ffmpegSegmenterService,
    IConfigElementRepository configElementRepository,
    IHostApplicationLifetime hostApplicationLifetime,
    IMediator mediator,
    ChannelWriter<IBackgroundServiceRequest> workerChannel,
    ILogger<StartFFmpegNextSessionHandler> logger,
    ILogger<NextSessionWorker> sessionWorkerLogger)
    : IRequestHandler<StartFFmpegNextSession, Either<BaseError, string>>
{
    public Task<Either<BaseError, string>> Handle(
        StartFFmpegNextSession request,
        CancellationToken cancellationToken) =>
        Validate(request, cancellationToken)
            .MapT(validationResult => StartProcess(request, validationResult, cancellationToken))
            // this weirdness is needed to maintain the error type (.ToEitherAsync() just gives BaseError)
#pragma warning disable VSTHRD103
            .Bind(v => v.ToEither().MapLeft(seq => seq.Head()).MapAsync<BaseError, Task<string>, string>(identity));
#pragma warning restore VSTHRD103

    private async Task<string> StartProcess(
        StartFFmpegNextSession request,
        ValidationResult validationResult,
        CancellationToken cancellationToken)
    {
        Option<TimeSpan> idleTimeout = Option<TimeSpan>.None;

        // Option<FrameRate> targetFramerate = await mediator.Send(
        //     new GetChannelFramerate(request.ChannelNumber),
        //     cancellationToken);

        // only load timeout when needed
        if (validationResult.Channel.IdleBehavior is not ChannelIdleBehavior.KeepRunning)
        {
            idleTimeout = await configElementRepository
                .GetValue<int>(ConfigElementKey.FFmpegSegmenterTimeout, cancellationToken)
                .Map(maybeTimeout => maybeTimeout.Match(i => TimeSpan.FromSeconds(i), () => TimeSpan.FromMinutes(1)));
        }

        await mediator.Send(new RefreshGraphicsElements(), cancellationToken);

        ChannelConfig config = await MapConfig(
            validationResult.Channel,
            validationResult.FfmpegProfile,
            cancellationToken);

        NextSessionWorker worker = new NextSessionWorker(
            validationResult.ChannelBinary,
            config,
            fileSystem,
            localFileSystem,
            serviceScopeFactory,
            sessionWorkerLogger);

        ffmpegSegmenterService.AddOrUpdateWorker(request.ChannelNumber, worker);

        // fire and forget worker
        _ = worker.Run(request.ChannelNumber, idleTimeout, hostApplicationLifetime.ApplicationStopping)
            .ContinueWith(
                _ =>
                {
                    ffmpegSegmenterService.RemoveWorker(request.ChannelNumber, out IHlsSessionWorker inactiveWorker);

                    inactiveWorker?.Dispose();

                    workerChannel.TryWrite(new ReleaseMemory(false));
                },
                TaskScheduler.Default);

        int initialSegmentCount = await configElementRepository
            .GetValue<int>(ConfigElementKey.FFmpegInitialSegmentCount, cancellationToken)
            .Map(maybeCount => maybeCount.Match(identity, () => 1));

        await worker.WaitForPlaylistSegments(initialSegmentCount, cancellationToken);

        return await GetMultiVariantPlaylist(request);
    }

    private Task<Validation<BaseError, ValidationResult>> Validate(
        StartFFmpegNextSession request,
        CancellationToken cancellationToken) =>
        SessionMustBeInactive(request)
            .BindT(_ => FolderMustBeEmpty(request))
            .BindT(_ => ChannelBinaryMustExist())
            .BindT(result => ChannelMustExist(request, result, cancellationToken))
            .BindT(result => FFmpegProfileMustExist(result, cancellationToken));

    private async Task<Validation<BaseError, Unit>> SessionMustBeInactive(StartFFmpegNextSession request)
    {
        var result = Optional(ffmpegSegmenterService.TryAddWorker(request.ChannelNumber, null))
            .Where(success => success)
            .Map(_ => Unit.Default)
            .ToValidation<BaseError>(new ChannelSessionAlreadyActive(await GetMultiVariantPlaylist(request)));

        if (result.IsFail && ffmpegSegmenterService.TryGetWorker(
                request.ChannelNumber,
                out IHlsSessionWorker worker))
        {
            worker?.Touch(Option<string>.None);
        }

        return result;
    }

    private Task<Validation<BaseError, Unit>> FolderMustBeEmpty(StartFFmpegNextSession request)
    {
        string folder = Path.Combine(FileSystemLayout.TranscodeFolder, request.ChannelNumber);
        logger.LogDebug("Preparing transcode folder {Folder}", folder);

        localFileSystem.EnsureFolderExists(folder);
        localFileSystem.EmptyFolder(folder);

        return Task.FromResult<Validation<BaseError, Unit>>(Unit.Default);
    }

    private Task<Validation<BaseError, ValidationResult>> ChannelBinaryMustExist()
    {
        string nextFolder = SystemEnvironment.NextFolder;
        if (string.IsNullOrWhiteSpace(nextFolder))
        {
            string processFileName = Environment.ProcessPath ?? string.Empty;
            string processExecutable = Path.GetFileNameWithoutExtension(processFileName);
            nextFolder = Path.GetDirectoryName(processFileName);
            if ("dotnet".Equals(processExecutable, StringComparison.OrdinalIgnoreCase))
            {
                nextFolder = AppContext.BaseDirectory;
            }
        }

        string executable = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
            ? "ersatztv-channel.exe"
            : "ersatztv-channel";

        string channelBinary = fileSystem.Path.Combine(ReplaceTilde(nextFolder), executable);
        if (!fileSystem.Path.Exists(channelBinary))
        {
            return Task.FromResult<Validation<BaseError, ValidationResult>>(
                BaseError.New("ersatztv-channel binary does not exist!"));
        }

        return Task.FromResult<Validation<BaseError, ValidationResult>>(
            new ValidationResult(channelBinary, null, null));
    }

    private async Task<Validation<BaseError, ValidationResult>> ChannelMustExist(
        StartFFmpegNextSession request,
        ValidationResult result,
        CancellationToken cancellationToken)
    {
        Option<ChannelViewModel> maybeChannel = await mediator.Send(
            new GetChannelByNumber(request.ChannelNumber),
            cancellationToken);

        foreach (ChannelViewModel channel in maybeChannel)
        {
            return result with { Channel = channel };
        }

        return BaseError.New($"Channel number {request.ChannelNumber} does not exist");
    }

    private async Task<Validation<BaseError, ValidationResult>> FFmpegProfileMustExist(
        ValidationResult result,
        CancellationToken cancellationToken)
    {
        Option<FFmpegProfileViewModel> maybeFFmpegProfile = await mediator.Send(
            new GetFFmpegProfileById(result.Channel.FFmpegProfileId),
            cancellationToken);

        foreach (FFmpegProfileViewModel ffmpegProfile in maybeFFmpegProfile)
        {
            return result with { FfmpegProfile = ffmpegProfile };
        }

        return BaseError.New($"FFmpeg profile {result.Channel.FFmpegProfileId} not exist");
    }

    public string ReplaceTilde(string path)
    {
        if (!path.StartsWith('~'))
        {
            return path;
        }

        string userFolder = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);

        switch (path)
        {
            case "~":
                return userFolder;
            case not null
                when path.Length == 2 &&
                     (path[1] == fileSystem.Path.DirectorySeparatorChar ||
                      path[1] == fileSystem.Path.AltDirectorySeparatorChar):
                return userFolder + fileSystem.Path.DirectorySeparatorChar;
            default:
                return fileSystem.Path.Combine(userFolder, path[2..]);
        }
    }

    private async Task<string> GetMultiVariantPlaylist(StartFFmpegNextSession request)
    {
        var variantPlaylist =
            $"{request.Scheme}://{request.Host}{request.PathBase}/iptv/session/{request.ChannelNumber}/live.m3u8{request.AccessTokenQuery}";

        var subtitlePlaylist =
            $"{request.Scheme}://{request.Host}{request.PathBase}/iptv/session/{request.ChannelNumber}/live_sub.m3u8{request.AccessTokenQuery}";

        Option<ChannelStreamingSpecsViewModel> maybeStreamingSpecs =
            await mediator.Send(new GetChannelStreamingSpecs(request.ChannelNumber));
        string resolution = string.Empty;
        var bitrate = "10000000";
        foreach (ChannelStreamingSpecsViewModel streamingSpecs in maybeStreamingSpecs)
        {
            string videoCodec = streamingSpecs.VideoFormat switch
            {
                FFmpegProfileVideoFormat.Av1 => "av01.0.01M.08",
                FFmpegProfileVideoFormat.Hevc => "hvc1.1.6.L93.B0",
                FFmpegProfileVideoFormat.H264 => "avc1.4D4028",
                _ => string.Empty
            };

            string audioCodec = streamingSpecs.AudioFormat switch
            {
                FFmpegProfileAudioFormat.Ac3 => "ac-3",
                FFmpegProfileAudioFormat.Aac or FFmpegProfileAudioFormat.AacLatm => "mp4a.40.2",
                _ => string.Empty
            };

            List<string> codecStrings = [];
            if (!string.IsNullOrWhiteSpace(videoCodec))
            {
                codecStrings.Add(videoCodec);
            }

            if (!string.IsNullOrWhiteSpace(audioCodec))
            {
                codecStrings.Add(audioCodec);
            }

            string codecs = codecStrings.Count > 0 ? $",CODECS=\"{string.Join(",", codecStrings)}\"" : string.Empty;
            resolution = $",RESOLUTION={streamingSpecs.Width}x{streamingSpecs.Height}{codecs}";
            bitrate = streamingSpecs.Bitrate.ToString(CultureInfo.InvariantCulture);
        }

        return $@"#EXTM3U
#EXT-X-VERSION:6
#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID=""subs"",NAME=""English"",DEFAULT=YES,AUTOSELECT=YES,FORCED=NO,LANGUAGE=""en"",URI=""{subtitlePlaylist}""
#EXT-X-STREAM-INF:BANDWIDTH={bitrate}{resolution}
{variantPlaylist}";
    }

    private async Task<ChannelConfig> MapConfig(
        ChannelViewModel channel,
        FFmpegProfileViewModel ffmpegProfile,
        CancellationToken cancellationToken)
    {
        var ffmpeg = new Ffmpeg
        {
            // next only keeps errors, so always pass the folder
            ReportsFolder = FileSystemLayout.FFmpegReportsFolder
        };

        Option<string> ffmpegPath = await configElementRepository.GetValue<string>(
            ConfigElementKey.FFmpegPath,
            cancellationToken);

        foreach (string path in ffmpegPath)
        {
            ffmpeg.FfmpegPath = path;
        }

        Option<string> ffprobePath = await configElementRepository.GetValue<string>(
            ConfigElementKey.FFprobePath,
            cancellationToken);

        foreach (string path in ffprobePath)
        {
            ffmpeg.FfprobePath = path;
        }

        Option<bool> maybeSaveReports = await configElementRepository.GetValue<bool>(
            ConfigElementKey.FFmpegSaveReports,
            cancellationToken);

        var audioNormalization = new Audio
        {
            Format = ffmpegProfile.AudioFormat switch
            {
                FFmpegProfileAudioFormat.Ac3 => AudioFormat.Ac3,
                _ => AudioFormat.Aac
            },
            BitrateKbps = ffmpegProfile.AudioBitrate,
            BufferKbps = ffmpegProfile.AudioBufferSize,
            Channels = ffmpegProfile.AudioChannels,
            SampleRateHz = ffmpegProfile.AudioSampleRate * 1000
        };

        if (ffmpegProfile.NormalizeLoudnessMode is NormalizeLoudnessMode.LoudNorm)
        {
            audioNormalization.NormalizeLoudness = true;
            audioNormalization.Loudness = new LoudnessClass
            {
                IntegratedTarget = ffmpegProfile.TargetLoudness
            };
        }

        string tonemapAlgorithm = ffmpegProfile.TonemapAlgorithm switch
        {
            FFmpegProfileTonemapAlgorithm.Clip => "clip",
            FFmpegProfileTonemapAlgorithm.Gamma => "gamma",
            FFmpegProfileTonemapAlgorithm.Reinhard => "reinhard",
            FFmpegProfileTonemapAlgorithm.Mobius => "mobius",
            FFmpegProfileTonemapAlgorithm.Hable => "hable",
            _ => "linear"
        };

        var videoNormalization = new Video
        {
            Format = ffmpegProfile.VideoFormat switch
            {
                FFmpegProfileVideoFormat.Hevc => VideoFormat.Hevc,
                _ => VideoFormat.H264
            },
            BitDepth = ffmpegProfile.BitDepth switch
            {
                FFmpegProfileBitDepth.TenBit => 10,
                _ => 8
            },
            Accel = ffmpegProfile.HardwareAcceleration switch
            {
                HardwareAccelerationKind.Amf => AccelEnum.Amf,
                HardwareAccelerationKind.Nvenc => AccelEnum.Cuda,
                HardwareAccelerationKind.Qsv => AccelEnum.Qsv,
                HardwareAccelerationKind.Rkmpp => AccelEnum.Rkmpp,
                HardwareAccelerationKind.Vaapi => AccelEnum.Vaapi,
                HardwareAccelerationKind.VideoToolbox => AccelEnum.Videotoolbox,
                _ => null
            },
            Height = ffmpegProfile.Resolution.Height,
            Width = ffmpegProfile.Resolution.Width,
            BitrateKbps = ffmpegProfile.VideoBitrate,
            BufferKbps = ffmpegProfile.VideoBufferSize,
            ScalingMode = ffmpegProfile.ScalingBehavior switch
            {
                ScalingBehavior.Stretch => ScalingMode.Stretch,
                ScalingBehavior.Crop => ScalingMode.Crop,
                _ => ScalingMode.ScaleAndPad
            },
            Deinterlace = ffmpegProfile.DeinterlaceVideo,
            Filters = new Filters
            {
                Tonemap = new TonemapClass
                {
                    Tonemap = tonemapAlgorithm
                },
                TonemapOpencl = new TonemapOpenclClass
                {
                    Tonemap = tonemapAlgorithm
                },
                Libplacebo = new LibplaceboClass
                {
                    Tonemapping = tonemapAlgorithm
                }
            },
            VaapiDevice = ffmpegProfile.VaapiDevice,
            VaapiDriver = ffmpegProfile.VaapiDriver switch
            {
                VaapiDriver.i965 => VaapiDriverEnum.I965,
                VaapiDriver.RadeonSI => VaapiDriverEnum.Radeonsi,
                _ => VaapiDriverEnum.Ihd
            }
        };

        var subtitleNormalization = new Subtitle
        {
            Mode = channel.NextEngineTextSubtitleMode switch
            {
                NextEngineTextSubtitleMode.Convert => Mode.Convert,
                _ => Mode.Burn
            }
        };

        string playoutFolder = fileSystem.Path.Combine(FileSystemLayout.NextPlayoutsFolder, channel.Number, "current");

        return new ChannelConfig
        {
            Playout = new Core.Next.Config.Playout
            {
                Folder = playoutFolder
            },
            Ffmpeg = ffmpeg,
            Normalization = new Normalization
            {
                Audio = audioNormalization,
                Video = videoNormalization,
                Subtitle = subtitleNormalization
            }
        };
    }

    private sealed record ValidationResult(
        string ChannelBinary,
        ChannelViewModel Channel,
        FFmpegProfileViewModel FfmpegProfile);
}