using System;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Sockets;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using YoutubeExplode;
using YoutubeExplode.Videos.Streams;

namespace Jellyfin.Plugin.CinemaTrailers4Jellyfins.Services
{
    public class TrailerDownloadService : IDisposable
    {
        private readonly ILogger<TrailerDownloadService> _logger;
        private readonly HttpClient _httpClient;

        public TrailerDownloadService(ILogger<TrailerDownloadService> logger)
        {
            _logger = logger;

            // Force IPv4 to avoid ~80s delay when IPv6 is unreachable (Happy Eyeballs fallback).
            var handler = new SocketsHttpHandler
            {
                ConnectCallback = async (ctx, ct) =>
                {
                    var entry = await Dns.GetHostEntryAsync(ctx.DnsEndPoint.Host, AddressFamily.InterNetwork, ct).ConfigureAwait(false);
                    var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                    socket.NoDelay = true;
                    try
                    {
                        await socket.ConnectAsync(entry.AddressList[0], ctx.DnsEndPoint.Port, ct).ConfigureAwait(false);
                        return new NetworkStream(socket, ownsSocket: true);
                    }
                    catch
                    {
                        socket.Dispose();
                        throw;
                    }
                }
            };
            _httpClient = new HttpClient(handler) { Timeout = TimeSpan.FromMinutes(10) };
        }

        public void Dispose() => _httpClient.Dispose();

        /// <summary>
        /// Downloads a YouTube video by key to outputPath.
        /// Uses yt-dlp when a valid path is configured (supports 1080p+, requires ffmpeg on PATH).
        /// Falls back to YoutubeExplode for built-in download (max 720p, no external tools needed).
        /// </summary>
        public async Task<bool> DownloadAsync(
            string youtubeKey,
            string outputPath,
            int preferredHeight,
            string ytDlpPath,
            CancellationToken ct)
        {
            Directory.CreateDirectory(Path.GetDirectoryName(outputPath)!);

            if (!string.IsNullOrWhiteSpace(ytDlpPath) && File.Exists(ytDlpPath))
            {
                if (await DownloadWithYtDlpAsync(youtubeKey, outputPath, preferredHeight, ytDlpPath, ct).ConfigureAwait(false))
                    return true;

                _logger.LogWarning("|CinemaTrailers4Jellyfins| yt-dlp failed for {Key}; falling back to the built-in downloader.", youtubeKey);
            }

            return await DownloadWithYoutubeExplodeAsync(youtubeKey, outputPath, preferredHeight, ct)
                .ConfigureAwait(false);
        }

        private async Task<bool> DownloadWithYoutubeExplodeAsync(
            string key,
            string outputPath,
            int preferredHeight,
            CancellationToken ct)
        {
            // Separate video/audio downloads land next to the output and are always removed,
            // whether the merge succeeds or not.
            var videoTemp = outputPath + ".video.tmp";
            var audioTemp = outputPath + ".audio.tmp";
            try
            {
                var youtube = new YoutubeClient(_httpClient);
                var manifest = await youtube.Videos.Streams
                    .GetManifestAsync($"https://www.youtube.com/watch?v={key}", ct)
                    .ConfigureAwait(false);

                // Muxed streams include audio+video in one file. YouTube rarely serves them
                // anymore, but use one when it exists since it needs no merge.
                var muxedStreams = manifest.GetMuxedStreams().ToList();
                if (muxedStreams.Count > 0)
                {
                    var muxed = PickByHeight(muxedStreams, preferredHeight);
                    _logger.LogInformation(
                        "|CinemaTrailers4Jellyfins| Downloading {Key} at {Quality} (muxed) to {Path}",
                        key, muxed.VideoQuality.Label, outputPath);
                    await youtube.Videos.Streams.DownloadAsync(muxed, outputPath, cancellationToken: ct).ConfigureAwait(false);
                    return true;
                }

                // Otherwise download the best video-only and audio-only streams and merge them.
                // MP4 (H.264/AAC) is preferred for client compatibility; any container is the fallback.
                var videoStreams = manifest.GetVideoOnlyStreams().ToList();
                var audioStreams = manifest.GetAudioOnlyStreams().ToList();
                if (videoStreams.Count == 0 || audioStreams.Count == 0)
                {
                    _logger.LogWarning("|CinemaTrailers4Jellyfins| No usable video/audio streams for {Key}.", key);
                    return false;
                }

                var mp4Video = videoStreams.Where(s => s.Container == Container.Mp4).ToList();
                var video = PickByHeight(mp4Video.Count > 0 ? mp4Video : videoStreams, preferredHeight);
                var mp4Audio = audioStreams.Where(s => s.Container == Container.Mp4).ToList();
                var audio = (mp4Audio.Count > 0 ? mp4Audio : audioStreams).GetWithHighestBitrate();

                _logger.LogInformation(
                    "|CinemaTrailers4Jellyfins| Downloading {Key} at {Quality} (video + audio, merged with ffmpeg) to {Path}",
                    key, video.VideoQuality.Label, outputPath);

                await youtube.Videos.Streams.DownloadAsync(video, videoTemp, cancellationToken: ct).ConfigureAwait(false);
                await youtube.Videos.Streams.DownloadAsync(audio, audioTemp, cancellationToken: ct).ConfigureAwait(false);

                return await MergeAsync(key, videoTemp, audioTemp, outputPath, ct).ConfigureAwait(false);
            }
            catch (OperationCanceledException)
            {
                throw;
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "|CinemaTrailers4Jellyfins| YoutubeExplode download failed for {Key}", key);
                return false;
            }
            finally
            {
                TryDeleteFile(videoTemp);
                TryDeleteFile(audioTemp);
            }
        }

        // Highest quality at or below the configured height limit, else the lowest available.
        private static T PickByHeight<T>(System.Collections.Generic.IReadOnlyList<T> streams, int preferredHeight)
            where T : IVideoStreamInfo
            => streams
                .Where(s => s.VideoQuality.MaxHeight <= preferredHeight)
                .OrderByDescending(s => s.VideoQuality.MaxHeight)
                .FirstOrDefault()
               ?? streams.OrderBy(s => s.VideoQuality.MaxHeight).First();

        // Stream-copies (no re-encode) the video and audio tracks into one MP4.
        // Writes to a temp file first so a failed merge never leaves a broken trailer.
        private async Task<bool> MergeAsync(string key, string videoPath, string audioPath, string outputPath, CancellationToken ct)
        {
            var mergeTemp = outputPath + ".merge.tmp";
            try
            {
                var args = string.Join(" ",
                    "-y -loglevel error",
                    $"-i \"{videoPath}\"",
                    $"-i \"{audioPath}\"",
                    "-map 0:v:0 -map 1:a:0 -c copy -movflags +faststart",
                    "-f mp4",
                    $"\"{mergeTemp}\"");

                using var process = new Process
                {
                    StartInfo = new ProcessStartInfo
                    {
                        FileName = FfmpegLocator.Path,
                        Arguments = args,
                        RedirectStandardOutput = true,
                        RedirectStandardError = true,
                        UseShellExecute = false,
                        CreateNoWindow = true,
                    }
                };

                process.Start();
                // Drain both pipes while ffmpeg runs so a full buffer can never block it.
                var stdoutTask = process.StandardOutput.ReadToEndAsync(ct);
                var stderrTask = process.StandardError.ReadToEndAsync(ct);
                await process.WaitForExitAsync(ct).ConfigureAwait(false);
                await stdoutTask.ConfigureAwait(false);
                var stderr = await stderrTask.ConfigureAwait(false);

                if (process.ExitCode != 0 || !File.Exists(mergeTemp))
                {
                    _logger.LogError("|CinemaTrailers4Jellyfins| ffmpeg merge failed for {Key} (exit code {Code}): {Error}",
                        key, process.ExitCode, stderr);
                    return false;
                }

                File.Move(mergeTemp, outputPath, overwrite: true);
                return true;
            }
            finally
            {
                TryDeleteFile(mergeTemp);
            }
        }

        private void TryDeleteFile(string path)
        {
            try
            {
                if (File.Exists(path))
                    File.Delete(path);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "|CinemaTrailers4Jellyfins| Could not delete temporary file {Path}", path);
            }
        }

        private async Task<bool> DownloadWithYtDlpAsync(
            string key,
            string outputPath,
            int preferredHeight,
            string ytDlpPath,
            CancellationToken ct)
        {
            try
            {
                // Format selects the best video at or below preferredHeight merged with the best audio,
                // preferring H.264 + AAC (plays or hardware-transcodes on every client; VP9/AV1 often
                // need a CPU transcode). --merge-output-format mp4 ensures the output is always an mp4.
                var args = string.Join(" ",
                    $"-f \"bestvideo[height<={preferredHeight}][vcodec^=avc1]+bestaudio[ext=m4a]/bestvideo[height<={preferredHeight}]+bestaudio/best[height<={preferredHeight}]\"",
                    "--merge-output-format mp4",
                    "--no-playlist",
                    "--no-warnings",
                    "--no-progress",
                    $"--ffmpeg-location \"{FfmpegLocator.Path}\"",
                    $"-o \"{outputPath}\"",
                    $"\"https://www.youtube.com/watch?v={key}\"");

                _logger.LogInformation(
                    "|CinemaTrailers4Jellyfins| Downloading {Key} via yt-dlp at max {Height}p to {Path}",
                    key, preferredHeight, outputPath);

                using var process = new Process
                {
                    StartInfo = new ProcessStartInfo
                    {
                        FileName = ytDlpPath,
                        Arguments = args,
                        RedirectStandardOutput = true,
                        RedirectStandardError = true,
                        UseShellExecute = false,
                        CreateNoWindow = true,
                    }
                };

                process.Start();
                // Drain both pipes while yt-dlp runs so a full buffer can never block it.
                var stdoutTask = process.StandardOutput.ReadToEndAsync(ct);
                var stderrTask = process.StandardError.ReadToEndAsync(ct);
                await process.WaitForExitAsync(ct).ConfigureAwait(false);
                await stdoutTask.ConfigureAwait(false);
                var stderr = await stderrTask.ConfigureAwait(false);

                if (process.ExitCode != 0)
                {
                    _logger.LogError("|CinemaTrailers4Jellyfins| yt-dlp exited with code {Code} for {Key}: {Error}",
                        process.ExitCode, key, stderr);
                    return false;
                }

                return File.Exists(outputPath);
            }
            catch (OperationCanceledException)
            {
                throw;
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "|CinemaTrailers4Jellyfins| yt-dlp download failed for {Key}", key);
                return false;
            }
            finally
            {
                DeleteYtDlpLeftovers(outputPath);
            }
        }

        // yt-dlp names its separate/partial downloads "<output name>.f137.mp4.part", ".f140.m4a",
        // ".ytdl", ... It removes them after a successful merge, but not when it fails. Everything
        // sharing the output's "<name>." prefix (other than the output itself) is one of those.
        private void DeleteYtDlpLeftovers(string outputPath)
        {
            var folder = Path.GetDirectoryName(outputPath);
            if (folder == null || !Directory.Exists(folder))
                return;

            var outputName = Path.GetFileName(outputPath);
            var prefix = Path.GetFileNameWithoutExtension(outputPath) + ".";
            foreach (var file in Directory.EnumerateFiles(folder))
            {
                var name = Path.GetFileName(file);
                if (name.StartsWith(prefix, StringComparison.Ordinal)
                    && !string.Equals(name, outputName, StringComparison.Ordinal))
                {
                    TryDeleteFile(file);
                }
            }
        }
    }
}