Lunaris2.0/Bot/Handler/MusicPlayer/PlayCommand/PlayHandler.cs

using System.Collections.Immutable;
using Discord.WebSocket;
using Lunaris2.SlashCommand;
using MediatR;
using Lavalink4NET;
using Lavalink4NET.Events.Players;
using Lavalink4NET.Integrations.SponsorBlock;
using Lavalink4NET.Integrations.SponsorBlock.Extensions;
using Lavalink4NET.Players.Queued;
using Lavalink4NET.Rest.Entities.Tracks;
using Lavalink4NET.Tracks;

namespace Lunaris2.Handler.MusicPlayer.PlayCommand;

public record PlayCommand(SocketSlashCommand Message) : IRequest;

public class PlayHandler : IRequestHandler<PlayCommand>
{
    private readonly MusicEmbed _musicEmbed;
    private readonly DiscordSocketClient _client;
    private readonly IAudioService _audioService;
    private SocketSlashCommand _context;
    private const int MaxTrackDuration = 30;
    private LavalinkTrack? _previousTrack;
    private static readonly HashSet<ulong> SubscribedGuilds = new();
    
    public PlayHandler(
        DiscordSocketClient client, 
        MusicEmbed musicEmbed, 
        IAudioService audioService)
    {
        _client = client;
        _musicEmbed = musicEmbed;
        _audioService = audioService;
    }
    
    private async Task OnTrackEnded(object sender, TrackEndedEventArgs eventargs)
    {
        // Reset the previous track when the track ends.
        _previousTrack = null;
    }
    
    private async Task OnTrackStarted(object sender, TrackStartedEventArgs eventargs)
    {
        var player = sender as QueuedLavalinkPlayer;

        if (player?.CurrentTrack is null)
        {
            return; // No track is currently playing.
        }

        var currentTrack = player.CurrentTrack;

        // Check if the current track is the same as the previous one
        if (_previousTrack?.Identifier == currentTrack.Identifier)
        {
            // The same track is playing, so we don't need to create a new embed.
            return;
        }

        // Track has changed, update the previous track and send the embed
        _previousTrack = currentTrack;
        await _musicEmbed.NowPlayingEmbed(currentTrack, _context, _client);
    }
    
    public Task Handle(PlayCommand command, CancellationToken cancellationToken)
    {
        new Thread(PlayMusic).Start();
        return Task.CompletedTask;

        async void PlayMusic()
        {
            try
            {
                RegisterTrackStartedEventListerner(command);
                
                await _audioService.StartAsync(cancellationToken);
                
                var context = command.Message;
                _context = context;
                
                if ((context.User as SocketGuildUser)?.VoiceChannel == null)
                {
                    await context.SendMessageAsync("You must be in a voice channel to use this command.", _client);
                    return;
                }
                
                var searchQuery = context.GetOptionValueByName(Option.Input);

                if (string.IsNullOrWhiteSpace(searchQuery))
                {
                    await context.SendMessageAsync("Please provide search terms.", _client);
                    return;
                }
                
                await context.SendMessageAsync("📻 Searching...", _client);
                
                var player = await _audioService.GetPlayerAsync(_client, context, connectToVoiceChannel: true);
                
                if (player is null) 
                    return;
                
                await ApplyFilters(cancellationToken, player);
                await ConfigureSponsorBlock(cancellationToken, player);

                var trackLoadOptions = new TrackLoadOptions 
                { 
                    SearchMode = TrackSearchMode.YouTube, 
                };

                var trackCollection = await _audioService.Tracks.LoadTracksAsync(searchQuery, trackLoadOptions, cancellationToken: cancellationToken);

                // Check if the result is a playlist or just a single track from the search result
                if (trackCollection.IsPlaylist)
                {
                    // If it's a playlist, check if it's a free-text input.
                    if (!Uri.IsWellFormedUriString(searchQuery, UriKind.Absolute))
                    {
                        // Free text was used (not a direct URL to a playlist), let's prevent queueing the whole playlist.
                        // Queue only the first track of the search result
                        // var firstTrack = trackCollection.Tracks.FirstOrDefault();
                        if (trackCollection.Track != null)
                        {
                            await player.PlayAsync(trackCollection.Track, cancellationToken: cancellationToken).ConfigureAwait(false);
                            await _musicEmbed.NowPlayingEmbed(trackCollection.Track, _context, _client);
                        }
                        else
                        {
                            await context.SendMessageAsync("No tracks found.", _client);
                        }
                    }
                    else
                    {
                        // It's a playlist and a URL was used, so we can queue all tracks as usual
                        var queueTracks = trackCollection.Tracks
                            .Skip(1)
                            .Select(t => new TrackQueueItem(t))
                            .ToList();
                        
                        await player.PlayAsync(trackCollection.Tracks.First(), cancellationToken: cancellationToken).ConfigureAwait(false);
                        await player.Queue.AddRangeAsync(queueTracks, cancellationToken);
                        await context.SendMessageAsync($"Queued playlist {trackCollection.Playlist?.Name} with {queueTracks.Count} tracks.", _client);
                    }
                }
                else
                {
                    // It's just a single track or a search result.
                    var track = trackCollection.Tracks.FirstOrDefault();
    
                    if (track != null)
                    {
                        await player.PlayAsync(track, cancellationToken: cancellationToken).ConfigureAwait(false);
                        await _musicEmbed.NowPlayingEmbed(track, _context, _client);
                    }
                    else
                    {
                        await context.SendMessageAsync("No tracks found.", _client);
                    }
                }
            }
            catch (Exception error)
            {
                throw new Exception("Error occured in the Play handler!", error);
            }
        }
    }

    private void RegisterTrackStartedEventListerner(PlayCommand command)
    {
        if (SubscribedGuilds.Contains((ulong)command.Message.GuildId!)) 
            return;
        
        _audioService.TrackStarted += OnTrackStarted;
        _audioService.TrackEnded += OnTrackEnded;
        SubscribedGuilds.Add((ulong)command.Message.GuildId!);
    }

    private static async Task ApplyFilters(CancellationToken cancellationToken, QueuedLavalinkPlayer player)
    {
        var normalizationFilter = new NormalizationFilter(0.5, true);
        player.Filters.SetFilter(normalizationFilter);
        await player.Filters.CommitAsync(cancellationToken);
    }

    private static async Task ConfigureSponsorBlock(CancellationToken cancellationToken, QueuedLavalinkPlayer player)
    {
        var categories = ImmutableArray.Create(
            SegmentCategory.Intro,
            SegmentCategory.Sponsor,
            SegmentCategory.SelfPromotion,
            SegmentCategory.Outro,
            SegmentCategory.Filler);

        await player.UpdateSponsorBlockCategoriesAsync(categories, cancellationToken: cancellationToken);
    }
}