public final class ExampleBot {

  public static void main(final String[] args) {
    final String token = args[0];
    final DiscordClient client = DiscordClient.create(token);
    final GatewayDiscordClient gateway = client.login().block();

    gateway.on(MessageCreateEvent.class).subscribe(event -> {
      final Message message = event.getMessage();
      if ("!ping".equals(message.getContent())) {
        final MessageChannel channel = message.getChannel().block();
        channel.createMessage("Pong!").block();
      }
    });

    gateway.onDisconnect().block();
  }
}

repositories {
  mavenCentral()
}

dependencies {
  implementation 'com.discord4j:discord4j-core:3.1.2'
}

repositories {
  mavenCentral()
}

dependencies {
  implementation("com.discord4j:discord4j-core:3.1.2")
}

<dependencies>
  <dependency>
    <groupId>com.discord4j</groupId>
    <artifactId>discord4j-core</artifactId>
    <version>3.1.2</version>
  </dependency>
</dependencies>

libraryDependencies ++= Seq(
  "com.discord4j" % "discord4j-core" % "3.1.2"
)

public final class ExampleBot {

  public static void main(final String[] args) {
    final String token = args[0];
    final DiscordClient client = DiscordClient.create(token);

    client.login().flatMapMany(gateway -> gateway.on(MessageCreateEvent.class))
      .map(MessageCreateEvent::getMessage)
      .filter(message -> "!ping".equals(message.getContent()))
      .flatMap(Message::getChannel)
      .flatMap(channel -> channel.createMessage("Pong!"))
      .blockLast();
  }
}

final String token = args[0];
final DiscordClient client = DiscordClient.create(token);

client.withGateway(gateway -> {
  final Publisher<?> pingPong = gateway.on(MessageCreateEvent.class, event ->
    Mono.just(event.getMessage())
      .filter(message -> "!ping".equals(message.getContent()))
      .flatMap(Message::getChannel)
      .flatMap(channel -> channel.createMessage("Pong!")));
            
    final Publisher<?> onDisconnect = gateway.onDisconnect()
      .doOnTerminate(() -> System.out.println("Disconnected!"));

    return Mono.when(pingPong, onDisconnect);
  }).block();

val token = args[0]
val client = DiscordClient.create(token)

client.withGateway {
  mono {
    it.on(MessageCreateEvent::class.java)
      .asFlow()
      .collect {
        val message = it.message
        if (message.content == "!ping") {
          val channel = message.channel.awaitSingle()
          channel.createMessage("Pong!").awaitSingle()
        }
      }
  }
}
.block()

// IMAGE_URL = https://cdn.betterttv.net/emote/55028cd2135896936880fdd7/3x
// ANY_URL = https://www.youtube.com/watch?v=5zwY50-necw
final MessageChannel channel = ...
channel.createEmbed(spec -> 
  spec.setColor(Color.RED)
    .setAuthor("setAuthor", ANY_URL, IMAGE_URL)
    .setImage(IMAGE_URL)
    .setTitle("setTitle/setUrl")
    .setUrl(ANY_URL)
    .setDescription("setDescription\n" +
      "big D: is setImage\n" +
      "small D: is setThumbnail\n" +
      "<-- setColor")
    .addField("addField", "inline = true", true)
    .addField("addFIeld", "inline = true", true)
    .addField("addFile", "inline = false", false)
    .setThumbnail(IMAGE_URL)
    .setFooter("setFooter --> setTimestamp", IMAGE_URL)
    .setTimestamp(Instant.now())
).block();

final Guild guild = ...
final Set<Member> roleMembers = new HashSet<>();

for (final Member member : guild.getMembers().toIterable()) {
  for (final Role role : member.getRoles().toIterable()) {
    if ("Developers".equalsIgnoreCase(role.getName())) {
      roleMembers.add(member);
      break;
    }
  }
}

return roleMembers;

final Guild guild = ...
return guild.getMembers()
  .filterWhen(member -> member.getRoles()
    .map(Role::getName)
    .any("Developers"::equalsIgnoreCase));

public static final AudioPlayerManager PLAYER_MANAGER;

static {
  PLAYER_MANAGER = new DefaultAudioPlayerManager();
  // This is an optimization strategy that Discord4J can utilize to minimize allocations
  PLAYER_MANAGER.getConfiguration().setFrameBufferFactory(NonAllocatingAudioFrameBuffer::new);
  AudioSourceManagers.registerRemoteSources(PLAYER_MANAGER);
  AudioSourceManagers.registerLocalSource(PLAYER_MANAGER);
}

public final class LavaPlayerAudioProvider extends AudioProvider {

  private final AudioPlayer player;
  private final MutableAudioFrame frame;

  public LavaPlayerAudioProvider(final AudioPlayer player) {
    // Allocate a ByteBuffer for Discord4J's AudioProvider to hold audio data for Discord
    super(ByteBuffer.allocate(StandardAudioDataFormats.DISCORD_OPUS.maximumChunkSize()));
    // Set LavaPlayer's AudioFrame to use the same buffer as Discord4J's
    frame = new MutableAudioFrame();
    frame.setBuffer(getBuffer());
    this.player = player;
  }

  @Override
  public boolean provide() {
    // AudioPlayer writes audio data to the AudioFrame
    final boolean didProvide = player.provide(frame);

    if (didProvide) {
      getBuffer().flip();
    }

    return didProvide;
  }
}

public final class AudioTrackScheduler extends AudioEventAdapter {

  private final List<AudioTrack> queue;
  private final AudioPlayer player;

  public AudioTrackScheduler(final AudioPlayer player) {
    // The queue may be modifed by different threads so guarantee memory safety
    // This does not, however, remove several race conditions currently present
    queue = Collections.synchronizedList(new LinkedList<>());
    this.player = player;
  }

  public List<AudioTrack> getQueue() {
    return queue;
  }

  public boolean play(final AudioTrack track) {
    return play(track, false);
  }

  public boolean play(final AudioTrack track, final boolean force) {
    final boolean playing = player.startTrack(track, !force);

    if (!playing) {
      queue.add(track);
    }

    return playing;
  }

  public boolean skip() {
    return !queue.isEmpty() && play(queue.remove(0), true);
  }

  @Override
  public void onTrackEnd(final AudioPlayer player, final AudioTrack track, final AudioTrackEndReason endReason) {
    // Advance the player if the track completed naturally (FINISHED) or if the track cannot play (LOAD_FAILED)
    if (endReason.mayStartNext) {
      skip();
    }
  }
}

public final class GuildAudioManager {

  private static final Map<Snowflake, GuildAudioManager> MANAGERS = new ConcurrentHashMap<>();

  public static GuildAudioManager of(final Snowflake id) {
    return MANAGERS.computeIfAbsent(id, ignored -> new GuildAudioManager());
  }

  private final AudioPlayer player;
  private final AudioTrackScheduler scheduler;
  private final LavaPlayerAudioProvider provider;

  private GuildAudioManager() {
    player = PLAYER_MANAGER.createPlayer();
    scheduler = new AudioTrackScheduler(player);
    provider = new LavaPlayerAudioProvider(player);

    player.addListener(scheduler);
  }

  // getters
}

final VoiceChannel channel = ...
final AudioProvider provider = GuildAudioManager.of(channel.getGuildId()).getProvider();
final VoiceConnection connection = channel.join(spec -> spec.setProvider(provider)).block();

// In the AudioLoadResultHandler, add AudioTrack instances to the AudioTrackScheduler (and send notifications to users)
PLAYER_MANAGER.loadItem("https://www.youtube.com/watch?v=dQw4w9WgXcQ", new AudioLoadResultHandler() { /* overrides */ })

final VoiceChannel channel = ...
final Mono<Void> onDisconnect = channel.join(spec -> { /* TODO Initialize */ })
  .flatMap(connection -> {
    // The bot itself has a VoiceState; 1 VoiceState signals bot is alone
    final Publisher<Boolean> voiceStateCounter = channel.getVoiceStates()
      .count()
      .map(count -> 1L == count);

    // After 10 seconds, check if the bot is alone. This is useful if
    // the bot joined alone, but no one else joined since connecting
    final Mono<Void> onDelay = Mono.delay(Duration.ofSeconds(10L))
      .filterWhen(ignored -> voiceStateCounter)
      .switchIfEmpty(Mono.never())
      .then();

    // As people join and leave `channel`, check if the bot is alone.
    // Note the first filter is not strictly necessary, but it does prevent many unnecessary cache calls
    final Mono<Void> onEvent = channel.getClient().getEventDispatcher().on(VoiceStateUpdateEvent.class)
      .filter(event -> event.getOld().flatMap(VoiceState::getChannelId).map(channel.getId()::equals).orElse(false))
      .filterWhen(ignored -> voiceStateCounter)
      .next()
      .then();

    // Disconnect the bot if either onDelay or onEvent are completed!
    return Mono.first(onDelay, onEvent).then(connection.disconnect());
  });