sanePluginMessaging.java

	/**
	 * Sends a plugin message using the first player from {@link Bukkit#getOnlinePlayers()}.
	 *
	 * The next plugin message to be received through {@code channel} will be assumed to be
	 * the response.
	 *
	 * @param channel the channel for this plugin message
	 * @param data the data to add to the outgoing message
	 * @return a completable future for the message of the responding plugin message, if there is one.
	 * this completable future will complete exceptionally if no players are online.
	 */
	public static CompletableFuture<ByteArrayDataInput> sendPluginMessage(String channel, String... data) {
		return sendPluginMessage(channel, r -> true, data);
	}

	/**
	 * Sends a plugin message using the from {@code player}.
	 *
	 * The next plugin message to be received through {@code channel} will be assumed to be
	 * the response.
	 *
	 * @param player the player to send the plugin message through
	 * @param channel the channel for this plugin message
	 * @param data the data to add to the outgoing message
	 * @return a completable future for the message of the responding plugin message, if there is one.
	 * this completable future will complete exceptionally if no players are online.
	 */
	public static CompletableFuture<ByteArrayDataInput> sendPluginMessage(Player player, String channel, String... data) {
		return sendPluginMessage(player, channel, r -> true, data);
	}

	/**
	 * Sends a plugin message using the first player from {@link Bukkit#getOnlinePlayers()}.
	 *
	 * @param channel the channel for this plugin message
	 * @param messageVerifier verifies that a plugin message is the response to the sent message
	 * @param data the data to add to the outgoing message
	 * @return a completable future for the message of the responding plugin message, if there is one.
	 * this completable future will complete exceptionally if the player is null.
	 */
	public static CompletableFuture<ByteArrayDataInput> sendPluginMessage(String channel,
			Predicate<ByteArrayDataInput> messageVerifier, String... data) {
		Player firstPlayer = Iterables.getFirst(Bukkit.getOnlinePlayers(), null);
		return sendPluginMessage(firstPlayer, channel, messageVerifier, data);
	}

	/**
	 * Sends a plugin message.
	 *
	 * Example usage using the "GetServers" bungee plugin message channel via an overload:
	 * <code>
	 *     Utils.sendPluginMessage("BungeeCord", r -> "GetServers".equals(r.readUTF()), "GetServers")
	 *     			.thenAccept(response -> Bukkit.broadcastMessage(response.readUTF()) // comma delimited server broadcast
	 *     			.exceptionally(ex -> {
	 *     			 	Skript.warning("Failed to get servers because there are no players online");
	 *     			 	return null;
	 *     			});
	 * </code>
	 *
	 * @param player the player to send the plugin message through
	 * @param channel the channel for this plugin message
	 * @param messageVerifier verifies that a plugin message is the response to the sent message
	 * @param data the data to add to the outgoing message
	 * @return a completable future for the message of the responding plugin message, if there is one.
	 * this completable future will complete exceptionally if the player is null.
	 */
	public static CompletableFuture<ByteArrayDataInput> sendPluginMessage(Player player, String channel,
			Predicate<ByteArrayDataInput> messageVerifier, String... data) {
		CompletableFuture<ByteArrayDataInput> completableFuture = new CompletableFuture<>();

		if (player == null) {
			completableFuture.completeExceptionally(new IllegalStateException("Can't send plugin messages from a null player"));
			return completableFuture;
		}

		Bukkit.getMessenger().registerOutgoingPluginChannel(Skript.getInstance(), channel);

		Bukkit.getMessenger().registerIncomingPluginChannel(Skript.getInstance(), channel, new PluginMessageListener() {

			@Override
			public void onPluginMessageReceived(@Nullable String sendingChannel, @Nullable Player sendingPlayer,
					@Nullable byte[] message) {
				ByteArrayDataInput input = ByteStreams.newDataInput(message);
				if (channel.equals(sendingChannel) && sendingPlayer == player && !completableFuture.isDone()
						&& messageVerifier.test(input)) {
					completableFuture.complete(input);
					Bukkit.getMessenger().unregisterIncomingPluginChannel(Skript.getInstance(), channel, this);
				}
			}

		});

		ByteArrayDataOutput out = ByteStreams.newDataOutput();
		Stream.of(data).forEach(out::writeUTF);
		player.sendPluginMessage(Skript.getInstance(), channel, out.toByteArray());

		return completableFuture;
	}