Add mutable audience forwarder class

This class allows for ForwardingAudience-esque behaviour, while being mutable. It is currently not thread safe.

It was implemented as we need a good way to implement a "TransactionSpy" (or "EconomySpy", maybe) in the future, once we finalize planned administrative functions.

Patchwork/src/main/java/me/totalfreedom/audience/MutableAudienceForwarder.java

@@ -0,0 +1,244 @@
+package me.totalfreedom.audience;
+
+import net.kyori.adventure.audience.Audience;
+import net.kyori.adventure.bossbar.BossBar;
+import net.kyori.adventure.chat.ChatType;
+import net.kyori.adventure.chat.SignedMessage;
+import net.kyori.adventure.inventory.Book;
+import net.kyori.adventure.sound.Sound;
+import net.kyori.adventure.sound.SoundStop;
+import net.kyori.adventure.text.Component;
+import net.kyori.adventure.text.ComponentLike;
+import net.kyori.adventure.title.Title;
+import net.kyori.adventure.title.TitlePart;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+
+/**
+ * A replacement for {@link net.kyori.adventure.audience.ForwardingAudience} that allows for audiences to be removed & added at will. Not thread safe.
+ * <p>
+ * This is intended for use in toggleable logging systems, for example, potion spy.
+ */
+// TODO: Work on thread-safety (or thread-safe alternative)
+public class MutableAudienceForwarder implements Audience
+{
+    private final Set<Audience> audiences = new HashSet<>();
+
+    public static MutableAudienceForwarder from(Audience... audiences)
+    {
+        MutableAudienceForwarder audienceForwarder = new MutableAudienceForwarder();
+
+        for (Audience audience : audiences)
+        {
+            audienceForwarder.addAudience(audience);
+        }
+
+        return audienceForwarder;
+    }
+
+    public void addAudience(Audience audience)
+    {
+        if (audiences.contains(audience) || audience == this /* Protect against honest self-referential calls */)
+        {
+            return;
+        }
+
+        audiences.add(audience);
+    }
+
+    public boolean removeAudience(Audience audience)
+    {
+        return audiences.remove(audience);
+    }
+
+
+    @Override
+    public @NotNull Audience filterAudience(@NotNull Predicate<? super Audience> filter)
+    {
+        return audiences.stream()
+                .filter(filter)
+                .findFirst()
+                .orElseThrow();
+    }
+
+    @Override
+    public void forEachAudience(@NotNull Consumer<? super Audience> action)
+    {
+        audiences.forEach(action);
+    }
+
+    @Override
+    public void sendMessage(@NotNull ComponentLike message)
+    {
+        audiences.forEach(a -> a.sendMessage(message));
+    }
+
+    @Override
+    public void sendMessage(@NotNull Component message)
+    {
+        audiences.forEach(a -> a.sendMessage(message));
+    }
+
+    @Override
+    public void sendMessage(@NotNull Component message, ChatType.@NotNull Bound boundChatType)
+    {
+        audiences.forEach(a -> a.sendMessage(message, boundChatType));
+    }
+
+    @Override
+    public void sendMessage(@NotNull ComponentLike message, ChatType.@NotNull Bound boundChatType)
+    {
+        audiences.forEach(a -> a.sendMessage(message, boundChatType));
+    }
+
+    @Override
+    public void sendMessage(@NotNull SignedMessage signedMessage, ChatType.@NotNull Bound boundChatType)
+    {
+        audiences.forEach(a -> a.sendMessage(signedMessage, boundChatType));
+    }
+
+    @Override
+    public void deleteMessage(@NotNull SignedMessage signedMessage)
+    {
+        audiences.forEach(a -> a.deleteMessage(signedMessage));
+    }
+
+    @Override
+    public void deleteMessage(SignedMessage.@NotNull Signature signature)
+    {
+        audiences.forEach(a -> a.deleteMessage(signature));
+    }
+
+    // The methods below here will (probably) never be used, however it's good to keep them for completeness' sake.
+
+    @Override
+    public void sendActionBar(@NotNull ComponentLike message)
+    {
+        audiences.forEach(a -> a.sendActionBar(message));
+    }
+
+    @Override
+    public void sendActionBar(@NotNull Component message)
+    {
+        audiences.forEach(a -> a.sendActionBar(message));
+    }
+
+    @Override
+    public void sendPlayerListHeader(@NotNull ComponentLike header)
+    {
+        audiences.forEach(a -> a.sendPlayerListHeader(header));
+    }
+
+    @Override
+    public void sendPlayerListHeader(@NotNull Component header)
+    {
+        audiences.forEach(a -> a.sendPlayerListHeader(header));
+    }
+
+    @Override
+    public void sendPlayerListFooter(@NotNull ComponentLike footer)
+    {
+        audiences.forEach(a -> a.sendPlayerListFooter(footer));
+    }
+
+    @Override
+    public void sendPlayerListFooter(@NotNull Component footer)
+    {
+        audiences.forEach(a -> a.sendPlayerListFooter(footer));
+    }
+
+    @Override
+    public void sendPlayerListHeaderAndFooter(@NotNull ComponentLike header, @NotNull ComponentLike footer)
+    {
+        audiences.forEach(a -> a.sendPlayerListHeaderAndFooter(header, footer));
+    }
+
+    @Override
+    public void sendPlayerListHeaderAndFooter(@NotNull Component header, @NotNull Component footer)
+    {
+        audiences.forEach(a -> a.sendPlayerListHeaderAndFooter(header, footer));
+    }
+
+    @Override
+    public void showTitle(@NotNull Title title)
+    {
+        audiences.forEach(a -> a.showTitle(title));
+    }
+
+    @Override
+    public <T> void sendTitlePart(@NotNull TitlePart<T> part, @NotNull T value)
+    {
+        audiences.forEach(a -> a.sendTitlePart(part, value));
+    }
+
+    @Override
+    public void clearTitle()
+    {
+        audiences.forEach(Audience::clearTitle);
+    }
+
+    @Override
+    public void resetTitle()
+    {
+        audiences.forEach(Audience::resetTitle);
+    }
+
+    @Override
+    public void showBossBar(@NotNull BossBar bar)
+    {
+        audiences.forEach(a -> a.showBossBar(bar));
+    }
+
+    @Override
+    public void hideBossBar(@NotNull BossBar bar)
+    {
+        audiences.forEach(a -> a.hideBossBar(bar));
+    }
+
+    @Override
+    public void playSound(@NotNull Sound sound)
+    {
+        audiences.forEach(a -> a.playSound(sound));
+    }
+
+    @Override
+    public void playSound(@NotNull Sound sound, double x, double y, double z)
+    {
+
+        audiences.forEach(a -> a.playSound(sound, x, y, z));
+    }
+
+    @Override
+    public void playSound(@NotNull Sound sound, Sound.@NotNull Emitter emitter)
+    {
+        audiences.forEach(a -> a.playSound(sound, emitter));
+    }
+
+    @Override
+    public void stopSound(@NotNull Sound sound)
+    {
+        audiences.forEach(a -> a.stopSound(sound));
+    }
+
+    @Override
+    public void stopSound(@NotNull SoundStop stop)
+    {
+        audiences.forEach(a -> a.stopSound(stop));
+    }
+
+    @Override
+    public void openBook(Book.@NotNull Builder book)
+    {
+        audiences.forEach(a -> a.openBook(book));
+    }
+
+    @Override
+    public void openBook(@NotNull Book book)
+    {
+        audiences.forEach(a -> a.openBook(book));
+    }
+}