Implement simple event system

api/geyser/pom.xml

@@ -32,6 +32,12 @@
             <version>${adventure.version}</version>
             <scope>compile</scope>
         </dependency>
+        <dependency>
+            <groupId>net.kyori</groupId>
+            <artifactId>event-api</artifactId>
+            <version>3.0.0</version>
+            <scope>provided</scope>
+        </dependency>
         <dependency>
             <groupId>org.geysermc</groupId>
             <artifactId>base-api</artifactId>

api/geyser/src/main/java/org/geysermc/geyser/api/GeyserApi.java

@@ -30,6 +30,7 @@ import org.checkerframework.checker.nullness.qual.Nullable;
 import org.geysermc.api.Geyser;
 import org.geysermc.api.GeyserApiBase;
 import org.geysermc.geyser.api.connection.GeyserConnection;
+import org.geysermc.geyser.api.event.EventBus;
 import org.geysermc.geyser.api.extension.ExtensionManager;
 
 import java.util.List;
@@ -88,6 +89,14 @@ public interface GeyserApi extends GeyserApiBase {
      */
     ExtensionManager extensionManager();
 
+    /**
+     * Gets the {@link EventBus} for handling
+     * Geyser events.
+     *
+     * @return the event bus
+     */
+    EventBus eventBus();
+
     /**
      * Gets the current {@link GeyserApiBase} instance.
      *

api/geyser/src/main/java/org/geysermc/geyser/api/connection/GeyserConnection.java

@@ -28,7 +28,7 @@ package org.geysermc.geyser.api.connection;
 import org.geysermc.api.connection.Connection;
 
 /**
- * Represents a player session used in Geyser.
+ * Represents a player connection used in Geyser.
  */
 public interface GeyserConnection extends Connection {
 }

api/geyser/src/main/java/org/geysermc/geyser/api/event/Cancellable.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2019-2022 GeyserMC. http://geysermc.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.geyser.api.event;
+
+/**
+ * Represents a cancellable event.
+ */
+public interface Cancellable {
+
+    /**
+     * Gets if the event is cancelled.
+     *
+     * @return if the event is cancelled
+     */
+    boolean isCancelled();
+
+    /**
+     * Cancels the event.
+     *
+     * @param cancelled if the event is cancelled
+     */
+    void setCancelled(boolean cancelled);
+}

api/geyser/src/main/java/org/geysermc/geyser/api/event/Event.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2019-2022 GeyserMC. http://geysermc.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.geyser.api.event;
+
+/**
+ * Represents an event.
+ */
+public interface Event {
+
+    /**
+     * Gets if the event is async.
+     *
+     * @return if the event is async
+     */
+    default boolean isAsync() {
+        return false;
+    }
+}

api/geyser/src/main/java/org/geysermc/geyser/api/event/EventBus.java

@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2019-2022 GeyserMC. http://geysermc.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.geyser.api.event;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.geysermc.geyser.api.extension.Extension;
+
+import java.util.Set;
+import java.util.function.Consumer;
+
+/**
+ * Represents a bus capable of subscribing
+ * or "listening" to events and firing them.
+ */
+public interface EventBus {
+
+    /**
+     * Subscribes to the given event see {@link EventSubscription}.
+     *
+     * @param eventClass the class of the event
+     * @param consumer the consumer for handling the event
+     * @param <T> the event class
+     * @return the event subscription
+     */
+    @NonNull
+    <T extends Event> EventSubscription<T> subscribe(@NonNull Class<T> eventClass, @NonNull Consumer<? super T> consumer);
+
+    /**
+     * Subscribes to the given event see {@link EventSubscription}.
+     *
+     * The difference between this method and {@link #subscribe(Class, Consumer)}
+     * is that this method takes in an extension parameter which allows for
+     * the event to be unsubscribed upon extension disable and reloads.
+     *
+     * @param extension the extension to subscribe the event to
+     * @param eventClass the class of the event
+     * @param consumer the consumer for handling the event
+     * @param <T> the event class
+     * @return the event subscription
+     */
+    @NonNull
+    <T extends Event> EventSubscription<T> subscribe(@NonNull Extension extension, @NonNull Class<T> eventClass, @NonNull Consumer<? super T> consumer);
+
+    /**
+     * Unsubscribes the given {@link EventSubscription}.
+     *
+     * @param subscription the event subscription
+     */
+    <T extends Event> void unsubscribe(@NonNull EventSubscription<T> subscription);
+
+    /**
+     * Registers events for the given listener.
+     *
+     * @param extension the extension registering the event
+     * @param eventHolder the listener
+     */
+    void register(@NonNull Extension extension, @NonNull Object eventHolder);
+
+    /**
+     * Fires the given {@link Event}.
+     *
+     * @param event the event to fire
+     *
+     * @return true if the event successfully fired
+     */
+    boolean fire(@NonNull Event event);
+
+    /**
+     * Gets the subscriptions for the given event class.
+     *
+     * @param eventClass the event class
+     * @param <T> the value
+     * @return the subscriptions for the event class
+     */
+    @NonNull
+    <T extends Event> Set<EventSubscription<T>> subscriptions(@NonNull Class<T> eventClass);
+}

api/geyser/src/main/java/org/geysermc/geyser/api/event/EventSubscription.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright (c) 2019-2022 GeyserMC. http://geysermc.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.geyser.api.event;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.geysermc.geyser.api.extension.Extension;
+
+import java.util.function.Consumer;
+
+/**
+ * Represents a subscribed listener to a {@link Event}. Wraps around
+ * the event and is capable of unsubscribing from the event or give
+ * information about it.
+ *
+ * @param <T> the class of the event
+ */
+public interface EventSubscription<T extends Event> {
+
+    /**
+     * Gets the event class.
+     *
+     * @return the event class
+     */
+    @NonNull
+    Class<T> eventClass();
+
+    /**
+     * Gets the consumer responsible for handling
+     * this event.
+     *
+     * @return the consumer responsible for this event
+     */
+    @NonNull
+    Consumer<? super T> eventConsumer();
+
+    /**
+     * Gets the {@link Extension} that owns this
+     * event subscription.
+     *
+     * @return the extension that owns this subscription
+     */
+    @NonNull
+    Extension owner();
+
+    /**
+     * Gets the priority of this event subscription.
+     *
+     * @return the priority of this event subscription
+     */
+    Subscribe.Priority priority();
+
+    /**
+     * Gets if this event subscription is active.
+     *
+     * @return if this event subscription is active
+     */
+    boolean isActive();
+
+    /**
+     * Unsubscribes from this event listener
+     */
+    void unsubscribe();
+
+    /**
+     * Invokes the given event
+     *
+     * @param event the event
+     */
+    void invoke(@NonNull T event) throws Throwable;
+}

api/geyser/src/main/java/org/geysermc/geyser/api/event/Subscribe.java

@@ -0,0 +1,99 @@
+/*
+ * Copyright (c) 2019-2022 GeyserMC. http://geysermc.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.geyser.api.event;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.experimental.Accessors;
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * An annotation used to signify the given method is
+ * an {@link Event}. Only should be applied to methods
+ * where the class containing them is designated for
+ * events specifically.
+ *
+ * When using {@link EventBus#subscribe}, this annotation should
+ * not be applied whatsoever as it will have no use and potentially
+ * throw errors due to it being used wrongly.
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.METHOD)
+public @interface Subscribe {
+
+    /**
+     * The {@link Priority} of the event
+     *
+     * @return the priority of the event
+     */
+    @NonNull
+    Priority priority() default Priority.NORMAL;
+
+    /**
+     * Represents the priority of an event.
+     */
+    @Accessors(fluent = true)
+    @Getter
+    @AllArgsConstructor
+    enum Priority {
+
+        /**
+         * The lowest priority. Called first to
+         * allow for other events to customize
+         * the outcome
+         */
+        LOWEST(net.kyori.event.PostOrders.FIRST),
+
+        /**
+         * The second lowest priority.
+         */
+        LOW(net.kyori.event.PostOrders.EARLY),
+
+        /**
+         * Normal priority. Event is neither
+         * important nor unimportant
+         */
+        NORMAL(net.kyori.event.PostOrders.NORMAL),
+
+        /**
+         * The second highest priority
+         */
+        HIGH(net.kyori.event.PostOrders.LATE),
+
+        /**
+         * The highest of importance! Event is called
+         * last and has the final say in the outcome
+         */
+        HIGHEST(net.kyori.event.PostOrders.LAST);
+
+        private final int postOrder;
+    }
+}

api/geyser/src/main/java/org/geysermc/geyser/api/event/lifecycle/GeyserPostInitializeEvent.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2019-2022 GeyserMC. http://geysermc.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.geyser.api.event.lifecycle;
+
+import org.geysermc.geyser.api.event.Event;
+
+/**
+ * Called when Geyser has completed initializing.
+ */
+public class GeyserPostInitializeEvent implements Event {
+}

api/geyser/src/main/java/org/geysermc/geyser/api/event/lifecycle/GeyserShutdownEvent.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2019-2022 GeyserMC. http://geysermc.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.geyser.api.event.lifecycle;
+
+import org.geysermc.geyser.api.event.Event;
+
+/**
+ * Called when Geyser is shutting down.
+ */
+public class GeyserShutdownEvent implements Event {
+}

core/pom.xml

@@ -244,6 +244,13 @@
             <version>${adventure.version}</version>
             <scope>compile</scope>
         </dependency>
+        <!-- Kyori Misc -->
+        <dependency>
+            <groupId>net.kyori</groupId>
+            <artifactId>event-api</artifactId>
+            <version>3.0.0</version>
+            <scope>compile</scope>
+        </dependency>
         <!-- Other -->
         <dependency>
             <groupId>junit</groupId>

core/src/main/java/org/geysermc/geyser/GeyserImpl.java

@@ -49,9 +49,13 @@ import org.geysermc.floodgate.crypto.Base64Topping;
 import org.geysermc.floodgate.crypto.FloodgateCipher;
 import org.geysermc.floodgate.news.NewsItemAction;
 import org.geysermc.geyser.api.GeyserApi;
+import org.geysermc.geyser.api.event.EventBus;
+import org.geysermc.geyser.api.event.lifecycle.GeyserPostInitializeEvent;
+import org.geysermc.geyser.api.event.lifecycle.GeyserShutdownEvent;
 import org.geysermc.geyser.command.CommandManager;
 import org.geysermc.geyser.configuration.GeyserConfiguration;
 import org.geysermc.geyser.entity.EntityDefinitions;
+import org.geysermc.geyser.event.GeyserEventBus;
 import org.geysermc.geyser.extension.GeyserExtensionManager;
 import org.geysermc.geyser.level.WorldManager;
 import org.geysermc.geyser.network.ConnectorServerEventHandler;
@@ -123,6 +127,7 @@ public class GeyserImpl implements GeyserApi {
     private final PlatformType platformType;
     private final GeyserBootstrap bootstrap;
 
+    private final EventBus eventBus;
     private final GeyserExtensionManager extensionManager;
 
     private Metrics metrics;
@@ -158,6 +163,7 @@ public class GeyserImpl implements GeyserApi {
         MinecraftLocale.init();
 
         /* Load Extensions */
+        this.eventBus = new GeyserEventBus();
         this.extensionManager = new GeyserExtensionManager();
         this.extensionManager.init();
 
@@ -411,6 +417,8 @@ public class GeyserImpl implements GeyserApi {
         }
 
         newsHandler.handleNews(null, NewsItemAction.ON_SERVER_STARTED);
+
+        this.eventBus.fire(new GeyserPostInitializeEvent());
     }
 
     @Override
@@ -466,6 +474,8 @@ public class GeyserImpl implements GeyserApi {
 
         ResourcePack.PACKS.clear();
 
+        this.eventBus.fire(new GeyserShutdownEvent());
+
         this.extensionManager.disableExtensions();
 
         bootstrap.getGeyserLogger().info(GeyserLocale.getLocaleStringLog("geyser.core.shutdown.done"));
@@ -494,6 +504,11 @@ public class GeyserImpl implements GeyserApi {
         return this.extensionManager;
     }
 
+    @Override
+    public EventBus eventBus() {
+        return this.eventBus;
+    }
+
     public static GeyserImpl start(PlatformType platformType, GeyserBootstrap bootstrap) {
         if (instance == null) {
             return new GeyserImpl(platformType, bootstrap);

core/src/main/java/org/geysermc/geyser/event/GeyserEventBus.java

@@ -0,0 +1,110 @@
+/*
+ * Copyright (c) 2019-2022 GeyserMC. http://geysermc.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.geyser.event;
+
+import net.kyori.event.SimpleEventBus;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.geysermc.geyser.api.event.Event;
+import org.geysermc.geyser.api.event.EventBus;
+import org.geysermc.geyser.api.event.EventSubscription;
+import org.geysermc.geyser.api.event.Subscribe;
+import org.geysermc.geyser.api.extension.Extension;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.util.Set;
+import java.util.function.Consumer;
+import java.util.stream.Collectors;
+
+public class GeyserEventBus implements EventBus {
+    private final SimpleEventBus<Event> bus = new SimpleEventBus<>(Event.class);
+
+    @NonNull
+    @Override
+    public <T extends Event> EventSubscription<T> subscribe(@NonNull Class<T> eventClass, @NonNull Consumer<? super T> consumer) {
+        return this.subscribe(eventClass, consumer, null, Subscribe.Priority.NORMAL);
+    }
+
+    @NonNull
+    @Override
+    public <T extends Event> EventSubscription<T> subscribe(@NonNull Extension extension, @NonNull Class<T> eventClass, @NonNull Consumer<? super T> consumer) {
+        return this.subscribe(eventClass, consumer, extension, Subscribe.Priority.NORMAL);
+    }
+
+    @Override
+    public <T extends Event> void unsubscribe(@NonNull EventSubscription<T> subscription) {
+        this.bus.unregister((GeyserEventSubscription<T>) subscription);
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public void register(@NonNull Extension extension, @NonNull Object eventHolder) {
+        for (Method method : eventHolder.getClass().getMethods()) {
+            if (!method.isAnnotationPresent(Subscribe.class)) {
+                continue;
+            }
+
+            if (method.getParameterCount() > 1) {
+                continue;
+            }
+
+            if (!Event.class.isAssignableFrom(method.getParameters()[0].getType())) {
+                continue;
+            }
+
+            Subscribe subscribe = method.getAnnotation(Subscribe.class);
+            this.subscribe((Class<? extends Event>) method.getParameters()[0].getType(), (event) -> {
+                try {
+                    method.invoke(eventHolder, event);
+                } catch (IllegalAccessException | InvocationTargetException ex) {
+                    ex.printStackTrace();
+                }
+            }, extension, subscribe.priority());
+        }
+    }
+
+    @Override
+    public boolean fire(@NonNull Event event) {
+        return this.bus.post(event).wasSuccessful();
+    }
+
+    @SuppressWarnings("unchecked")
+    @NonNull
+    @Override
+    public <T extends Event> Set<EventSubscription<T>> subscriptions(@NonNull Class<T> eventClass) {
+        return bus.subscribers().values()
+                .stream()
+                .filter(sub -> sub instanceof EventSubscription && ((EventSubscription<?>) sub).eventClass().isAssignableFrom(eventClass))
+                .map(sub -> ((EventSubscription<T>) sub))
+                .collect(Collectors.toSet());
+    }
+
+    private <T extends Event> EventSubscription<T> subscribe(Class<T> eventClass, Consumer<? super T> handler, Extension extension, Subscribe.Priority priority) {
+        GeyserEventSubscription<T> eventSubscription = new GeyserEventSubscription<>(this, eventClass, handler, extension, priority);
+        this.bus.register(eventClass, eventSubscription);
+        return eventSubscription;
+    }
+}

core/src/main/java/org/geysermc/geyser/event/GeyserEventSubscription.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2019-2022 GeyserMC. http://geysermc.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.geyser.event;
+
+import lombok.AccessLevel;
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+import lombok.experimental.Accessors;
+import net.kyori.event.EventSubscriber;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.geysermc.geyser.api.event.Event;
+import org.geysermc.geyser.api.event.EventBus;
+import org.geysermc.geyser.api.event.EventSubscription;
+import org.geysermc.geyser.api.event.Subscribe;
+import org.geysermc.geyser.api.extension.Extension;
+
+import java.util.function.Consumer;
+
+@Getter
+@Accessors(fluent = true)
+@RequiredArgsConstructor
+public class GeyserEventSubscription<T extends Event> implements EventSubscription<T>, EventSubscriber<T> {
+    private final EventBus eventBus;
+    private final Class<T> eventClass;
+    private final Consumer<? super T> eventConsumer;
+    private final Extension owner;
+    private final Subscribe.Priority priority;
+    @Getter(AccessLevel.NONE) private boolean active;
+
+    @Override
+    public boolean isActive() {
+        return this.active;
+    }
+
+    @Override
+    public void unsubscribe() {
+        if (!this.active) {
+            return;
+        }
+
+        this.active = false;
+        this.eventBus.unsubscribe(this);
+    }
+
+    @Override
+    public void invoke(@NonNull T event) throws Throwable {
+        try {
+            this.eventConsumer.accept(event);
+        } catch (Throwable ex) {
+            this.owner.logger().warning("Unable to fire event " + event.getClass().getSimpleName() + " with subscription " + this.eventConsumer.getClass().getSimpleName());
+            ex.printStackTrace();
+        }
+    }
+
+    @Override
+    public int postOrder() {
+        return this.priority.postOrder();
+    }
+}