Overhaul event handling (designed by WetABQ#3417)

src/main/java/emu/grasscutter/plugin/PluginManager.java

@@ -3,9 +3,8 @@ package emu.grasscutter.plugin;
 import emu.grasscutter.Grasscutter;
 import emu.grasscutter.server.event.Event;
 import emu.grasscutter.server.event.EventHandler;
-import emu.grasscutter.server.event.Listener;
+import emu.grasscutter.server.event.HandlerPriority;
 import emu.grasscutter.utils.Utils;
-import org.reflections.Reflections;
 
 import java.io.File;
 import java.io.InputStreamReader;
@@ -15,13 +14,14 @@ import java.net.URLClassLoader;
 import java.util.*;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
+import java.util.stream.Stream;
 
 /**
  * Manages the server's plugins & the event system.
  */
 public final class PluginManager {
     private final Map<String, Plugin> plugins = new HashMap<>();
-    private final Map<Plugin, List<Listener>> listeners = new HashMap<>();
+    private final List<EventHandler<?>> listeners = new LinkedList<>();
     
     public PluginManager() {
         this.loadPlugins(); // Load all plugins from the plugins directory.
@@ -68,7 +68,7 @@ public final class PluginManager {
                         JarEntry entry = entries.nextElement();
                         if(entry.isDirectory() || !entry.getName().endsWith(".class")) continue;
                         String className = entry.getName().replace(".class", "").replace("/", ".");
-                        Class<?> clazz = loader.loadClass(className);
+                        loader.loadClass(className);
                     }
                     
                     Class<?> pluginClass = loader.loadClass(pluginConfig.mainClass);
@@ -129,11 +129,10 @@ public final class PluginManager {
 
     /**
      * Registers a plugin's event listener.
-     * @param plugin The plugin instance.
      * @param listener The event listener.
      */
-    public void registerListener(Plugin plugin, Listener listener) {
-        this.listeners.computeIfAbsent(plugin, k -> new ArrayList<>()).add(listener);
+    public void registerListener(EventHandler<?> listener) {
+        this.listeners.add(listener);
     }
     
     /**
@@ -141,23 +140,24 @@ public final class PluginManager {
      * @param event The event to invoke.
      */
     public void invokeEvent(Event event) {
-        this.listeners.values().stream()
-                .flatMap(Collection::stream)
-                .forEach(listener -> this.invokeOnListener(listener, event));
+        Stream<EventHandler<?>> handlers = this.listeners.stream()
+                .filter(handler -> event.getClass().isInstance(event));
+        handlers.filter(handler -> handler.getPriority() == HandlerPriority.HIGH)
+                .toList().forEach(handler -> this.invokeHandler(event, handler));
+        handlers.filter(handler -> handler.getPriority() == HandlerPriority.NORMAL)
+                .toList().forEach(handler -> this.invokeHandler(event, handler));
+        handlers.filter(handler -> handler.getPriority() == HandlerPriority.LOW)
+                .toList().forEach(handler -> this.invokeHandler(event, handler));
     }
-    
+
     /**
-     * Attempts to invoke the event on the provided listener.
+     * Performs logic checks then invokes the provided event handler.
+     * @param event The event passed through to the handler.
+     * @param handler The handler to invoke.
      */
-    private void invokeOnListener(Listener listener, Event event) {
-        try {
-            Class<?> listenerClass = listener.getClass();
-            Method[] methods = listenerClass.getMethods();
-            for (Method method : methods) {
-                if(!method.isAnnotationPresent(EventHandler.class)) return;
-                if(!method.getParameterTypes()[0].isAssignableFrom(event.getClass())) return;
-                method.invoke(listener, event);
-            }
-        } catch (Exception ignored) { }
+    private void invokeHandler(Event event, EventHandler<?> handler) {
+        if(!event.isCanceled() ||
+                (event.isCanceled() && handler.ignoresCanceled())
+        ) handler.getCallback().accept(event);
     }
 }

src/main/java/emu/grasscutter/server/event/EventHandler.java

@@ -1,11 +1,79 @@
 package emu.grasscutter.server.event;
 
-import java.lang.annotation.Retention;
-import java.lang.annotation.RetentionPolicy;
+import emu.grasscutter.Grasscutter;
 
-/**
- * Declares a class as an event listener/handler.
- */
-@Retention(RetentionPolicy.RUNTIME)
-public @interface EventHandler {
+import java.util.function.Consumer;
+
+public final class EventHandler<E extends Event> {
+    private E event;
+    
+    private Consumer<Event> listener;
+    private HandlerPriority priority;
+    private boolean handleCanceled;
+
+    /**
+     * Gets which event this handler is handling.
+     * @return An event class.
+     */
+    public Event handles() {
+        return this.event;
+    }
+
+    /**
+     * Returns the callback for the handler.
+     * @return A consumer callback.
+     */
+    public Consumer<Event> getCallback() {
+        return this.listener;
+    }
+
+    /**
+     * Returns the handler's priority.
+     * @return The priority of the handler.
+     */
+    public HandlerPriority getPriority() {
+        return this.priority;
+    }
+
+    /**
+     * Returns if the handler will ignore cancelled events.
+     * @return The ignore cancelled state.
+     */
+    public boolean ignoresCanceled() {
+        return this.handleCanceled;
+    }
+
+    /**
+     * Sets the callback method for when the event is invoked.
+     * @param listener An event handler method.
+     * @return Method chaining.
+     */
+    public EventHandler<E> listener(Consumer<Event> listener) {
+        this.listener = listener; return this;
+    }
+
+    /**
+     * Changes the handler's priority in handling events.
+     * @param priority The priority of the handler.
+     * @return Method chaining.
+     */
+    public EventHandler<E> priority(HandlerPriority priority) {
+        this.priority = priority; return this;
+    }
+
+    /**
+     * Sets if the handler will ignore cancelled events.
+     * @param ignore If the handler should ignore cancelled events.
+     * @return Method chaining.
+     */
+    public EventHandler<E> ignore(boolean ignore) {
+        this.handleCanceled = ignore; return this;
+    }
+
+    /**
+     * Registers the handler into the PluginManager.
+     */
+    public void register() {
+        Grasscutter.getPluginManager().registerListener(this);
+    }
 }

src/main/java/emu/grasscutter/server/event/HandlerPriority.java

@@ -0,0 +1,18 @@
+package emu.grasscutter.server.event;
+
+public enum HandlerPriority {
+    /**
+     * The handler will be called before every other handler.
+     */
+    HIGH,
+
+    /**
+     * The handler will be called the same time as other handlers.
+     */
+    NORMAL,
+
+    /**
+     * The handler will be called after every other handler.
+     */
+    LOW
+}

src/main/java/emu/grasscutter/server/event/Listener.java

@@ -1,7 +0,0 @@
-package emu.grasscutter.server.event;
-
-/**
- * Implementing this interface declares a class as an event listener.
- */
-public interface Listener {
-}