Plugin-specific listeners & dependency loading

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

 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.HandlerPriority;
+import emu.grasscutter.server.event.*;
 import emu.grasscutter.utils.Utils;
+import lombok.*;
 
-import java.io.File;
-import java.io.FileNotFoundException;
-import java.io.InputStreamReader;
+import javax.annotation.Nullable;
+import java.io.*;
 import java.lang.reflect.Method;
-import java.net.MalformedURLException;
-import java.net.URL;
-import java.net.URLClassLoader;
+import java.net.*;
 import java.util.*;
-import java.util.jar.JarEntry;
-import java.util.jar.JarFile;
+import java.util.jar.*;
 
-import static emu.grasscutter.Configuration.*;
+import static emu.grasscutter.Configuration.PLUGIN;
 
 /**
  * Manages the server's plugins and the event system.
  */
 public final class PluginManager {
-    private final Map<String, Plugin> plugins = new HashMap<>();
-    private final List<EventHandler<? extends Event>> listeners = new LinkedList<>();
-    
+    /* All loaded plugins. */
+    private final Map<String, Plugin> plugins = new LinkedHashMap<>();
+    /* All currently registered listeners per plugin. */
+    private final Map<Plugin, List<EventHandler<? extends Event>>> listeners = new LinkedHashMap<>();
+
     public PluginManager() {
         this.loadPlugins(); // Load all plugins from the plugins directory.
     }
 
+    /* Data about an unloaded plugin. */
+    @AllArgsConstructor @Getter
+    static class PluginData {
+        private Plugin plugin;
+        private PluginIdentifier identifier;
+        private URLClassLoader classLoader;
+        private String[] dependencies;
+    }
+
     /**
      * Loads plugins from the config-specified directory.
      */
     private void loadPlugins() {
         File pluginsDir = new File(Utils.toFilePath(PLUGIN()));
-        if(!pluginsDir.exists() && !pluginsDir.mkdirs()) {
+        if (!pluginsDir.exists() && !pluginsDir.mkdirs()) {
             Grasscutter.getLogger().error("Failed to create plugins directory: " + pluginsDir.getAbsolutePath());
             return;
         }
-        
+
         File[] files = pluginsDir.listFiles();
-        if(files == null) {
+        if (files == null) {
             // The directory is empty, there aren't any plugins to load.
             return;
         }
-        
+
         List<File> plugins = Arrays.stream(files)
-                .filter(file -> file.getName().endsWith(".jar"))
-                .toList();
+            .filter(file -> file.getName().endsWith(".jar"))
+            .toList();
 
         URL[] pluginNames = new URL[plugins.size()];
         plugins.forEach(plugin -> {
@@ -59,36 +65,59 @@ public final class PluginManager {
             }
         });
 
+        // Create a class loader for the plugins.
         URLClassLoader classLoader = new URLClassLoader(pluginNames);
+        // Create a list of plugins that require dependencies.
+        List<PluginData> dependencies = new ArrayList<>();
 
-        plugins.forEach(plugin -> {
+        // Initialize all plugins.
+        for(var plugin : plugins) {
             try {
                 URL url = plugin.toURI().toURL();
                 try (URLClassLoader loader = new URLClassLoader(new URL[]{url})) {
-                    URL configFile = loader.findResource("plugin.json"); // Find the plugin.json file for each plugin.
+                    // Find the plugin.json file for each plugin.
+                    URL configFile = loader.findResource("plugin.json");
+                    // Open the config file for reading.
                     InputStreamReader fileReader = new InputStreamReader(configFile.openStream());
 
+                    // Create a plugin config instance from the config file.
                     PluginConfig pluginConfig = Grasscutter.getGsonFactory().fromJson(fileReader, PluginConfig.class);
-                    if(!pluginConfig.validate()) {
+                    // Check if the plugin config is valid.
+                    if (!pluginConfig.validate()) {
                         Utils.logObject(pluginConfig);
                         Grasscutter.getLogger().warn("Plugin " + plugin.getName() + " has an invalid config file.");
                         return;
                     }
 
+                    // Create a JAR file instance from the plugin's URL.
                     JarFile jarFile = new JarFile(plugin);
+                    // Load all class files from the JAR file.
                     Enumeration<JarEntry> entries = jarFile.entries();
-                    while(entries.hasMoreElements()) {
+                    while (entries.hasMoreElements()) {
                         JarEntry entry = entries.nextElement();
-                        if(entry.isDirectory() || !entry.getName().endsWith(".class") || entry.getName().contains("module-info")) continue;
+                        if (entry.isDirectory() || !entry.getName().endsWith(".class") || entry.getName().contains("module-info"))
+                            continue;
                         String className = entry.getName().replace(".class", "").replace("/", ".");
                         classLoader.loadClass(className); // Use the same class loader for ALL plugins.
                     }
-                    
+
+                    // Create a plugin instance.
                     Class<?> pluginClass = classLoader.loadClass(pluginConfig.mainClass);
                     Plugin pluginInstance = (Plugin) pluginClass.getDeclaredConstructor().newInstance();
+                    // Close the file reader.
+                    fileReader.close();
+
+                    // Check if the plugin has alternate dependencies.
+                    if(pluginConfig.loadAfter.length > 0) {
+                        // Add the plugin to a "load later" list.
+                        dependencies.add(new PluginData(
+                            pluginInstance, PluginIdentifier.fromPluginConfig(pluginConfig),
+                            loader, pluginConfig.loadAfter));
+                        continue;
+                    }
+
+                    // Load the plugin.
                     this.loadPlugin(pluginInstance, PluginIdentifier.fromPluginConfig(pluginConfig), loader);
-                    
-                    fileReader.close(); // Close the file reader.
                 } catch (ClassNotFoundException ignored) {
                     Grasscutter.getLogger().warn("Plugin " + plugin.getName() + " has an invalid main class.");
                 } catch (FileNotFoundException ignored) {
@@ -97,29 +126,58 @@ public final class PluginManager {
             } catch (Exception exception) {
                 Grasscutter.getLogger().error("Failed to load plugin: " + plugin.getName(), exception);
             }
-        });
+        }
+
+        // Load plugins with dependencies.
+        int depth = 0; final int maxDepth = 30;
+        while(!dependencies.isEmpty() || depth < maxDepth) {
+            try {
+                // Get the next plugin to load.
+                var pluginData = dependencies.get(0);
+                // Check if the plugin's dependencies are loaded.
+                if(!this.plugins.keySet().containsAll(List.of(pluginData.getDependencies()))) {
+                    depth++; // Increase depth counter.
+                    continue; // Continue to next plugin.
+                }
+
+                // Load the plugin.
+                this.loadPlugin(pluginData.getPlugin(), pluginData.getIdentifier(), pluginData.getClassLoader());
+            } catch (Exception exception) {
+                Grasscutter.getLogger().error("Failed to load a plugin.", exception);
+            }
+        }
     }
 
     /**
      * Load the specified plugin.
+     *
      * @param plugin The plugin instance.
      */
     private void loadPlugin(Plugin plugin, PluginIdentifier identifier, URLClassLoader classLoader) {
         Grasscutter.getLogger().info("Loading plugin: " + identifier.name);
-        
+
         // Add the plugin's identifier.
         try {
             Class<Plugin> pluginClass = Plugin.class;
             Method method = pluginClass.getDeclaredMethod("initializePlugin", PluginIdentifier.class, URLClassLoader.class);
-            method.setAccessible(true); method.invoke(plugin, identifier, classLoader); method.setAccessible(false);
+            method.setAccessible(true);
+            method.invoke(plugin, identifier, classLoader);
+            method.setAccessible(false);
         } catch (Exception ignored) {
             Grasscutter.getLogger().warn("Failed to add plugin identifier: " + identifier.name);
         }
-        
+
         // Add the plugin to the list of loaded plugins.
         this.plugins.put(identifier.name, plugin);
+        // Create a collection for the plugin's listeners.
+        this.listeners.put(plugin, new LinkedList<>());
+
         // Call the plugin's onLoad method.
-        plugin.onLoad();
+        try {
+            plugin.onLoad();
+        } catch (Exception exception) {
+            Grasscutter.getLogger().error("Failed to load plugin: " + identifier.name, exception);
+        }
     }
 
     /**
@@ -128,62 +186,121 @@ public final class PluginManager {
     public void enablePlugins() {
         this.plugins.forEach((name, plugin) -> {
             Grasscutter.getLogger().info("Enabling plugin: " + name);
-            plugin.onEnable();
+            try {
+                plugin.onEnable();
+            } catch (Exception exception) {
+                Grasscutter.getLogger().error("Failed to enable plugin: " + name, exception);
+            }
         });
     }
-    
+
     /**
      * Disables all registered plugins.
      */
     public void disablePlugins() {
         this.plugins.forEach((name, plugin) -> {
             Grasscutter.getLogger().info("Disabling plugin: " + name);
-            plugin.onDisable();
+            try {
+                plugin.onDisable();
+            } catch (Exception exception) {
+                Grasscutter.getLogger().error("Failed to disable plugin: " + name, exception);
+            }
         });
     }
 
     /**
      * Registers a plugin's event listener.
+     *
+     * @param plugin The plugin registering the listener.
      * @param listener The event listener.
      */
-    public void registerListener(EventHandler<? extends Event> listener) {
-        this.listeners.add(listener);
+    public void registerListener(Plugin plugin, EventHandler<? extends Event> listener) {
+        this.listeners.get(plugin).add(listener);
     }
-    
+
     /**
      * Invoke the provided event on all registered event listeners.
+     *
      * @param event The event to invoke.
      */
     public void invokeEvent(Event event) {
         EnumSet.allOf(HandlerPriority.class)
-                .forEach(priority -> this.checkAndFilter(event, priority));
+            .forEach(priority -> this.checkAndFilter(event, priority));
     }
 
     /**
      * Check an event to handlers for the priority.
-     * @param event The event being called.
+     *
+     * @param event    The event being called.
      * @param priority The priority to call for.
      */
     private void checkAndFilter(Event event, HandlerPriority priority) {
-        this.listeners.stream()
-                .filter(handler -> handler.handles().isInstance(event))
-                .filter(handler -> handler.getPriority() == priority)
-                .toList().forEach(handler -> this.invokeHandler(event, handler));
+        // Create a collection of listeners.
+        List<EventHandler<? extends Event>> listeners = new LinkedList<>();
+
+        // Add all listeners from every plugin.
+        this.listeners.values().forEach(listeners::addAll);
+
+        listeners.stream()
+            // Filter the listeners by priority.
+            .filter(handler -> handler.handles().isInstance(event))
+            .filter(handler -> handler.getPriority() == priority)
+            // Invoke the event.
+            .toList().forEach(handler -> this.invokeHandler(event, handler));
     }
 
+    /**
+     * Gets a plugin's instance by its name.
+     *
+     * @param name The name of the plugin.
+     * @return Either null, or the plugin's instance.
+     */
+    @Nullable
     public Plugin getPlugin(String name) {
         return this.plugins.get(name);
     }
 
+    /**
+     * Enables a plugin.
+     *
+     * @param plugin The plugin to enable.
+     */
+    public void enablePlugin(Plugin plugin) {
+        try {
+            // Call the plugin's onEnable method.
+            plugin.onEnable();
+        } catch (Exception exception) {
+            Grasscutter.getLogger().error("Failed to enable plugin: " + plugin.getName(), exception);
+        }
+    }
+
+    /**
+     * Disables a plugin.
+     *
+     * @param plugin The plugin to disable.
+     */
+    public void disablePlugin(Plugin plugin) {
+        try {
+            // Call the plugin's onDisable method.
+            plugin.onDisable();
+        } catch (Exception exception) {
+            Grasscutter.getLogger().error("Failed to disable plugin: " + plugin.getName(), exception);
+        }
+
+        // Un-register all listeners.
+        this.listeners.remove(plugin);
+    }
+
     /**
      * Performs logic checks then invokes the provided event handler.
-     * @param event The event passed through to the handler.
+     *
+     * @param event   The event passed through to the handler.
      * @param handler The handler to invoke.
      */
     @SuppressWarnings("unchecked")
     private <T extends Event> void invokeHandler(Event event, EventHandler<T> handler) {
-        if(!event.isCanceled() ||
-                (event.isCanceled() && handler.ignoresCanceled())
+        if (!event.isCanceled() ||
+            (event.isCanceled() && handler.ignoresCanceled())
         ) handler.getCallback().consume((T) event);
     }
 }