add EventManager

build.gradle

@@ -13,15 +13,34 @@ project.version = projectVersion
 repositories {
     mavenLocal()
     mavenCentral()
+    maven { url 'https://hub.spigotmc.org/nexus/content/groups/public' }
 }
 
 ext {
     libs = [
+            bukkit: [lib: 'org.bukkit:bukkit:1.12.2-R0.1-SNAPSHOT', exclude: [
+                    'com.google.code.gson:gson',
+                    'com.google.guava:guava',
+                    'com.googlecode.json-simple:json-simple',
+                    'commons-lang:commons-lang',
+                    'org.yaml:snakeyaml'
+            ]],
             lombok: 'org.projectlombok:lombok:1.18.12'
     ]
 }
 
+def compileOnly2(library) {
+    dependencies.compileOnly library.lib, {
+        library.exclude.each { String excludeLibStr ->
+            String[] excludeLib = excludeLibStr.split(':')
+            exclude group: excludeLib[0], module: excludeLib[1]
+        }
+    }
+}
+
 dependencies {
     compileOnly libs.lombok
     annotationProcessor libs.lombok
+
+    compileOnly2 libs.bukkit
 }

src/main/java/ghast/EventManager.java

@@ -0,0 +1,68 @@
+package ghast;
+
+import lombok.AccessLevel;
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+import lombok.Setter;
+import lombok.experimental.UtilityClass;
+import org.bukkit.Bukkit;
+import org.bukkit.event.Event;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+import org.bukkit.plugin.Plugin;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.BooleanSupplier;
+import java.util.function.Consumer;
+
+@UtilityClass
+@SuppressWarnings("unused")
+public class EventManager {
+
+	public Builder createContext(Plugin plugin) {
+		return new Builder(plugin);
+	}
+
+	@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
+	public static class Builder {
+
+		private static final BooleanSupplier EMPTY_FILTER = () -> true;
+
+		private final EventContext eventContext = new EventContext();
+		private final Plugin plugin;
+
+		public Builder filter(BooleanSupplier filter) {
+			eventContext.setFilter(filter != null ? filter : EMPTY_FILTER);
+			return this;
+		}
+
+		public <T extends Event> Builder onEvent(Class<T> eventType, EventPriority eventPriority, Consumer<T> consumer) {
+			eventContext.getEventMap().put(eventType, consumer);
+			Bukkit.getPluginManager().registerEvent(eventType, eventContext, eventPriority,
+					eventContext::eventExecute, plugin);
+			return this;
+		}
+
+		public <T extends Event> Builder onEvent(Class<T> eventType, Consumer<T> consumer) {
+			return onEvent(eventType, EventPriority.NORMAL, consumer);
+		}
+	}
+
+	@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
+	@Getter(AccessLevel.PRIVATE)
+	@Setter(AccessLevel.PRIVATE)
+	private static class EventContext implements Listener {
+
+		private final Map<Class<? extends Event>, Consumer<?>> eventMap = new HashMap<>();
+		private BooleanSupplier filter;
+
+		@SuppressWarnings({ "unchecked", "rawtypes" })
+		private void eventExecute(Listener listener, Event event) {
+			Consumer consumer = eventMap.get(event.getClass());
+			if (consumer != null && filter.getAsBoolean()) {
+				consumer.accept(event);
+			}
+		}
+	}
+}