add EventManager

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);
+			}
+		}
+	}
+}