DynamicGuardSelector.java

/*******************************************************************************
 * Copyright 2014 See AUTHORS file.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ******************************************************************************/

package com.badlogic.gdx.ai.btree.branch;

import com.badlogic.gdx.ai.btree.BranchTask;
import com.badlogic.gdx.ai.btree.Task;
import com.badlogic.gdx.utils.Array;

/** A {@code DynamicGuardSelector} is a branch task that executes the first child whose guard is evaluated to {@code true}. At
 * every AI cycle, the children's guards are re-evaluated, so if the guard of the running child is evaluated to {@code false}, it
 * is cancelled, and the child with the highest priority starts running. The {@code DynamicGuardSelector} task finishes when no
 * guard is evaluated to {@code true} (thus failing) or when its active child finishes (returning the active child's termination
 * status).
 * 
 * @param <E> type of the blackboard object that tasks use to read or modify game state
 * 
 * @author davebaol */
public class DynamicGuardSelector<E> extends BranchTask<E> {

	/** The child in the running status or {@code null} if no child is running. */
	protected Task<E> runningChild;

	/** Creates a {@code DynamicGuardSelector} branch with no children. */
	public DynamicGuardSelector () {
		super();
	}

	/** Creates a {@code DynamicGuardSelector} branch with the given children.
	 * 
	 * @param tasks the children of this task */
	public DynamicGuardSelector (Task<E>... tasks) {
		super(new Array<Task<E>>(tasks));
	}

	/** Creates a {@code DynamicGuardSelector} branch with the given children.
	 * 
	 * @param tasks the children of this task */
	public DynamicGuardSelector (Array<Task<E>> tasks) {
		super(tasks);
	}

	@Override
	public void childRunning (Task<E> task, Task<E> reporter) {
		runningChild = task;
		running(); // Return a running status when a child says it's running
	}

	@Override
	public void childSuccess (Task<E> task) {
		this.runningChild = null;
		success();
	}

	@Override
	public void childFail (Task<E> task) {
		this.runningChild = null;
		fail();
	}

	@Override
	public void run () {
		// Check guards
		Task<E> childToRun = null;
		for (int i = 0, n = children.size; i < n; i++) {
			Task<E> child = children.get(i);
			if (child.checkGuard(this)) {
				childToRun = child;
				break;
			}
		}

		if (runningChild != null && runningChild != childToRun) {
			runningChild.cancel();
			runningChild = null;
		}
		if (childToRun == null) {
			fail();
		} else {
			if (runningChild == null) {
				runningChild = childToRun;
				runningChild.setControl(this);
				runningChild.start();
			}
			runningChild.run();
		}
	}

	@Override
	public void reset () {
		super.reset();
		this.runningChild = null;
	}

	@Override
	protected Task<E> copyTo (Task<E> task) {
		DynamicGuardSelector<E> branch = (DynamicGuardSelector<E>)task;
		branch.runningChild = null;

		return super.copyTo(task);
	}

}