org.jamesii.mlrules.observation.Observer Maven / Gradle / Ivy

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/*
 *   Copyright 2015 University of Rostock
 *
 *   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 org.jamesii.mlrules.observation;

import org.jamesii.mlrules.simulator.Simulator;

import java.util.HashSet;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Collectors;

/**
 * An observer observes the simulator, collects data and informs listener if
 * necessary. The observer must decide when to extract data (e.g., depending on
 * the number of steps) and how to format data (e.g., aggregate and filter
 * species). The observer is not doing something with the data (e.g., save the
 * data). This is the task of a listener.
 * 
 * @author Tobias Helms
 *
 */
public abstract class Observer {

	private Set listeners = new HashSet<>();

	public void register(Listener l) {
		listeners.add(l);
	}

	public boolean remove(Listener l) {
		return listeners.remove(l);
	}

	/**
	 * Notify all listener about the current observation. Remove all inactive
	 * listener from the listener set.
	 */
	public void notifyListener() {
		removeInactiveListeners();
		listeners.forEach(l -> l.notify(this));
	}
	
	/**
	 * Removes all inactive listeners from the listener set.
	 */
	private void removeInactiveListeners(){
		this.listeners = this.listeners.stream().filter( l -> l.isActive()).collect(Collectors.toSet());
	}

	/**
	 * Extract data from the simulator to update the current observation data.
	 */
	public abstract void update(Simulator simulator);

	/**
	 * If available, return the simulation time of the next observation.
	 */
	public abstract Optional nextObservationPoint();

	public Set getListener() {
		return listeners;
	}

	public boolean hasListener() {
		return !listeners.isEmpty();
	}

}