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Lunar Base is a simple game framework written in Java. It is written using an entity-component-system architecture.
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/*
 * This file is part of the lunar-base package.
 *
 * Copyright (c) 2014 Eric Fritz
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
 * and associated documentation files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or
 * substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
 * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

package com.kauridev.lunarbase;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

/**
 * A manager that handles a collection of systems.
 *
 * @author Eric Fritz
 */
public class GameSystemManager
{
	/**
	 * Whether the manager has been initialized.
	 */
	private boolean isInitialized = false;

	/**
	 * A map of systems by layer.
	 */
	private Map> systems = new TreeMap<>();

	/**
	 * Adds a system to the list. If the manager has already been initialized, this system will be
	 * initialized immediately.
	 *
	 * @param system The system.
	 * @param layer  The order this system should be processed in relation to other systems.
	 */
	public void addSystem(GameSystem system, int layer) {
		if (isInitialized) {
			system.init();
		}

		if (!systems.containsKey(layer)) {
			systems.put(layer, new ArrayList());
		}

		systems.get(layer).add(system);
	}

	/**
	 * Initializes all the systems.
	 */
	public void init() {
		for (List s : systems.values()) {
			for (GameSystem system : s) {
				system.init();
			}
		}

		isInitialized = true;
	}

	/**
	 * Calls {@link GameSystem#exit()} on all the systems.
	 */
	public void exit() {
		for (List s : systems.values()) {
			for (GameSystem system : s) {
				system.exit();
			}
		}

		systems.clear();
	}

	/**
	 * Called when it has been determined that game logic needs to be processed.
	 * 
	 * All systems will be processed in relation to their relative order (lower layers are processed
	 * first). Systems at the same layer will be processed in the order they were added to the
	 * manager.
	 *
	 * @param elapsed The number of milliseconds elapsed since the last call to process.
	 */
	public void process(double elapsed) {
		for (List s : systems.values()) {
			for (GameSystem system : s) {
				system.process(elapsed);
			}
		}
	}
}