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SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.

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/*
 * #%L
 * SciJava Common shared library for SciJava software.
 * %%
 * Copyright (C) 2009 - 2016 Board of Regents of the University of
 * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
 * Institute of Molecular Cell Biology and Genetics.
 * %%
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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 * #L%
 */

package org.scijava.app;

import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.scijava.event.EventHandler;
import org.scijava.log.LogService;
import org.scijava.platform.event.AppAboutEvent;
import org.scijava.platform.event.AppPreferencesEvent;
import org.scijava.platform.event.AppQuitEvent;
import org.scijava.plugin.AbstractSingletonService;
import org.scijava.plugin.Parameter;
import org.scijava.plugin.Plugin;
import org.scijava.plugin.PluginService;
import org.scijava.service.Service;

/**
 * Default service for application-level functionality.
 * 
 * @author Curtis Rueden
 */
@Plugin(type = Service.class)
public class DefaultAppService extends AbstractSingletonService implements AppService {

	@Parameter
	private LogService log;

	@Parameter
	private PluginService pluginService;

	/** Read-only table of SciJava applications. */
	private Map apps;

	// -- AppService methods --

	@Override
	public App getApp() {
		final List appList = getInstances();
		if (appList == null || appList.isEmpty()) return null;
		return appList.get(0);
	}

	@Override
	public App getApp(final String name) {
		return apps().get(name);
	}

	@Override
	public Map getApps() {
		return apps();
	}

	// -- SingletonService methods --

	@Override
	public Class getPluginType() {
		return App.class;
	}

	// -- Event handlers --

	@EventHandler(key = "org.scijava.app.AppService#about")
	protected void onEvent(@SuppressWarnings("unused") final AppAboutEvent event)
	{
		getApp().about();
	}

	@EventHandler(key = "org.scijava.app.AppService#prefs")
	protected void onEvent(
		@SuppressWarnings("unused") final AppPreferencesEvent event)
	{
		getApp().prefs();
	}

	@EventHandler(key = "org.scijava.app.AppService#quit")
	protected void onEvent(@SuppressWarnings("unused") final AppQuitEvent event) {
		getApp().quit();
	}

	// -- Helper methods - lazy initialization --

	/** Gets {@link #apps}, initializing if necessary. */
	private Map apps() {
		if (apps == null) initApps();
		return apps;
	}

	/** Initializes {@link #apps}. */
	private synchronized void initApps() {
		if (apps != null) return; // already initialized
		final HashMap map = new HashMap<>();

		for (final App app : getInstances()) {
			final String name = app.getInfo().getName();
			if (!map.containsKey(name)) {
				// no (higher-priority) app with the same name exists
				map.put(name, app);
			}
		}
		apps = Collections.unmodifiableMap(map);
	}

}