/*
 * #%L
 * SciJava Common shared library for SciJava software.
 * %%
 * Copyright (C) 2009 - 2017 Board of Regents of the University of
 * Wisconsin-Madison, Broad Institute of MIT and Harvard, Max Planck
 * Institute of Molecular Cell Biology and Genetics, University of
 * Konstanz, and KNIME GmbH.
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 *    this list of conditions and the following disclaimer.
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package org.scijava.plugin;

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

import org.scijava.log.LogService;
import org.scijava.object.ObjectService;

/**
 * Abstract base class for {@link SingletonService}s.
 * 
 * @author Curtis Rueden
 * @param <PT> Plugin type of the {@link SingletonPlugin}s being managed.
 */
public abstract class AbstractSingletonService<PT extends SingletonPlugin>
	extends AbstractPTService<PT> implements SingletonService<PT>
{

	@Parameter
	private LogService log;

	@Parameter
	private ObjectService objectService;

	// TODO: Listen for PluginsAddedEvent and PluginsRemovedEvent
	// and update the list of singletons accordingly.

	/** List of singleton plugin instances. */
	private List<PT> instances;

	private Map<Class<? extends PT>, PT> instanceMap;

	// -- SingletonService methods --

	@Override
	public ObjectService objectService() {
		return objectService;
	}

	@Override
	public List<PT> getInstances() {
		if (instances == null) initInstances();
		return instances;
	}

	@SuppressWarnings("unchecked")
	@Override
	public <P extends PT> P getInstance(final Class<P> pluginClass) {
		if (instanceMap == null) initInstances();
		return (P) instanceMap.get(pluginClass);
	}

	// -- Helper methods --

	private synchronized void initInstances() {
		if (instances != null) return;

		final List<PT> list = Collections.unmodifiableList(filterInstances(
			pluginService().createInstancesOfType(getPluginType())));

		final HashMap<Class<? extends PT>, PT> map =
			new HashMap<>();

		for (final PT plugin : list) {
			@SuppressWarnings("unchecked")
			final Class<? extends PT> ptClass =
				(Class<? extends PT>) plugin.getClass();
			map.put(ptClass, plugin);
		}

		log.debug("Found " + list.size() + " " + getPluginType().getSimpleName() +
			" plugins.");

		instanceMap = map;
		instances = list;
	}

}
