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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 - 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.
 * %%
 * 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
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package org.scijava.event;

import java.util.ArrayList;
import java.util.Set;

import org.scijava.plugin.Parameter;
import org.scijava.plugin.Plugin;
import org.scijava.service.AbstractService;
import org.scijava.service.Service;

/**
 * Default service for keeping a history of SciJava events.
 * 
 * @author Curtis Rueden
 */
@Plugin(type = Service.class)
public class DefaultEventHistory extends AbstractService implements
	EventHistory
{

	@Parameter
	private EventService eventService;

	/** Event details that have been recorded. */
	private ArrayList history = new ArrayList<>();

	private ArrayList listeners =
		new ArrayList<>();

	private boolean active;

	// -- EventHistory methods --

	@Override
	public void setActive(final boolean active) {
		this.active = active;
	}

	@Override
	public boolean isActive() {
		return active;
	}

	@Override
	public void clear() {
		history.clear();
	}

	@Override
	public String toHTML(final Set> filtered,
		final Set> highlighted)
	{
		final StringBuilder sb = new StringBuilder();
		for (final EventDetails details : history) {
			final Class eventType = details.getEventType();
			if (filtered != null && filtered.contains(eventType)) {
				// skip filtered event type
				continue;
			}
			final boolean bold =
				highlighted != null && highlighted.contains(eventType);
			sb.append(details.toHTML(bold));
		}
		return sb.toString();
	}

	@Override
	public void addListener(final EventHistoryListener l) {
		synchronized (listeners) {
			listeners.add(l);
		}
		// someone is listening; start recording
		setActive(true);
	}

	@Override
	public void removeListener(final EventHistoryListener l) {
		synchronized (listeners) {
			listeners.remove(l);
		}
		if (listeners.isEmpty()) {
			// if no one is listening, stop recording
			setActive(false);
		}
	}

	// -- Event handlers --

	@EventHandler
	protected void onEvent(final SciJavaEvent event) {
		if (!active) return; // only record events while active
		final EventDetails details = new EventDetails(event);
		history.add(details);
		notifyListeners(details);
	}

	// -- Helper methods --

	private void notifyListeners(final EventDetails details) {
		synchronized (listeners) {
			for (final EventHistoryListener l : listeners) {
				l.eventOccurred(details);
			}
		}
	}

}