Walker.java

/*
 * Copyright (C) 2013 lichtflut Forschungs- und Entwicklungsgesellschaft mbH
 *
 * 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.arastreju.sge.traverse;

import org.arastreju.sge.SNOPS;
import org.arastreju.sge.model.ResourceID;
import org.arastreju.sge.model.nodes.SemanticNode;

import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/**
 * <p>
 *  A Walker is a utility for walking through a graph.
 * </p>
 *
 * <p>
 * 	Created Feb 6, 2012
 * </p>
 *
 * @author Oliver Tigges
 */
public class Walker {

	private Set<SemanticNode> nodes = new HashSet<SemanticNode>();

	// ----------------------------------------------------

	protected Walker(final SemanticNode... nodes) {
		for (SemanticNode current : nodes) {
			this.nodes.add(current);
		}
	}

	protected Walker(final Collection<? extends SemanticNode> nodes) {
		this.nodes.addAll(nodes);
	}

	// ----------------------------------------------------

	public static Walker start(final SemanticNode... startNodes) {
		return new Walker(startNodes);
	}

	public static Walker start(final Collection<? extends SemanticNode> startNodes) {
		return new Walker(startNodes);
	}

	// ----------------------------------------------------

	public Walker walk(final ResourceID predicate) {
		Set<SemanticNode> result = new HashSet<SemanticNode>();
		for (SemanticNode current : nodes) {
			result.addAll(getObjects(current, predicate));
		}
		this.nodes = result;
		return this;
	}

	// ----------------------------------------------------

	public Iterator<SemanticNode> iterator() {
		return nodes.iterator();
	}

	public int size() {
		return nodes.size();
	}

	public boolean isEmpty() {
		return nodes.isEmpty();
	}

	public boolean isSingle() {
		return nodes.size() == 1;
	}

	public SemanticNode getSingle() {
		if (nodes.isEmpty()) {
			return null;
		} else {
			return nodes.iterator().next();
		}
	}

	// ----------------------------------------------------

	public boolean matches(final String value) {
		return matches(ValueMatcher.equals(value));
	}

	public boolean matches(final ResourceID rid) {
		return matches(ResourceMatcher.equals(rid));
	}

	public boolean matches(final Matcher matcher) {
		return matcher.matches(nodes);
	}

	// ----------------------------------------------------

	@Override
	public int hashCode() {
		return nodes.hashCode();
	}

	@Override
	public boolean equals(final Object o) {
		return nodes.equals(o);
	}

	@Override
	public String toString() {
		return "Walker{" + nodes + '}';
	}

	// ----------------------------------------------------

	private Collection<SemanticNode> getObjects(final SemanticNode src, final ResourceID predicate) {
		if (src == null || !src.isResourceNode()) {
			return Collections.emptySet();
		} else {
			return SNOPS.objects(src.asResource(), predicate);
		}
	}

}