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A generic query algebra for RDF queries.
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/*******************************************************************************
 * Copyright (c) 2015 Eclipse RDF4J contributors, Aduna, and others.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Distribution License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 *******************************************************************************/
package org.eclipse.rdf4j.query.algebra;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * A "multi-projection" that can produce multiple solutions from a single set of bindings.
 */
public class MultiProjection extends UnaryTupleOperator {

	/*-----------*
	 * Variables *
	 *-----------*/

	/**
	 * The lists of projections.
	 */
	private List projections = new ArrayList<>();

	/*--------------*
	 * Constructors *
	 *--------------*/

	public MultiProjection() {
	}

	public MultiProjection(TupleExpr arg) {
		super(arg);
	}

	public MultiProjection(TupleExpr arg, Iterable projections) {
		this(arg);
		addProjections(projections);
	}

	/*---------*
	 * Methods *
	 *---------*/

	public List getProjections() {
		return Collections.unmodifiableList(projections);
	}

	public void setProjections(Iterable projections) {
		this.projections.clear();
		addProjections(projections);
	}

	public void addProjections(Iterable projections) {
		for (ProjectionElemList projection : projections) {
			addProjection(projection);
		}
	}

	public void addProjection(ProjectionElemList projection) {
		assert projection != null : "projection must not be null";
		projections.add(projection);
		projection.setParentNode(this);
	}

	@Override
	public Set getBindingNames() {
		Set bindingNames = new HashSet<>();

		for (ProjectionElemList projElemList : projections) {
			bindingNames.addAll(projElemList.getProjectedNames());
		}

		return bindingNames;
	}

	@Override
	public Set getAssuredBindingNames() {
		Set bindingNames = new HashSet<>();

		if (projections.size() >= 1) {
			Set assuredSourceNames = getArg().getAssuredBindingNames();

			bindingNames.addAll(projections.get(0).getProjectedNamesFor(assuredSourceNames));

			for (int i = 1; i < projections.size(); i++) {
				bindingNames.retainAll(projections.get(i).getProjectedNamesFor(assuredSourceNames));
			}
		}

		return bindingNames;
	}

	@Override
	public  void visit(QueryModelVisitor visitor) throws X {
		visitor.meet(this);
	}

	@Override
	public  void visitChildren(QueryModelVisitor visitor) throws X {
		for (ProjectionElemList projElemList : projections) {
			projElemList.visit(visitor);
		}

		super.visitChildren(visitor);
	}

	@Override
	public void replaceChildNode(QueryModelNode current, QueryModelNode replacement) {
		if (replaceNodeInList(projections, current, replacement)) {
			return;
		}
		super.replaceChildNode(current, replacement);
	}

	@Override
	public boolean equals(Object other) {
		if (other instanceof MultiProjection && super.equals(other)) {
			MultiProjection o = (MultiProjection) other;
			return projections.equals(o.getProjections());
		}
		return false;
	}

	@Override
	public int hashCode() {
		return super.hashCode() ^ projections.hashCode();
	}

	@Override
	public MultiProjection clone() {
		MultiProjection clone = (MultiProjection) super.clone();

		clone.projections = new ArrayList<>(getProjections().size());
		for (ProjectionElemList pe : getProjections()) {
			clone.addProjection(pe.clone());
		}

		return clone;
	}

}