/*******************************************************************************
 * Copyright (c) 2007, 2010 Association for Decentralized Information Management
 * in Industry THTH ry.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     VTT Technical Research Centre of Finland - initial API and implementation
 *******************************************************************************/
package org.simantics.db.layer0.genericrelation.combinators;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

import org.simantics.db.ReadGraph;
import org.simantics.db.exception.DatabaseException;
import org.simantics.db.layer0.adapter.GenericRelation;
import org.simantics.db.layer0.genericrelation.AbstractRelation;
import org.simantics.utils.datastructures.Pair;

/**
 * Takes the intersection of multiple relations.
 */
public class Intersection extends AbstractRelation {

	GenericRelation realizable = null;
	Collection<GenericRelation> constraints;
	
	public Intersection(Collection<GenericRelation> relations) {
		for(GenericRelation relation : relations)
			if(realizable == null && relation.isRealizable()) {
				realizable = relation;
			}
			else
				constraints.add(relation);
	}
	
	public Intersection(GenericRelation realizable, Collection<GenericRelation> constraints) {
		assert(realizable.isRealizable());
		this.realizable = realizable;
		this.constraints = constraints;
	}

	@Override
	public boolean contains(ReadGraph g, Object[] tuple) throws DatabaseException {
		if(!realizable.contains(g, tuple))
			return false;
		for(GenericRelation relation : constraints)
			if(!relation.contains(g, tuple))
				return false;
		return true;
	}

	@Override
	public boolean isRealizable() {
		return realizable != null;
	}

	@Override
	public List<Object[]> realize(ReadGraph g) throws DatabaseException {
		ArrayList<Object[]> result = new ArrayList<Object[]>();
		loop:
		for(Object[] tuple : realizable.realize(g)) {
			for(GenericRelation constraint : constraints)
				if(!constraint.contains(g, tuple))
					continue loop;
			result.add(tuple);
		}
		return result;
	}	

	// TODO optimize select
	
	@Override
	public GenericRelation selectByRelation(String bindingPattern,
			GenericRelation constraint) {
		if(realizable != null)
			return new Intersection(realizable.selectByRelation(bindingPattern, constraint),
					constraints);
		else
			return super.selectByRelation(bindingPattern, constraint);
	}
	
	@Override
	public Pair<String, String>[] getFields() {
		if(realizable != null)
			return realizable.getFields();
		for(GenericRelation relation : constraints)
			return relation.getFields();
		return null;
	}

}