/*
 * Copyright 2009-2010 Yuichiro Moriguchi
 *
 * 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 net.morilib.lisp.graph;

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

import net.morilib.lisp.ConsIterator;
import net.morilib.lisp.Datum;
import net.morilib.lisp.Environment;
import net.morilib.lisp.LispBoolean;
import net.morilib.lisp.LispMessage;
import net.morilib.lisp.MultiValues;
import net.morilib.lisp.Subr;
import net.morilib.lisp.subr.SubrUtils;
import net.morilib.util.Iterators;

/**
 *
 *
 * @author MORIGUCHI, Yuichiro 2011/10/02
 */
public class NextGraphVertex extends Subr {

	/* (non-Javadoc)
	 * @see net.morilib.lisp.Subr#eval(net.morilib.lisp.Datum, net.morilib.lisp.Environment, net.morilib.lisp.LispMessage)
	 */
	@Override
	public Datum eval(Datum body, Environment env, LispMessage mesg) {
		ConsIterator itr = new ConsIterator(body);
		Datum vd = SubrUtils.nextIf(itr, mesg, body);
		Datum lb = Iterators.nextIf(itr);

		SubrUtils.checkTerminated(itr, body, mesg);
		if(vd instanceof ILispVertex) {
			Collection<? extends ILispVertex> cl;
			List<Datum> l = new ArrayList<Datum>();

			cl = ((ILispVertex)vd).getTerminals(lb);
			for(ILispVertex t : cl) {
				l.add((Datum)t);
			}
			return l.isEmpty() ?
					LispBoolean.FALSE : MultiValues.newValues(l);
		} else {
			throw mesg.getError("err.graph.require.vertex", vd);
		}
	}

}
