/* GNU Prolog for Java
 * Copyright (C) 1997-1999  Constantine Plotnikov
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 3 of the License, or (at your option) any later version.
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA  02111-1307, USA. The text of license can be also found
 * at http://www.gnu.org/copyleft/lgpl.html
 */
package gnu.prolog.vm.buildins.io;

import gnu.prolog.io.PrologStream;
import gnu.prolog.term.IntegerTerm;
import gnu.prolog.term.Term;
import gnu.prolog.term.VariableTerm;
import gnu.prolog.vm.ExecuteOnlyCode;
import gnu.prolog.vm.Interpreter;
import gnu.prolog.vm.PrologException;
import gnu.prolog.vm.TermConstants;

/**
 * prolog code
 */
public class Predicate_peek_byte extends ExecuteOnlyCode
{
	@Override
	public int execute(Interpreter interpreter, boolean backtrackMode, gnu.prolog.term.Term args[])
			throws PrologException
	{
		PrologStream stream = interpreter.getEnvironment().resolveStream(args[0]);
		Term in_byte = args[1];
		int b = 0;
		if (in_byte instanceof VariableTerm)
		{
		}
		else if (in_byte instanceof IntegerTerm)
		{
			IntegerTerm ch = (IntegerTerm) in_byte;
			b = ch.value;
			if (b < -1 || 255 < b)
			{
				PrologException.typeError(TermConstants.inByteAtom, in_byte);
			}
		}
		else
		{
			PrologException.typeError(TermConstants.inByteAtom, in_byte);
		}
		Term rc = IntegerTerm.get(stream.peekByte(args[0], interpreter));
		return interpreter.unify(in_byte, rc);
	}
}
