/*******************************************************************************
 * Copyright (c) 2009, 2018 Mountainminds GmbH & Co. KG and Contributors
 * 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:
 *    Marc R. Hoffmann - initial API and implementation
 *    
 *******************************************************************************/
package org.jacoco.examples.parser;

import static java.io.StreamTokenizer.TT_EOF;
import static java.io.StreamTokenizer.TT_NUMBER;

import java.io.IOException;
import java.io.StreamTokenizer;
import java.io.StringReader;

import org.jacoco.examples.expressions.Add;
import org.jacoco.examples.expressions.Const;
import org.jacoco.examples.expressions.Div;
import org.jacoco.examples.expressions.IExpression;
import org.jacoco.examples.expressions.Mul;
import org.jacoco.examples.expressions.Sub;

public class ExpressionParser {

	private final StreamTokenizer tokenizer;

	public ExpressionParser(final String s) throws IOException {
		tokenizer = new StreamTokenizer(new StringReader(s));
		tokenizer.ordinaryChar('(');
		tokenizer.ordinaryChar(')');
		tokenizer.ordinaryChar('+');
		tokenizer.ordinaryChar('-');
		tokenizer.ordinaryChar('*');
		tokenizer.ordinaryChar('/');
	}

	public IExpression parse() throws IOException {
		tokenizer.nextToken();
		final IExpression e = term();
		expect(TT_EOF);
		return e;
	}

	private IExpression term() throws IOException {
		IExpression e = product();
		while (true) {
			if (accept('+')) {
				e = new Add(e, product());
			} else if (accept('-')) {
				e = new Sub(e, product());
			} else {
				return e;
			}
		}
	}

	private IExpression product() throws IOException {
		IExpression e = factor();
		while (true) {
			if (accept('*')) {
				e = new Mul(e, factor());
			} else if (accept('/')) {
				e = new Div(e, factor());
			} else {
				return e;
			}
		}
	}

	private IExpression factor() throws IOException {
		final IExpression e;
		if (accept('(')) {
			e = term();
			expect(')');
		} else {
			expect(TT_NUMBER);
			e = new Const(tokenizer.nval);
		}
		return e;
	}

	private boolean accept(final int type) throws IOException {
		if (tokenizer.ttype == type) {
			tokenizer.nextToken();
			return true;
		}
		return false;
	}

	private void expect(final int type) throws IOException {
		if (tokenizer.ttype != type) {
			throw new IOException("Invalid Syntax.");
		}
		tokenizer.nextToken();
	}

}
