// **********************************************************************
//
// Copyright (c) 2001
// ZeroC, Inc.
// Huntsville, AL, USA
//
// All Rights Reserved
//
// **********************************************************************

public class Parser
{
    public Complex.Node
    parse(String buf)
	throws ParseError
    {
	_buf = buf;
	_pos = 0;
	_token = null;

	return start();
    }

    private Complex.Node
    start()
	throws ParseError
    {
	nextToken();
	Complex.Node node = expr();
	if(_token != null)
	{
	    throw new ParseError("Extra garbage: " + _token);
	}
	return node;
    }

    private Complex.Node
    expr()
	throws ParseError
    {
	try
	{
	    if(_token == null)
	    {
		return null;
	    }

	    //
	    // '(' expr ')'
	    //
	    if(_token.charAt(0) == '(')
	    {
		nextToken();

		Complex.Node node = expr();
		if(_token.charAt(0) != ')')
		{
		    throw new ParseError("Expected ')'");
		}

		nextToken();
		return node;
	    }

	    //
	    // expr | expr '+' expr | expr '*' expr
	    //
	    if(!Character.isDigit(_token.charAt(0)))
	    {
		throw new ParseError("Expected number");
	    }
	    
	    Complex.NumberNode number = new Complex.NumberNodeI(Integer.parseInt(_token));
	    Complex.Node result = number;
	    
	    //
	    // expr?
	    //
	    nextToken();
	    if(_token != null)
	    {
		//
		// expr '+' expr
		//
		if(_token.charAt(0) == '+')
		{
		    nextToken();
		    Complex.Node right = expr();
		    result = new Complex.AddNodeI(number, right);
		}
		
		//
		// expr '*' expr
		//
		else if(_token.charAt(0) == '*')
		{
		    nextToken();
		    Complex.Node right = expr();
		    result = new Complex.MultiplyNodeI(number, right);
		}
	    }
	    return result;
	}
	catch(NumberFormatException e)
	{
	    ParseError ex = new ParseError("Error parsing number");
	    ex.initCause(e);
	    throw ex;
	}
    }

    private void
    nextToken()
    {
	//
	// Eat any whitespace.
	//
	while(_pos < _buf.length() && Character.isWhitespace(_buf.charAt(_pos)))
	{
	    _pos++;
	}

	//
	// At the end-of-buffer?
	//
	if(_pos >= _buf.length())
	{
	    _token = null;
	    return;
	}

	StringBuffer buf = new StringBuffer();
	
	//
	// Get the next character
	//
	char c = _buf.charAt(_pos);
	
	//
	// '(', ')', '+' and '*' are tokens.
	//
	if(c == '(' || c == ')' || c == '+' || c == '*')
	{
	    buf.append(c);
	    ++_pos;
	}
	else
	{
	    //
	    // Otherwise it's a number.
	    //
	    while(_pos < _buf.length() && Character.isDigit(_buf.charAt(_pos)))
	    {
		buf.append(_buf.charAt(_pos++));
	    }
	}
	
	_token = buf.toString();
    }

    private String _buf;
    private int _pos;
    private String _token;
}