//converted from C++ to Java applet.  DFW

//modified for boolean expressions  DFW
// & | ~ operators, variables, 0 1

//Stroustrup's real-number calculator.  C++ Programming Language chapter 6.

//Ex.  to evaluate with p true and q false:
// p=1; q=0; (p&(~(~p|q)))|(p&q)
//or as:
// 1&(~(~1|0))|(1&0)
//as command line argument or interactively.

//Interactively: either on one line, or each semicoloned statement on own line:
//p=1
//q=0;
//(p&(~(~p|q)))|(p&q)
//semicolon is optional.

//White space optional:   (p & (~( ~p|q))) |(p & q)

//Parens optional.  & higher precedence than |
//p&(~(~p|q))|p&q


import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;

public class ParserLogic extends JApplet {

    public final char  NAME='\000',      
	NUMBER='\001',
	END='\002',
	OR='|',    
	NEGATE='~', 
	AND='&',  
	PRINT=';', 
	ASSIGN='=', 
	LP='(',    
	RP=')';

    char curr_tok = PRINT;
    String input;
    int index;

    boolean bool_value;
    String string_value;
    int no_of_errors;
    Map table;

    JTextField inputField;
    JLabel resultLabel;
    JButton clearButton;
    JLabel errorLabel;

    public void init() {
	table = new HashMap();

	Container container = getContentPane();
	int panelRowsSize = 4;
	container.setLayout( new GridLayout( panelRowsSize, 1 ) );

	JPanel [] panelRows = new JPanel[panelRowsSize];
	for (int i=0; i<panelRowsSize; i++) {
	    panelRows[i] = new JPanel();
	    panelRows[i].setLayout( new FlowLayout() );
	    container.add( panelRows[i] );
	}

	JLabel inputLabel = new JLabel( "Enter boolean expression" );
	panelRows[0].add( inputLabel );

	inputField = new JTextField( 20 );
	panelRows[0].add( inputField );
	inputField.addActionListener( 
        	new ActionListener () {
		    public void actionPerformed( ActionEvent event ) {
			
			table.clear();
			errorLabel.setText( "" );
			resultLabel.setText( "" );
			input = inputField.getText();			
			index = 0;
			while ( index < input.length() ) {
			    get_token();
			    if (curr_tok == END)
				break;
			    if (curr_tok == PRINT)
				continue;
			    resultLabel.setText( "Result= " + expr( false ) );
			}
		    }
		}
	);

	resultLabel = new JLabel( "Result=" );
	panelRows[1].add( resultLabel );


	clearButton = new JButton( "Clear" );
	panelRows[2].add( clearButton );
	clearButton.addActionListener( 
        	new ActionListener () {
		    public void actionPerformed( ActionEvent event ) {
			inputField.setText( "" );
			resultLabel.setText( "Result=" );
			errorLabel.setText( "" );
			inputField.requestFocusInWindow();
		    }
		}
		);

	errorLabel = new JLabel( "" );
	panelRows[3].add( errorLabel );
    }


    public void start() {
	inputField.requestFocusInWindow();
    }


    boolean expr (boolean get) {
	boolean left=term(get);
	for (;;)
	    switch(curr_tok) {
	    case OR:
		left |= term(true);
		break;

	    default:
		return left;
	    }
    }


    boolean term (boolean get) {
	boolean left=prim(get);
	for (;;)
	    switch (curr_tok) {
	    case AND:
		left &= prim(true);
		break;

	    default:
		return left;
	    }
    }


    boolean prim (boolean get) {
	if (get) 
	    get_token();

	switch (curr_tok) {
	case NUMBER:
	    {boolean v = bool_value;
	    get_token();
	    return v;
	    }
	case NAME:                //needs work...
	    {if (get_token() == ASSIGN) {
		boolean v = expr(true);
		table.put( string_value, new Boolean( v ) );
		return v;
	    }
	    else
		if ( table.containsKey( string_value ) )
		    return ((Boolean)table.get(string_value)).booleanValue();
		else
		    return error( "undefined variable" );
	    }
	case NEGATE:
	    return !prim(true);
	case LP:
	    {boolean e = expr(true);
	    if (curr_tok != RP)
		return error("')' expected");
	    get_token();
	    return e;
	    }
	default:
	    return error("primary expected");
	}
    }


    //Token_value get_token() {
    char get_token() {
	char ch;
	do {
	    if ( index == input.length() )
		return curr_tok=END;
	    else 
		ch = input.charAt( index++ );
	} while (ch!='\n' && ch==' ');

	switch (ch) {
	case ';':
	case '\n':
	    return curr_tok=PRINT;
	case '&':
	case '|':
	case '~':
	case '(':
	case ')':
	case '=':
	    return curr_tok = ch;
	case '0':
	case 'f':
	case 'F':
	    bool_value = false;
	    return curr_tok=NUMBER;
	case '1':
	case 't':
	case 'T':
	    bool_value = true;
	    return curr_tok=NUMBER;
	default:
	    if ( Character.isLetter( ch ) ) {
		string_value = ""+ch;
		while (index<input.length() && 
		       Character.isLetter( input.charAt(index )))

		    string_value += input.charAt( index++ );
		return curr_tok=NAME;
	    }
	    error("bad token");
	    return curr_tok=PRINT;
	}
    }
    


    boolean error( String s ) {
	errorLabel.setText( "Error: " + s );
	resultLabel.setText( "Result=" );
	return true;
    }


}