//ArithSeq.java
//Arithmetic series (sum of arithmetic sequence)
//input first term, common difference, number of terms
//Sn=(n/2)[2a1+(n-1)d]


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


public class ArithSeq extends JApplet {

    JTextField inputFirstField;
    JTextField inputDiffField;
    JTextField inputNumTermsField;
    JTextField outputResultField;
    JLabel errorLabel;
    JTextArea listArea;


    public void init() {
	Container container = getContentPane();
	int panelRowsSize = 3;
	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] );
	}

	Font bigFont = new Font( "Monospaced", Font.BOLD, 16 );
	TextFieldHandler handleTextField = new TextFieldHandler();

	JLabel inputFirstLabel = new JLabel( "1st term" );
	inputFirstLabel.setFont( bigFont );
	panelRows[0].add( inputFirstLabel );

	inputFirstField = new JTextField( 3 );
	inputFirstField.setFont( bigFont );
	panelRows[0].add( inputFirstField );
	inputFirstField.addActionListener( handleTextField );


	JLabel inputDiffLabel = new JLabel( "Difference" );
	inputDiffLabel.setFont( bigFont );
	panelRows[0].add( inputDiffLabel );

	inputDiffField = new JTextField( 3 );
	inputDiffField.setFont( bigFont );
	panelRows[0].add( inputDiffField );
	inputDiffField.addActionListener( handleTextField );


	JLabel inputNumTermsLabel = new JLabel( "# terms" );
	inputNumTermsLabel.setFont( bigFont );
	panelRows[0].add( inputNumTermsLabel );

	inputNumTermsField = new JTextField( 3 );
	inputNumTermsField.setFont( bigFont );
	panelRows[0].add( inputNumTermsField );
	inputNumTermsField.addActionListener( handleTextField );


	outputResultField = new JTextField( 8 );
	outputResultField.setFont( bigFont );
	outputResultField.setEditable( false );
	panelRows[1].add( outputResultField );


	errorLabel = new JLabel( "" );
	errorLabel.setFont( bigFont );
	panelRows[1].add( errorLabel );


	listArea = new JTextArea( 10, 30 );
        Font smallFont = new Font( "Monospaced", Font.BOLD, 12 );
        listArea.setFont( smallFont );
        JScrollPane listScroll = new JScrollPane( listArea );
        panelRows[2].add( listScroll );
                                                                           
    }


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


    private class TextFieldHandler implements ActionListener {
        public void actionPerformed( ActionEvent event ) {

	    errorLabel.setText( "" );

	    int firstTerm=0;
	    try {
		firstTerm = Integer.parseInt( inputFirstField.getText() );
	    }
	    catch (NumberFormatException e) {
		errorLabel.setText( "integer please" );
		return;
	    }

	    int diff=0;
	    try {
		diff = Integer.parseInt( inputDiffField.getText() );
	    }
	    catch (NumberFormatException e) {
		errorLabel.setText( "integer please" );
		return;
	    }

	    int numTerms=0;
	    try {
		numTerms = Integer.parseInt( inputNumTermsField.getText() );
	    }
	    catch (NumberFormatException e) {
		errorLabel.setText( "integer please" );
		return;
	    }
	    if ( numTerms <= 0 ) {
		errorLabel.setText( "positive integer please" );
		return;
	    }

	    outputResultField.setText( "" + (long)((numTerms/2.0)*
				       (2*firstTerm+(numTerms-1)*diff)) );
	    listArea.setText( "" );
		    
	    listArea.append( "i   ai   S\n" );

	    for (int i=0; i<numTerms; i++)
		listArea.append( (i+1) + "  " + (firstTerm+diff*i) + "   " +
				 (long)(((i+1)/2.0)*(2*firstTerm+(i*diff))) + "\n" );
	    
	}
    }

}