/* ***********************************************************
 * Smart Cards: Toward a Modern Run-time Platform
 * ETH Zurich, WS 2005/2006
 * 
 * Exercise 1 - Solution
 *************************************************************/

package exercise1;

import javacard.framework.APDU;
import javacard.framework.Applet;
import javacard.framework.ISO7816;
import javacard.framework.ISOException;
import javacard.framework.Util;

public class Calculator extends Applet {
	public static void install(byte[] bArray, short bOffset, byte bLength) {
		// GP-compliant JavaCard applet registration
		new Calculator().register(bArray, (short) (bOffset + 1),
				bArray[bOffset]);
	}

	private static final byte[] CALC = { (byte) 'c', (byte) 'a', (byte) 'l',
			(byte) 'c', (byte) 'u', (byte) 'l', (byte) 'a', (byte) 't',
			(byte) 'o', (byte) 'r' };

	public void process(APDU apdu) {
		// Good practice: Return 9000 on SELECT
		if (selectingApplet()) {
			return;
		}

		byte[] buf = apdu.getBuffer();
		switch (buf[ISO7816.OFFSET_INS]) {
		case (byte) 0x00:
			apdu.setOutgoingAndSend((short) 0, Util.arrayCopy(CALC, (short) 0,
					buf, (short) 0, (short) CALC.length));
			return; // return here so we won't try to send again
		case (byte) 0x02:
			buf[0] = (byte) (buf[ISO7816.OFFSET_P1] + buf[ISO7816.OFFSET_P2]);
			break;
		case (byte) 0x04:
			buf[0] = (byte) (buf[ISO7816.OFFSET_P1] - buf[ISO7816.OFFSET_P2]);
			break;
		case (byte) 0x06:
			buf[0] = (byte) (buf[ISO7816.OFFSET_P1] * buf[ISO7816.OFFSET_P2]);
			break;
		case (byte) 0x08:
			if (buf[ISO7816.OFFSET_P2] == 0) {
				ISOException.throwIt(ISO7816.SW_INCORRECT_P1P2);
			}
			buf[0] = (byte) (buf[ISO7816.OFFSET_P1] / buf[ISO7816.OFFSET_P2]);
			break;
		case (byte) 0x0a:
			short n = (short) (ISO7816.OFFSET_CDATA + apdu
					.setIncomingAndReceive());
			byte sum = 0;
			while (n-- > ISO7816.OFFSET_CDATA) {
				sum += buf[n];
			}
			buf[0] = sum;
			break;
		default:
			ISOException.throwIt(ISO7816.SW_INS_NOT_SUPPORTED);
		}
		apdu.setOutgoingAndSend((short) 0, (short) 1);
	}
}