/* ***********************************************************
 * Smart Cards: Toward a Modern Run-time Platform
 * ETH Zurich, WS 2005/2006
 * 
 * Exercise 3b - Solution
 *************************************************************/

package exercise3b;

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

public class Exercise3b extends Applet implements MultiSelectable {

	private final short[] mod_since_select;

	private final short[] mod_since_reset;

	private final short[] history;

	private short mod_since_install;

	public Exercise3b() {
		mod_since_select = JCSystem.makeTransientShortArray((short) 1,
				JCSystem.CLEAR_ON_DESELECT);
		mod_since_reset = JCSystem.makeTransientShortArray((short) 1,
				JCSystem.CLEAR_ON_RESET);
		mod_since_install = 0;
		history = new short[4];
	}

	public static void install(byte[] bArray, short bOffset, byte bLength) {
		new Exercise3b().register(bArray, (short) (bOffset + 1),
				bArray[bOffset]);
	}

	public boolean select(boolean appInstStillActive) {
		return true;
	}

	public void deselect(boolean appInstStillActive) {

	}

	public void process(APDU apdu) {
		if (selectingApplet()) {
			return;
		}

		byte[] buf = apdu.getBuffer();

		if (JCSystem.getAssignedChannel() == 0) {
			short value = history[mod_since_install & 0x03];
			switch (buf[ISO7816.OFFSET_INS]) {
			case (byte) 0x00: // add p1 to value
				value += buf[ISO7816.OFFSET_P1];
				break;
			case (byte) 0x02: // subtract p2 to value
				value -= buf[ISO7816.OFFSET_P2];
				break;
			case (byte) 0x04: // set value to p1 * p2
				value = (short) (buf[ISO7816.OFFSET_P1] * buf[ISO7816.OFFSET_P2]);
				break;
			default:
				ISOException.throwIt(ISO7816.SW_INS_NOT_SUPPORTED);
			}
			if (value != history[mod_since_install & 0x03]) {
				JCSystem.beginTransaction();
				mod_since_select[0]++;
				mod_since_reset[0]++;
				mod_since_install++;
				history[mod_since_install & 0x03] = value;
				JCSystem.commitTransaction();
			}
		} else {
			switch (buf[ISO7816.OFFSET_INS]) {
			case (byte) 0x00:
				Util
						.setShort(buf, (short) 0,
								history[mod_since_install & 0x03]);
				break;
			case (byte) 0x02:
				Util.setShort(buf, (short) 0, mod_since_select[0]);
				break;
			case (byte) 0x04:
				Util.setShort(buf, (short) 0, mod_since_reset[0]);
				break;
			case (byte) 0x06:
				Util.setShort(buf, (short) 0, mod_since_install);
				break;
			case (byte) 0x08:
				if (mod_since_install < 3) {
					ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
				} else {
					Util.setShort(buf, (short) 0,
							history[(mod_since_install - 3) & 0x03]);
				}
				break;
			default:
				ISOException.throwIt(ISO7816.SW_INS_NOT_SUPPORTED);
			}
			apdu.setOutgoingAndSend((short) 0, (short) 2);
		}
	}
}