/*
 * 
 * Package:  com.silentmission.ewallet.cardapplets
 * Filename: TestWallet.java
 * Class:    TestWallet
 * Date:     Mar 10, 2005 10:02:46 AM
 *
 */
package com.silentmission.ewallet.cardapplets.testwallet;


import javacard.framework.*;

/**
 *
 * Class TestWallet
 *
 */
public class TestWallet extends javacard.framework.Applet{

 // boilerplate code to install applet with JCRE:
  public static void install(byte[] b, short off, byte len) {
    // OP-compliant JavaCard applet registration:
    new TestWallet().register(b, (short)(off+1), b[off]);
  }

  /* constants declaration */

  // code of CLA byte in the command APDU header
  final static byte Wallet_CLA =(byte)0xB0;

  // codes of INS byte in the command APDU header
  final static byte CREDIT = (byte) 0x30;
  final static byte DEBIT = (byte) 0x40;
  final static byte GET_BALANCE = (byte) 0x50;

  // maximum balance
  final static short MAX_BALANCE = 0x7FFF;
  // maximum transaction amount
  final static byte MAX_TRANSACTION_AMOUNT = 127;

  // signal invalid transaction amount
  // amount > MAX_TRANSACTION_AMOUNT or amount < 0
  final static short SW_INVALID_TRANSACTION_AMOUNT = 0x6A83;

  // signal that the balance exceed the maximum
  final static short SW_EXCEED_MAXIMUM_BALANCE = 0x6A84;
  // signal the the balance becomes negative
  final static short SW_NEGATIVE_BALANCE = 0x6A85;

  /* instance variables declaration */
  short balance;

  //private TestWallet (byte[] bArray,short bOffset,byte bLength){
  private TestWallet () {

  } 


  public boolean select() {

    return true;
  }

  public void deselect() {
   
  }

  public void process(APDU apdu) {

    // APDU object carries a byte array (buffer) to
    // transfer incoming and outgoing APDU header
    // and data bytes between card and CAD

    // At this point, only the first header bytes
    // [CLA, INS, P1, P2, P3] are available in
    // the APDU buffer.
    // The interface javacard.framework.ISO7816
    // declares constants to denote the offset of
    // these bytes in the APDU buffer

    byte[] buffer = apdu.getBuffer();

    // check SELECT APDU command
    if ((buffer[ISO7816.OFFSET_CLA] == 0) &&
       (buffer[ISO7816.OFFSET_INS] == (byte)(0xA4)) )
      return;

    // verify the reset of commands have the
    // correct CLA byte, which specifies the
    // command structure
    if (buffer[ISO7816.OFFSET_CLA] != Wallet_CLA)
       ISOException.throwIt (ISO7816.SW_CLA_NOT_SUPPORTED);

    switch (buffer[ISO7816.OFFSET_INS]) {
      case GET_BALANCE:   getBalance(apdu);
                          return;
      case DEBIT:         debit(apdu);
                          return;
      case CREDIT:        credit(apdu);
                          return;
     
      default:       	  ISOException.throwIt(ISO7816.SW_INS_NOT_SUPPORTED);
      					  System.out.println("poo poo");
    }

 }   // end of process method


 /* Method to add funds to eWallet */
 private void credit(APDU apdu) {

    byte[] buffer = apdu.getBuffer();

    // Lc byte denotes the number of bytes in the
    // data field of the command APDU
    byte numBytes = buffer[ISO7816.OFFSET_LC];


    // indicate that this APDU has incoming data
    // and receive data starting from the offset
    // ISO7816.OFFSET_CDATA following the 5 header
    // bytes.
    byte byteRead =
              (byte)(apdu.setIncomingAndReceive());

    // it is an error if the number of data bytes
    // read does not match the number in Lc byte
    if ( ( numBytes != 1 ) || (byteRead != 1) )
     ISOException.throwIt(ISO7816.SW_WRONG_LENGTH);

    // get credit amount
    byte creditAmount =
                  buffer[ISO7816.OFFSET_CDATA];

    // check credit amount
    if ( ( creditAmount > MAX_TRANSACTION_AMOUNT)
         || ( creditAmount < 0 ) )
        ISOException.throwIt
                   (SW_INVALID_TRANSACTION_AMOUNT);

    // check the new balance
    if ( (short)( balance + creditAmount)  > MAX_BALANCE )
       ISOException.throwIt
                     (SW_EXCEED_MAXIMUM_BALANCE);

    // credit the amount to eWallet cash
    balance = (short)(balance + creditAmount);
  } 

  /* Deducts amount from eWallet  */
  private void debit(APDU apdu) {

    byte[] buffer = apdu.getBuffer();

    byte numBytes =
            (byte)(buffer[ISO7816.OFFSET_LC]);

    byte byteRead =
            (byte)(apdu.setIncomingAndReceive());

    if ( ( numBytes != 1 ) || (byteRead != 1) )
       ISOException.throwIt
                        (ISO7816.SW_WRONG_LENGTH);

    // get debit amount
    byte debitAmount =
                     buffer[ISO7816.OFFSET_CDATA];

    // check debit amount
    if ( ( debitAmount > MAX_TRANSACTION_AMOUNT)
         ||  ( debitAmount < 0 ) )
       ISOException.throwIt
                   (SW_INVALID_TRANSACTION_AMOUNT);

    // check the new balance
    if ( (short)( balance - debitAmount ) < (short)0 )
         ISOException.throwIt(SW_NEGATIVE_BALANCE);

    balance = (short) (balance - debitAmount);
  } 

 
  private void getBalance(APDU apdu) {

    byte[] buffer = apdu.getBuffer();

    // inform system that the applet has finished
    // processing the command and the system should
    // now prepare to construct a response APDU
    // which contains data field
    short le = apdu.setOutgoing();

    if ( le < 2 )
       ISOException.throwIt
                       (ISO7816.SW_WRONG_LENGTH);

    //informs the CAD the actual number of bytes
    //returned
    apdu.setOutgoingLength((byte)2);

    // move the balance data into the APDU buffer
    // starting at the offset 0
    buffer[0] = (byte)(balance >> 8);
    buffer[1] = (byte)(balance & 0xFF);

    // send the 2-byte balance at the offset
    // 0 in the apdu buffer
    apdu.sendBytes((short)0, (short)2);

  } 
}