/*
 * @(#)ResponseAPDU.java	1.3 06/07/20
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.smartcardio;

import java.util.Arrays;

/**
 * A response APDU as defined in ISO/IEC 7816-4. It consists of a conditional
 * body and a two byte trailer.
 * This class does not attempt to verify that the APDU encodes a semantically
 * valid response.
 *
 * <p>Instances of this class are immutable. Where data is passed in or out
 * via byte arrays, defensive cloning is performed.
 *
 * @see CommandAPDU
 * @see CardChannel#transmit CardChannel.transmit
 *
 * @version 1.3, 07/20/06
 * @since   1.6
 * @author  Andreas Sterbenz
 * @author  JSR 268 Expert Group
 */
public final class ResponseAPDU implements java.io.Serializable {

    private static final long serialVersionUID = 6962744978375594225L;

    /** @serial */
    private byte[] apdu;

    /**
     * Constructs a ResponseAPDU from a byte array containing the complete
     * APDU contents (conditional body and trailed).
     *
     * <p>Note that the byte array is cloned to protect against subsequent
     * modification.
     *
     * @param apdu the complete response APDU
     *
     * @throws NullPointerException if apdu is null
     * @throws IllegalArgumentException if apdu.length is less than 2
     */
    public ResponseAPDU(byte[] apdu) {
	apdu = apdu.clone();
	check(apdu);
	this.apdu = apdu;
    }
    
    private static void check(byte[] apdu) {
	if (apdu.length < 2) {
	    throw new IllegalArgumentException("apdu must be at least 2 bytes long");
	}
    }

    /**
     * Returns the number of data bytes in the response body (Nr) or 0 if this 
     * APDU has no body. This call is equivalent to
     * <code>getData().length</code>.
     *
     * @return the number of data bytes in the response body or 0 if this APDU
     * has no body.
     */
    public int getNr() {
	return apdu.length - 2;
    }

    /**
     * Returns a copy of the data bytes in the response body. If this APDU as
     * no body, this method returns a byte array with a length of zero.
     *
     * @return a copy of the data bytes in the response body or the empty
     *    byte array if this APDU has no body.
     */
    public byte[] getData() {
	byte[] data = new byte[apdu.length - 2];
	System.arraycopy(apdu, 0, data, 0, data.length);
	return data;
    }

    /**
     * Returns the value of the status byte SW1 as a value between 0 and 255.
     *
     * @return the value of the status byte SW1 as a value between 0 and 255.
     */
    public int getSW1() {
	return apdu[apdu.length - 2] & 0xff;
    }

    /**
     * Returns the value of the status byte SW2 as a value between 0 and 255.
     *
     * @return the value of the status byte SW2 as a value between 0 and 255.
     */
    public int getSW2() {
	return apdu[apdu.length - 1] & 0xff;
    }

    /**
     * Returns the value of the status bytes SW1 and SW2 as a single
     * status word SW.
     * It is defined as
     * <code>(getSW1() << 8) | getSW2()</code>.
     *
     * @return the value of the status word SW.
     */
    public int getSW() {
	return (getSW1() << 8) | getSW2();
    }

    /**
     * Returns a copy of the bytes in this APDU.
     *
     * @return a copy of the bytes in this APDU.
     */
    public byte[] getBytes() {
        return apdu.clone();
    }

    /**
     * Returns a string representation of this response APDU.
     *
     * @return a String representation of this response APDU.
     */
    public String toString() {
	return "ResponseAPDU: " + apdu.length + " bytes, SW="
	    + Integer.toHexString(getSW());
    }
    
    /**
     * Compares the specified object with this response APDU for equality. 
     * Returns true if the given object is also a ResponseAPDU and its bytes are
     * identical to the bytes in this ResponseAPDU.
     *
     * @param obj the object to be compared for equality with this response APDU
     * @return true if the specified object is equal to this response APDU
     */
    public boolean equals(Object obj) {
	if (this == obj) {
	    return true;
	}
	if (obj instanceof ResponseAPDU == false) {
	    return false;
	}
	ResponseAPDU other = (ResponseAPDU)obj;
	return Arrays.equals(this.apdu, other.apdu);
    }
    
    /**
     * Returns the hash code value for this response APDU.
     *
     * @return the hash code value for this response APDU.
     */
    public int hashCode() {
	return Arrays.hashCode(apdu);
    }
    
    private void readObject(java.io.ObjectInputStream in)
	    throws java.io.IOException, ClassNotFoundException {
	apdu = (byte[])in.readUnshared();
	check(apdu);
    }

}