/*
 * @(#)ATR.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.*;

/**
 * A Smart Card's answer-to-reset bytes. A Card's ATR object can be obtained
 * by calling {@linkplain Card#getATR}.
 * This class does not attempt to verify that the ATR encodes a semantically
 * valid structure.
 *
 * <p>Instances of this class are immutable. Where data is passed in or out
 * via byte arrays, defensive cloning is performed.
 *
 * @see Card#getATR
 *
 * @version 1.3, 07/20/06
 * @since   1.6
 * @author  Andreas Sterbenz
 * @author  JSR 268 Expert Group
 */
public final class ATR implements java.io.Serializable {

    private static final long serialVersionUID = 6695383790847736493L;

    private byte[] atr;

    private transient int startHistorical, nHistorical;
    
    /**
     * Constructs an ATR from a byte array.
     *
     * @param atr the byte array containing the answer-to-reset bytes
     * @throws NullPointerException if <code>atr</code> is null
     */
    public ATR(byte[] atr) {
        this.atr = atr.clone();
	parse();
    }
    
    private void parse() {
	if (atr.length < 2) {
	    return;
	}
	if ((atr[0] != 0x3b) && (atr[0] != 0x3f)) {
	    return;
	}
	int t0 = (atr[1] & 0xf0) >> 4;
	int n = atr[1] & 0xf;
	int i = 2;
	while ((t0 != 0) && (i < atr.length)) {
	    if ((t0 & 1) != 0) {
		i++;
	    }
	    if ((t0 & 2) != 0) {
		i++;
	    }
	    if ((t0 & 4) != 0) {
		i++;
	    }
	    if ((t0 & 8) != 0) {
		if (i >= atr.length) {
		    return;
		}
		t0 = (atr[i++] & 0xf0) >> 4;
	    } else {
		t0 = 0;
	    }
	}
	int k = i + n;
	if ((k == atr.length) || (k == atr.length - 1)) {
	    startHistorical = i;
	    nHistorical = n;
	}
    }

    /**
     * Returns a copy of the bytes in this ATR.
     *
     * @return a copy of the bytes in this ATR.
     */
    public byte[] getBytes() {
        return atr.clone();
    }
    
    /**
     * Returns a copy of the historical bytes in this ATR.
     * If this ATR does not contain historical bytes, an array of length
     * zero is returned.
     *
     * @return a copy of the historical bytes in this ATR.
     */
    public byte[] getHistoricalBytes() {
	byte[] b = new byte[nHistorical];
	System.arraycopy(atr, startHistorical, b, 0, nHistorical);
	return b;
    }

    /**
     * Returns a string representation of this ATR.
     *
     * @return a String representation of this ATR.
     */
    public String toString() {
	return "ATR: " + atr.length + " bytes";
    }
    
    /**
     * Compares the specified object with this ATR for equality. 
     * Returns true if the given object is also an ATR and its bytes are
     * identical to the bytes in this ATR.
     *
     * @param obj the object to be compared for equality with this ATR
     * @return true if the specified object is equal to this ATR
     */
    public boolean equals(Object obj) {
	if (this == obj) {
	    return true;
	}
	if (obj instanceof ATR == false) {
	    return false;
	}
	ATR other = (ATR)obj;
	return Arrays.equals(this.atr, other.atr);
    }
    
    /**
     * Returns the hash code value for this ATR.
     *
     * @return the hash code value for this ATR.
     */
    public int hashCode() {
	return Arrays.hashCode(atr);
    }

    private void readObject(java.io.ObjectInputStream in)
	    throws java.io.IOException, ClassNotFoundException {
	atr = (byte[])in.readUnshared();
	parse();
    }

}