/*
 * Vorlesung "Vernetzte Systeme" WS 1999/2000, Prof. Dr. F. Mattern
 * ----------------------------------------------------------------
 * Packet.java:
 * Encapsulates packets into a simple one-line String (no newlines).
 *
 */

public class Packet {
    private static char DELIMITER = ',';

    /* see "man ascii" for ASCII table */
    private static char EOL = 10;       /* Protect Newline "\n" (0x0A) */
    private static char EOL_QUOTED = 7; /* by replacing it with BEL (0x07) */
    
    private int id;
    private String data;

    /* Constructor: create new (empty) packet */
    public Packet () {
        this.id = -1;
	this.data = null;
    }

    /* Constructor: create new packet from id and data 
     * (packager takes care of size)
     */
    public Packet (int id, String data) {
        this.id = id;
	this.data = data;
    }

    /* Constructor: initialize new packet (parse) from inputLine */
    public Packet (String inputLine) {
        int data_idx = inputLine.indexOf(DELIMITER);
        this.id = Integer.valueOf(
                      inputLine.substring(0,data_idx)).intValue();
        this.data = unquote(inputLine.substring(data_idx+1));
    }

    /* re-initialize (empty) packet with data, bound by packetsize */
    public String fill (int id, String data, int packetSize) {
        this.id = id;
	this.data = data.substring(0,packetSize-1);
	/* returns left-over data that did not fit */
	return data.substring(packetSize);
    }

    /* return packet id */
    public int id() {
        return this.id;
    }
    
    /* return packet data */
    public String data() {
        return this.data;
    }
    
    /* return one-line string representation of both ID and data */
    public String asString() {
        return (formatACK(id) + String.valueOf(DELIMITER) + quote(data));
    }

    public static String formatACK (int id) {
        /* uugh! ugly as sin. but hey, who cares!? */
        return ((id < 10000 ? "0" : "") +
                (id <  1000 ? "0" : "") +
                (id <   100 ? "0" : "") +
                (id <    10 ? "0" : "") + id);
    }

    /* returns quoted (i.e. newlines are substituted) representation 
     * of data to send over string 
     */
    private String quote (String data) {
	return data.replace(EOL, EOL_QUOTED);
    }
    
    /* replaces substitution characters with newlines */
    private String unquote (String data) {
	return data.replace(EOL_QUOTED, EOL);
    }
}