// BOOTPMedium.java	(C) K. J. Turner	08/03/06

// Boot Protocol medium

package protocol;				// protocol package

import java.util.*;				// utility support
import support.*;				// protocol entity support

/**
  This is the class for an IP medium.

  @author	Iain A. Robin, Kenneth J. Turner
  @version	1.0 (1st September 1999, IAR): initial version <br/>
  <br/>		1.4 (9th March 2006, KJT): updated for JDK 1.5
  <br/>		1.5 (24th July 2010, KJT): minor tidying
*/
public class BOOTPMedium extends Medium {	// protocol medium

  // protocol variables

  private static Vector<Float> randoms;		// random number list
  private static int randomIndex;		// random number index

  public BOOTPMedium() {			// construct medium instance
    super();					// construct as generic medium
    randoms = new Vector<Float>();		// initialise list of randoms
  }

  protected PDU getMatchingPDU(String s) {	// get matching PDU on channel
    PDU pdu;					// PDU
    String sdu;					// PDU contents

    int sourceStart = s.indexOf ('[') + 1;	// get start of entity name
    int sourceEnd = s.indexOf (']');		// get end of entity name
    String sourceName =				// get PDU source
      s.substring(sourceStart, sourceEnd);
    int typeStart = s.indexOf (' ') + 1;	// get start of PDU type
    int typeEnd = s.indexOf ('(');		// get end of PDU type
    String type =				// get PDU type
      s.substring(typeStart, typeEnd);
    int parEnd = s.indexOf (')');		// get end of PDU parameters
    sdu = s.substring(typeEnd + 1, parEnd);	// get PDU parameters
    for (Enumeration e = pdus.elements();	// go through PDUs on channel
	 e.hasMoreElements(); ) {
      pdu = (PDU) e.nextElement();		// get next PDU on channel
      if (pdu != null &&			// valid PDU and ...
	  pdu.type.equals(type) &&		// type matches and ...
	  pdu.getSource().getName(). 		// source matches and ...
	    equals(sourceName) &&
	  sdu.equals(pdu.sdu))			// SDU matches
	return((pdu));				// return with this PDU
    }
    return((null));				// return no PDU as no match
  }

  public void initialise() {			// initialise medium
    super.initialise();				// initialise generic medium
    randomIndex = 0;				// initialise randoms index
  }

  protected static float random() {		// random number (from list)
    Float rand;					// random number

    if (randomIndex < randoms.size())		// get number from list?
      rand = (Float) randoms.elementAt(randomIndex++); // get number from list
    else {					// make new random number
      rand = new Float(Math.random());		// get random number
      randoms.addElement(rand);			// add to list
      randomIndex++;				// increment list index
    }
    return((rand.floatValue()));		// return random number
  }

}