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This package supports the parsing of AIS messages in Java. AIS, the Automatic Identification System, is a system aiming at improving maritime safety by exchanging messages between ships, other vehicles in particular aircraft involved in search-and-rescue (SAR), and (fixed) base stations. To be precise, this package support the ITU-R M.1371-4 AIS standard. See our extensive javadoc and in particular the class AISParser for more information on how to use this package. The parser was used in the Poseidon project, and is improved in the Metis project to better handle uncertain information. Both projects were led by the Embedded Systems Institute. In both projects Thales Nederlands was the carrying industrial partner, and multiple Dutch universities participated.

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package nl.esi.metis.aisparser.impl;

import nl.esi.metis.aisparser.AISMessage12;
import nl.esi.metis.aisparser.Sixbit;
import nl.esi.metis.aisparser.UtilsSpare;
/** ESI AIS Parser
 * 
 * Copyright 2011/2012 by Pierre van de Laar (Embedded Systems Institute)
 * Copyright 2008 by Brian C. Lane 
 * All Rights Reserved
 * 
 * @author Pierre van de Laar
 * @author Brian C. Lane
 */
import nl.esi.metis.aisparser.annotations.AISIllegalValueAnnotation;
import nl.esi.metis.aisparser.provenance.VDMMessageProvenance;


/** AIS Message 12
 * Addressed Safety Related Message
 *
 * Field Nr     Field Name                          NrOf Bits   (from, to )
 * ------------------------------------------------------------------------
 *  1	messageID                               	   6	(   1,   6)
 *  2	repeatIndicator                         	   2	(   7,   8)
 *  3	userID                                  	  30	(   9,  38)
 *  4	sequenceNumber                          	   2	(  39,  40)
 *  5	destinationID                           	  30	(  41,  70)
 *  6	retransmitFlag                          	   1	(  71,  71)
 *  7	spare                                   	   1	(  72,  72)
 *  8	safetyRelatedText                       	 936	(  73,1008)
 *                                                      ---- +
 *                           (maximum) number of bits   1008
 */
class AISMessage12Impl extends AISMessageImpl implements AISMessage12 {
	public static final int MINLENGTH = 72;
	public static final int MAXLENGTH = 1008;
	
	public static boolean validLength(int length)
	{
		return (MINLENGTH <= length && length <= MAXLENGTH);
	}

	/**
	 * Return the difference in available and needed bits to parse this sixbit as an AISMessage
	 * A positive difference indicates that there are more bits available than needed by the standard.
	 * @param sb
	 * @return
	 */
	public static int differenceInBits(Sixbit sb)
	{
		final int available = sb.available();
		if (available > MAXLENGTH)
		{
			return (available - MAXLENGTH);
		}
		else if (available < MINLENGTH)
		{
			return available - MINLENGTH;
		}
		else
		{
			return 0;
		}
	}

	private static final int SEQUENCENUMBER_FROM = 39;
	private static final int SEQUENCENUMBER_TO = 40;

	private int sequenceNumber;
	/** sequenceNumber
	 * @return int value of sequenceNumber (2 bits [39,40])
	 */
	public int getSequenceNumber() { return sequenceNumber; }


	private static final int DESTINATIONID_FROM = 41;
	private static final int DESTINATIONID_TO = 70;

	private int destinationID;
	/** destinationID
	 * @return int value of destinationID (30 bits [41,70])
	 */
	public int getDestinationID() { return destinationID; }


	private static final int RETRANSMITFLAG_BITINDEX = 71;

	private boolean retransmitFlag;
	/** retransmitFlag
	 * @return boolean value of retransmitFlag (bit 71)
	 */
	public boolean getRetransmitFlag() { return retransmitFlag; }


	private static final int SPARE1_FROM = 72;
	private static final int SPARE1_TO = 72;

	private int spare1;
	/** spare1
	 * @return int value of spare1 (1 bits [72,72])
	 */
	public int getSpare1() { return spare1; }

	private int spare2;
	/** spare2
	 * @return int value of spare2 (at end to adhere to byte boundaries)
	 */
	public int getSpare2() { return spare2; }

	
	private static final int SAFETYRELATEDTEXT_FROM = 73;
	
	private String safetyRelatedText;
	/** safetyRelatedText
	 * @return String value of safetyRelatedText (936 bits [73,1008])
	 */
	public String getSafetyRelatedText() { return safetyRelatedText; }

	/** AISMessage 12 constructor
	 * @param content AIS content
	 * @param prov the provenance of the message
	 * @precondition validLength(content.length()) && AISMessageBase.getMessageId(content)==12
	 */
	public AISMessage12Impl(Sixbit content, VDMMessageProvenance prov)
	{
		super(content, prov);
		assert(validLength(content.length()));
		assert(getMessageID() == 12);
	       
	    sequenceNumber = content.getIntFromTo(SEQUENCENUMBER_FROM,SEQUENCENUMBER_TO);
	    destinationID = content.getIntFromTo(DESTINATIONID_FROM,DESTINATIONID_TO);
	    retransmitFlag = content.getBoolean(RETRANSMITFLAG_BITINDEX);
	    spare1 = content.getIntFromTo(SPARE1_FROM,SPARE1_TO);
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare1))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare1", spare1, UtilsSpare.range));
	    }
	    int nrofSpare = (content.length()-SAFETYRELATEDTEXT_FROM+1)%Sixbit.BITSNEEDEDFORCHAR;
	    safetyRelatedText = content.getStringFromTo(SAFETYRELATEDTEXT_FROM,content.length()-nrofSpare);
	    spare2 = content.getIntFromTo(content.length()-nrofSpare,content.length());
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare2))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare2", spare2, UtilsSpare.range));
	    }
	}
	

	/** Generates a String representing the AIS message. 
	 * Format: all fields are shown in the order as specified by the standard separated by the SEPARATOR string.
	 */
	@Override
	public String toString() {
		return super.toString() + SEPARATOR + Integer.toString(getSequenceNumber()) 
								+ SEPARATOR + Integer.toString(getDestinationID()) 
								+ SEPARATOR + (retransmitFlag ? "retransmitted" : "no retransmission") 
								+ SEPARATOR + getSafetyRelatedText();
	}
}