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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.AISMessage15;
import nl.esi.metis.aisparser.AISMessage15Unit;
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 15
 * Interrogation
 * 
 * Field Nr     Field Name                          NrOf Bits   (from, to )
 * ------------------------------------------------------------------------
 *  1	messageID                               	   6	(   1,   6)
 *  2	repeatIndicator                         	   2	(   7,   8)
 *  3	userID                                  	  30	(   9,  38)
 *  4	spare1                                  	   2	(  39,  40)
 *  5	destinationID1                          	  30	(  41,  70)
 *  6	messageID1_1                            	   6	(  71,  76)
 *  7	slotOffset1_1                           	  12	(  77,  88)
 *  8	spare2                                  	   2	(  89,  90)
 *  9	messageID1_2                            	   6	(  91,  96)
 * 10	slotOffset1_2                           	  12	(  97, 108)
 * 11	spare3                                  	   2	( 109, 110)
 * 12	destinationID2                          	  30	( 111, 140)
 * 13	messageID2_1                            	   6	( 141, 146)
 * 14	slotOffset2_1                           	  12	( 147, 158)
 * 15	spare4                                  	   2	( 159, 160)
 *                                                      ---- +
 *                           (maximum) number of bits    160
 */
class AISMessage15Impl extends AISMessageImpl implements AISMessage15 {
	public static final int LENGTH_ONEDESTINATION_ONEMESSAGE = 88;
	public static final int LENGTH_ONEDESTINATION_TWOMESSAGES = 112;	//TODO: check with practice: do length of 108 and 110 also exist?
	public static final int LENGTH_TWODESTINATIONS = 160;
	
	public static boolean validLength(int length)
	{
		return (length == LENGTH_ONEDESTINATION_ONEMESSAGE) ||
		       (length == LENGTH_ONEDESTINATION_TWOMESSAGES) ||
		       (length == LENGTH_TWODESTINATIONS) ;
	}
	
	/**
	 * 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 >= LENGTH_TWODESTINATIONS)
		{
			return available - LENGTH_TWODESTINATIONS;
		}
		else if (available >= LENGTH_ONEDESTINATION_TWOMESSAGES)
		{
			return available - LENGTH_ONEDESTINATION_TWOMESSAGES;
		}
		else
		{
			return available - LENGTH_ONEDESTINATION_ONEMESSAGE;
		}
	}


	private static final int SPARE1_FROM = 39;
	private static final int SPARE1_TO = 40;

	private int spare1;
	/** spare1
	 * @return int value of spare1 (2 bits [39,40])
	 */
	public int getSpare1() { return spare1; }

	private static final int INTERROGATION1_FROM = 41;

	private static final int SPARE2_FROM = 89;
	private static final int SPARE2_TO = 90;

	private int spare2 = 0;    //default value is zero
	/** spare2
	 * @return int value of spare2 (2 bits [89,90])
	 */
	public int getSpare2() { return spare2; }


	private static final int SPARE3_FROM = 109;
	private static final int SPARE3_TO = 110;

	private int spare3 = 0;      //default value is zero
	/** spare3
	 * @return int value of spare3 (2 bits [109,110] {or 4?} )
	 */
	public int getSpare3() { return spare3; }

	private static final int INTERROGATION2_FROM = 111;

	private static final int SPARE4_FROM = 159;
	private static final int SPARE4_TO = 160;

	private int spare4 = 0;		//default value is zero 
	/** spare4
	 * @return int value of spare4 (2 bits [159,160])
	 */
	public int getSpare4() { return spare4; }

	private AISMessage15Unit[] interrogations;
	/** interrogations
	 * @return AISMessage15Unit[] value of interrogations
	 */
	public AISMessage15Unit[] getInterrogations() { return interrogations; }

	/** AISMessage 15 constructor
	 * @param content AIS content
	 * @param prov the provenance of the message
	 * @precondition validLength(content.length()) && AISMessageBase.getMessageId(content)==15
	 */
	public AISMessage15Impl(Sixbit content, VDMMessageProvenance prov)
	{
		super(content, prov);
		assert(validLength(content.length()));
		assert(getMessageID() == 15);

		spare1 = content.getIntFromTo(SPARE1_FROM,SPARE1_TO);
		
		if (content.length() == LENGTH_ONEDESTINATION_ONEMESSAGE)
		{
			interrogations = new AISMessage15Unit[1];
			interrogations[0] = new AISMessage15UnitImpl(INTERROGATION1_FROM, 1, content);
		}
		else if (content.length() == LENGTH_ONEDESTINATION_TWOMESSAGES)
		{
			interrogations = new AISMessage15Unit[1];
			interrogations[0] = new AISMessage15UnitImpl(INTERROGATION1_FROM, 2, content);
			spare2 = content.getIntFromTo(SPARE2_FROM,SPARE2_TO);
			spare3 = content.getIntFromTo(SPARE3_FROM,content.length());		// four bits instead of two to get to byte boundary at bit position 112 !
		}
		else 
		{
			assert (content.length() == LENGTH_TWODESTINATIONS);
			
			interrogations = new AISMessage15Unit[2];
			interrogations[0] = new AISMessage15UnitImpl(INTERROGATION1_FROM, 2, content);
			interrogations[1] = new AISMessage15UnitImpl(INTERROGATION2_FROM, 1, content);
			spare2 = content.getIntFromTo(SPARE2_FROM,SPARE2_TO);
			spare3 = content.getIntFromTo(SPARE3_FROM,SPARE3_TO);
			spare4 = content.getIntFromTo(SPARE4_FROM,SPARE4_TO);
		}
		
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare1))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare1", spare1, UtilsSpare.range));
	    }
		
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare2)) //default value is zero, so only annotation when really parsed 
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare2", spare2, UtilsSpare.range));
	    }
	    
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare3)) //default value is zero, so only annotation when really parsed 
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare3", spare3, UtilsSpare.range));
	    }
	    
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare4)) //default value is zero, so only annotation when really parsed 
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpar4e", spare4, UtilsSpare.range));
	    }
	}
}