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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.AISMessage24PartB;
import nl.esi.metis.aisparser.Sixbit;
import nl.esi.metis.aisparser.UtilsDimensions30;
import nl.esi.metis.aisparser.UtilsShipType8;
import nl.esi.metis.aisparser.UtilsSpare;
import nl.esi.metis.aisparser.UtilsString;
import nl.esi.metis.aisparser.annotations.AISIllegalValueAnnotation;
import nl.esi.metis.aisparser.provenance.VDMMessageProvenance;
import cern.colt.bitvector.BitVector;

/* ESI AIS Parser
 * 
 * Copyright 2011/2012 by Pierre van de Laar (Embedded Systems Institute)
 * Copyright 2008 by Brian C. Lane 
 * All Rights Reserved
 * 
 */

/** This class implements AIS messages of type 24 Part B.
 *  * Field Nr     Field Name                          NrOf Bits   (from, to )
 * ------------------------------------------------------------------------
 *  1           messageID                                  6    (   1,   6)
 *  2           repeatIndicator                            2    (   7,   8)
 *  3           userID                                    30    (   9,  38)
 *  4           partNumber                                 2    (  39,  40)
 *  5           typeOfShipAndCargoType                     8    (  41,  48)
 *  6           vendorID                                  42    (  49,  90)
 *  7           callSign                                  42    (  91, 132)
 *  8           dimensionOrMotherID                       30    ( 133, 162)
 *  9           spare                                      6    ( 163, 168)
 *                                                      ---- +
 *                           (maximum) number of bits    168
 * 
 * @author Pierre van de Laar
 * @author Pierre America
 * @author Brian C. Lane
 */
class AISMessage24PartBImpl extends AISMessage24Impl implements AISMessage24PartB {

	/** The length of a valid message of type 24 Part B. */
	public static final int LENGTHPartB = 168;

	/** Checks whether the content is a valid message of type 24 Part B. (length & Part number)
	 * @param content possible message type 24 B
	 * @return true if this could be a valid message of type 24 Part B
	 */
	public static boolean valid(Sixbit content)
	{
		return ( (content.length() == LENGTHPartB) && (content.getIntFromTo(PARTNUMBER_FROM,PARTNUMBER_TO) == 1) );
	}
	
	public static boolean isTypeB(Sixbit content)
	{
		return AISMessage24Impl.valid(content) && (content.getIntFromTo(PARTNUMBER_FROM,PARTNUMBER_TO) == 1);
	}
	
	/**
	 * Return the difference in available and needed bits to parse this sixbit as an AisMessagePositionReport
	 * A positive difference indicates that there are more bits available than needed by the standard.
	 * @param sb
	 * @return
	 */
	public static int differenceInBits(Sixbit sb)
	{	
		return (sb.available() - LENGTHPartB);
	}

	/** The number of the first bit of the ship type field */ 
	private static final int TYPEOFSHIPANDCARGOTYPE_FROM = 41;

	/** The number of the last bit of the ship type field */ 
	private static final int TYPEOFSHIPANDCARGOTYPE_TO = 48;

	/** The ship and cargo type */
	private int typeOfShipAndCargoType;

	/** Returns the type of ship and cargo type.
	 * @return an integer value representing the type of ship and cargo type (8 bits)
	 */
	public int getTypeOfShipAndCargoType() { return typeOfShipAndCargoType; }

	/** The number of the first bit of the vendor ID field */ 
	private static final int VENDORID_FROM = 49;

	/** The number of the last bit of the vendor ID field */ 
	private static final int VENDORID_TO = 90;

	/** The vendor ID */
	private BitVector vendorID;

	/** Returns the vendor ID.
	 * @return a BitVector object representing the vendor ID (42 bits)
	 */
	public BitVector getVendorID() { return vendorID; }

	/** The number of the first bit of the call sign field */ 
	private static final int CALLSIGN_FROM = 91;

	/** The number of the last bit of the call sign field */ 
	private static final int CALLSIGN_TO = 132;

	/** The call sign */
	private String callSign;
	
	/** Returns the call sign.
	 * @return a string representing the call sign (42 bits)
	 */
	public String getCallSign() { return callSign; }

	/** The number of the first bit of the dimensions or mother ID field */ 
	private static final int DIMENSIONORMOTHERID_FROM = 133;

	/** The number of the last bit of the dimensions or mother ID field */ 
	private static final int DIMENSIONORMOTHERID_TO = 162;

	/** The dimension or mother ID */
	private BitVector dimensionOrMotherID;

	/** Returns the dimensions or mother ID.
	 * @return a BitVector object representing the dimensions or mother ID (30 bits)
	 */
	public BitVector getDimensionOrMotherID() { return dimensionOrMotherID; }

	/** The number of the first spare bit */ 
	private static final int SPARE_FROM = 163;

	/** The number of the last spare bit */ 
	private static final int SPARE_TO = 168;

	/** The value of the spare bits */
	private int spare;

	/** Returns the spare bits.
	 * @return the integer value of the spare bits.
	 */
	public int getSpare() { return spare; }
	
	/** Returns the part number.
	 * @return the part number. This is always 1 for a Part B message.
	 */
	@Override
	public int getPartNumber() {
		return 1;
	}

	/** Constructs an AIS message 24 Part B object.
	 * @param content the content of the AIS message
	 * @param prov the provenance of the message
	 * @precondition valid(content)
	 */
	public AISMessage24PartBImpl(Sixbit content, VDMMessageProvenance prov)
	{		
		super(content, prov);
		assert(valid(content));
		typeOfShipAndCargoType = content.getIntFromTo(TYPEOFSHIPANDCARGOTYPE_FROM,TYPEOFSHIPANDCARGOTYPE_TO);
		vendorID = content.getBitVectorFromTo(VENDORID_FROM,VENDORID_TO);
		callSign = UtilsString.stripAtSigns(content.getStringFromTo(CALLSIGN_FROM,CALLSIGN_TO));
		dimensionOrMotherID = content.getBitVectorFromTo(DIMENSIONORMOTHERID_FROM,DIMENSIONORMOTHERID_TO);
		spare = content.getIntFromTo(SPARE_FROM,SPARE_TO);
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare", spare, 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 + "B" 
								+ SEPARATOR + UtilsShipType8.shipTypeToString(getTypeOfShipAndCargoType())
								+ SEPARATOR + getVendorID()
								+ SEPARATOR + getCallSign()
								+ SEPARATOR + UtilsDimensions30.toString(getDimensionOrMotherID());		//Is this the best way to print? 
	}
}