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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 java.util.ArrayList;
import java.util.List;

import nl.esi.metis.aisparser.AISMessage;
import nl.esi.metis.aisparser.Sixbit;
import nl.esi.metis.aisparser.annotations.Annotation;
import nl.esi.metis.aisparser.provenance.AISMessageProvenance;
import nl.esi.metis.aisparser.provenance.VDMMessageProvenance;

/** This is the base class implementation for all AIS messages. It implements the fields that they all have in common.
 * 
 *  * Field Nr     Field Name                          NrOf Bits   (from,  to)
 * ------------------------------------------------------------------------
 *    1         messageID                                   6   (   1,   6)
 *    2         repeatIndicator                             2   (   7,   8)
 *    3         userID                                     10   (   9,  38)
 * 
 * 
 * @author Pierre van de Laar
 * @author Pierre America
 */

class AISMessageImpl implements AISMessage {
	
	/** This string is used by this class and its subclasses to separate the different fields in generated strings. */
	public static final String SEPARATOR = "|";			//bug prevention: using a string detects a nasty bug (two +'s) which is accepted by a char (but yielding unexpected results)

	/** Extracts the message ID from the content of an AIS message.
	 * @param content the content of an AIS message
	 * @return integer value of the message ID (6 bits [1,6])
	 */
	public static int getMessageID(Sixbit content)
	{
		return content.getIntFromTo(MESSAGEID_FROM,MESSAGEID_TO);
	}
	
	/** Changes the message ID from the content of an AIS message.
	 * @param content the content of an AIS message
	 */
	public static void setMessageID(Sixbit content, int id)
	{
		content.setIntFromTo(id, MESSAGEID_FROM,MESSAGEID_TO);
	}

	/** The position of the first bit of the message ID. */
	private static final int MESSAGEID_FROM = 1;
	
	/** The position of the last bit of the message ID. */
	private static final int MESSAGEID_TO = 6;

	/** The message ID. */
	private int messageID;

	/** Returns the message ID.
	 * @return integer value of message ID (6 bits [1,6])
	 */
	public int getMessageID() { return messageID; }

	/** The position of the first bit of the repeat indicator. */
	private static final int REPEATINDICATOR_FROM = 7;

	/** The position of the last bit of the repeat indicator. */
	private static final int REPEATINDICATOR_TO = 8;

	/** The repeat indicator */
	private int repeatIndicator;

	/** Returns the repeat indicator.
	 * @return integer value of repeat indicator (2 bits [7,8])
	 */
	public int getRepeatIndicator() { return repeatIndicator; }

	/** The position of the first bit of the user ID. */
	private static final int USERID_FROM = 9;

	/** The position of the last bit of the user ID. */
	private static final int USERID_TO = 38;

	/** The user ID. */
	private int userID;
	
	/** Returns the user ID.
	 * @return integer value of user ID (30 bits [9,38])
	 */
	public int getUserID() { return userID; }
	
	/** The provenance */
	private VDMMessageProvenance provenance;
	
	/** The annotations */
	protected List annotations = new ArrayList();
	
	/**
	 * Add annotation a to annotations of this AISMessage
	 * @param a
	 */
	public void AddAnnotation (Annotation a)
	{
		annotations.add(a);
	}
	
	/** Returns the provenance, i.e., a description of where the AIS message came from, including a time stamp.
	 * @return the provenance
	 */
	public AISMessageProvenance getProvenance() {
		return new AISMessageProvenance(provenance, annotations);
	}
	
	
	/** Constructor, used by subclasses to initialize the fields of this class.
	 * @param content the content of an AIS message
	 * @param provenance the provenance of the AIS message
	 */
    protected AISMessageImpl(Sixbit content, VDMMessageProvenance provenance)
	{
    	messageID = content.getIntFromTo(MESSAGEID_FROM,MESSAGEID_TO);
    	repeatIndicator = content.getIntFromTo(REPEATINDICATOR_FROM,REPEATINDICATOR_TO);
    	userID = content.getIntFromTo(USERID_FROM,USERID_TO);
    	this.provenance = provenance;
	}
    
    /** Generates a String representing the parsed AISMessage.
     * Format:
     * all fields are shown in the order and units as specified by the standard separated by the SEPARATOR string.
     * @see java.lang.Object#toString()
     */
    public String toString()
    {
    	return  Integer.toString(messageID) + SEPARATOR +
    			Integer.toString(repeatIndicator) + SEPARATOR +
    			Integer.toString(userID);
    }
}