package au.gov.amsa.ais;
   
   import au.gov.amsa.util.nmea.NmeaMessage;
   import au.gov.amsa.util.nmea.NmeaUtil;
   import au.gov.amsa.util.nmea.Talker;
   
   /**
    * Wraps an NMEA line containing an AIS message with accessor methods.
    * 
   * @author dxm
   * 
   */
  public class AisNmeaMessage {
  
  	private static final AisMessageParser aisParser = new AisMessageParser(
  	        Util.getAisExtractorFactory());
  
  	private final NmeaMessage nmea;
  
  	private final String format;
  
  	private final int fragmentCount;
  
  	private final int fragmentNumber;
  
  	private final String sequentialMessageId;
  
  	private final String channel;
  
  	private final String aisMessage;
  
  	private final int padBits;
  
  	/**
  	 * Constructor.
  	 * 
  	 * @param line
  	 *            is an NMEA line containing an AIS message.
  	 */
  	public AisNmeaMessage(String line) {
  		this(NmeaUtil.parseNmea(validateLine(line)));
  	}
  	
  	public static AisNmeaMessage from(String line) {
  	    return new AisNmeaMessage(line);
  	}
  
  	private static String validateLine(String line) {
  		try {
  			if (!NmeaUtil.isValid(line))
  				throw new AisParseException("invalid checksum: " + line + ", calculated checksum="
  				        + NmeaUtil.getChecksum(line));
  			return line;
  		} catch (RuntimeException e) {
  			throw new AisParseException(e);
  		}
  	}
  
  	public AisNmeaMessage(NmeaMessage nmea) {
  		try {
  			this.nmea = nmea;
  			if (nmea.getItems().size() < 7)
  				throw new AisParseException("ais nmea line must have at least 7 columns:"
  				        + nmea.getItems());
  			format = getItem(0);
  			fragmentCount = Integer.parseInt(getItem(1));
  			fragmentNumber = Integer.parseInt(getItem(2));
  			sequentialMessageId = getItem(3);
  			channel = getItem(4);
  			aisMessage = getItem(5);
  			padBits = Integer.parseInt(nmea.getItems().get(6));
  		} catch (RuntimeException e) {
  			throw new AisParseException(e);
  		}
  	}
  
  	/**
  	 * Returns the tag block unix time value.
  	 * 
  	 * @return
  	 */
  	public Long getTime() {
  		return nmea.getUnixTimeMillis();
  	}
  
  	/**
  	 * Returns the {@link Talker} corresponding to the first two characters of
  	 * the message format type (e.g. AIVDM -> AI).
  	 * 
  	 * @return
  	 */
  	public Talker getTalker() {
  		return nmea.getTalker();
  	}
  
  	/**
  	 * Returns the checksum field at the end of the NMEA line. Does not
  	 * <i>calculate</i> the checksum.
  	 * 
 	 * @param nmea
 	 * @return
 	 */
 	private static String getChecksum(NmeaMessage nmea) {
 		return nmea.getChecksum();
 	}
 
 	/**
 	 * Returns the string at column <code>index</code>, 0 based.
 	 * 
 	 * @param index
 	 * @return
 	 */
 	private String getItem(int index) {
 		return nmea.getItems().get(index);
 	}
 
 	/**
 	 * Returns the NMEA format (from the first column after the tag block if it
 	 * exists).
 	 * 
 	 * @return
 	 */
 	public String getFormat() {
 		return format;
 	}
 
 	/**
 	 * Returns the count of fragments.
 	 * 
 	 * @return
 	 */
 	public int getFragmentCount() {
 		return fragmentCount;
 	}
 
 	/**
 	 * Returns the current fragment number.
 	 * 
 	 * @return
 	 */
 	public int getFragmentNumber() {
 		return fragmentNumber;
 	}
 
 	/**
 	 * Returns the sequential message id.
 	 * 
 	 * @return
 	 */
 	public String getSequentialMessageId() {
 		return sequentialMessageId;
 	}
 
 	/**
 	 * Returns the channel.
 	 * 
 	 * @return
 	 */
 	public String getChannel() {
 		return channel;
 	}
 
 	public int getPadBits() {
 		return padBits;
 	}
 
 	/**
 	 * Returns the parsed contents of column 5 of the AIS NMEA line.
 	 * 
 	 * @return
 	 */
 	public AisMessage getMessage() {
 		AisMessage m = aisParser.parse(aisMessage, nmea.getSource(), padBits);
 		return m;
 	}
 
 	public Timestamped<AisMessage> getTimestampedMessage(long defaultTime) {
 		Long time = getTime();
 		if (time == null)
 			return Timestamped.create(getMessage(), defaultTime);
 		else
 			return Timestamped.create(getMessage(), getTime());
 	}
 
 	public Timestamped<AisMessage> getTimestampedMessage() {
 		Long time = getTime();
 		if (time == null)
 			throw new RuntimeException("nmea did not have timestamp");
 		else
 			return Timestamped.create(getMessage(), getTime());
 	}
 
 	/**
 	 * Returns the checksum (last field in the NMEA line).
 	 * 
 	 * @return
 	 */
 	public String getChecksum() {
 		return nmea.getChecksum();
 	}
 
 	public NmeaMessage getNmea() {
 		return nmea;
 	}
 }