package au.gov.amsa.ais;
   
   import static java.lang.Integer.parseInt;
   
   import java.util.Calendar;
   import java.util.regex.Pattern;
   
   import au.gov.amsa.util.nmea.NmeaMessage;
   import au.gov.amsa.util.nmea.NmeaMessageParseException;
  import au.gov.amsa.util.nmea.NmeaUtil;
  
  import com.google.common.annotations.VisibleForTesting;
  
  /**
   * Parses a custom ExactEarth NMEA line for AMSA so that we can obtain the
   * actual timestamp of an AIS Position Report (types 1,2,3).
   * 
   * @author dxm
   * 
   */
  public class NmeaMessageExactEarthTimestamp {
  
  	private final NmeaMessage nmea;
  	private final long time;
  	private final String followingSequenceChecksum;
  
  	/**
  	 * Constructor.
  	 * 
  	 * @param line
  	 */
  	public NmeaMessageExactEarthTimestamp(String line) {
  		nmea = NmeaUtil.parseNmea(line);
  		try {
  			Util.checkArgument(isPghp(line), "not an ExactEarth timestamp: "
  					+ line);
  			getFollowingSequenceChecksum();
  			int year = parseInt(getItem(2));
  			int month = parseInt(getItem(3));
  			int day = parseInt(getItem(4));
  			int hour = parseInt(getItem(5));
  			int minute = parseInt(getItem(6));
  			int second = parseInt(getItem(7));
  			int millisecond = parseInt(getItem(8));
  			time = getTime(year, month, day, hour, minute, second, millisecond);
  			followingSequenceChecksum = extractFollowingSequenceChecksum();
  		} catch (RuntimeException e) {
  			throw new AisParseException(e);
  		}
  	}
  
  	private static final Pattern pghpPattern = Pattern
  			.compile("^(\\\\.*\\\\)?\\$PGHP.*$");
  
  	/**
  	 * Returns true if and only if the given NMEA line is a PGHP line. Remember
  	 * that the line can start with a tag block.
  	 * 
  	 * @param line
  	 * @return
  	 */
  	@VisibleForTesting
  	static boolean isPghp(String line) {
  		if (line == null)
  			return false;
  		else
  			// return Pattern.matches("^(\\\\.*\\\\)?\\$PGHP.*$", line);
  			return pghpPattern.matcher(line).matches();
  	}
  
  	/**
  	 * Returns true if the given line is a custom ExactEarth timestamp.
  	 * 
  	 * @param line
  	 * @return
  	 */
  	public static boolean isExactEarthTimestamp(String line) {
  		try {
  			new NmeaMessageExactEarthTimestamp(line);
  			return true;
  		} catch (AisParseException e) {
  			return false;
  		} catch (NmeaMessageParseException e) {
  			return false;
  		}
  	}
  
  	/**
  	 * Returns the item at index, zero based.
  	 * 
  	 * @param index
  	 * @return
  	 */
  	private String getItem(int index) {
  		return nmea.getItems().get(index);
  	}
  
  	/**
  	 * Returns the epoch time in ms.
 	 * 
 	 * @return
 	 */
 	private static long getTime(int year, int month, int day, int hour,
 			int minute, int second, int millisecond) {
 		Calendar cal = Calendar.getInstance(Util.TIME_ZONE_UTC);
 		cal.set(year, month - 1, day, hour, minute, second);
 		cal.set(Calendar.MILLISECOND, millisecond);
 		return cal.getTimeInMillis();
 	}
 
 	/**
 	 * Returns the time in epoch ms.
 	 * 
 	 * @return
 	 */
 	public long getTime() {
 		return time;
 	}
 
 	/**
 	 * Returns the checksum of the message that this timestamp line refers to.
 	 * 
 	 * @return
 	 */
 	public String getFollowingSequenceChecksum() {
 		return followingSequenceChecksum;
 	}
 
 	/**
 	 * Returns the checksum of the message that this timestamp refers to.
 	 * 
 	 * @return
 	 */
 	private String extractFollowingSequenceChecksum() {
 		return getItem(13);
 	}
 }