package au.gov.amsa.ais;
   
   import com.google.common.annotations.VisibleForTesting;
   
   /**
    * Provides the fields inside the Communications portion of an AIS Message.
    * 
    * @author dxm
    * 
   */
  public class Communications {
  
  	private final int startIndex;
  	private final int syncState;
  	private final int slotTimeout;
  	private final Integer receivedStations;
  	private final Integer slotNumber;
  	private final Integer hourUtc;
  	private final Integer minuteUtc;
  	private final Integer slotOffset;
  
  	/**
  	 * Constructor.
  	 * 
  	 * @param extractor
  	 * @param startIndex
  	 */
  	public Communications(AisExtractor extractor, int startIndex) {
  		this.startIndex = startIndex;
  		syncState = extractor.getValue(startIndex, startIndex + 2);
  		slotTimeout = extractor.getValue(startIndex + 2, startIndex + 5);
  		receivedStations = getReceivedStations(extractor, slotTimeout,
  				startIndex);
  		slotNumber = getSlotNumber(extractor, slotTimeout, startIndex);
  		hourUtc = getHourUtc(extractor, slotTimeout, startIndex);
  		minuteUtc = getMinuteUtc(extractor, slotTimeout, startIndex);
  		slotOffset = getSlotOffset(extractor, slotTimeout, startIndex);
  	}
  
  	/**
  	 * Returns received stations as per 1371-4.pdf.
  	 * 
  	 * @param extractor
  	 * @param slotTimeout
  	 * @param startIndex
  	 * @return
  	 */
  	@VisibleForTesting
  	static Integer getReceivedStations(AisExtractor extractor, int slotTimeout,
  			int startIndex) {
  		if (slotTimeout == 3 || slotTimeout == 5 || slotTimeout == 7)
  			return extractor.getValue(startIndex + 5, startIndex + 19);
  		else
  			return null;
  	}
  
  	/**
  	 * Returns slot number as per 1371-4.pdf.
  	 * 
  	 * @param extractor
  	 * @param slotTimeout
  	 * @param startIndex
  	 * @return
  	 */
  	@VisibleForTesting
  	static Integer getSlotNumber(AisExtractor extractor, int slotTimeout,
  			int startIndex) {
  		if (slotTimeout == 2 || slotTimeout == 4 || slotTimeout == 6)
  			return extractor.getValue(startIndex + 5, startIndex + 19);
  		else
  			return null;
  	}
  
  	/**
  	 * Returns hour UTC as per 1371-4.pdf.
  	 * 
  	 * @param extractor
  	 * @param slotTimeout
  	 * @param startIndex
  	 * @return
  	 */
  	private static Integer getHourUtc(AisExtractor extractor, int slotTimeout,
  			int startIndex) {
  		if (slotTimeout == 1) {
  			// skip the msb bit
  			int hours = extractor.getValue(startIndex + 5, startIndex + 10);
  			return hours;
  		} else
  			return null;
  	}
  
  	/**
  	 * Returns minute UTC as per 1371-4.pdf.
  	 * 
  	 * @param extractor
  	 * @param slotTimeout
  	 * @param startIndex
  	 * @return
  	 */
 	private static Integer getMinuteUtc(AisExtractor extractor,
 			int slotTimeout, int startIndex) {
 		if (slotTimeout == 1) {
 			// skip the msb bit
 			int minutes = extractor.getValue(startIndex + 10, startIndex + 17);
 			return minutes;
 		} else
 			return null;
 	}
 
 	/**
 	 * Returns slot offset as per 1371-4.pdf.
 	 * 
 	 * @param extractor
 	 * @param slotTimeout
 	 * @param startIndex
 	 * @return
 	 */
 	private static Integer getSlotOffset(AisExtractor extractor,
 			int slotTimeout, int startIndex) {
 		if (slotTimeout == 0)
 			return extractor.getValue(startIndex + 5, startIndex + 19);
 		else
 			return null;
 	}
 
 	/**
 	 * Returns sync state as per 1371-4.pdf.
 	 * 
 	 * @return
 	 */
 	public int getSyncState() {
 		return syncState;
 	}
 
 	/**
 	 * Returns slot timeout as per 1371-4.pdf.
 	 * 
 	 * @return
 	 */
 	public int getSlotTimeout() {
 		return slotTimeout;
 	}
 
 	/**
 	 * Returns received stations as per 1371-4.pdf.
 	 * 
 	 * @return
 	 */
 	public Integer getReceivedStations() {
 		return receivedStations;
 	}
 
 	/**
 	 * Returns slot number as per 1371-4.pdf.
 	 * 
 	 * @return
 	 */
 	public Integer getSlotNumber() {
 		return slotNumber;
 	}
 
 	/**
 	 * Returns hour UTC as per 1371-4.pdf.
 	 * 
 	 * @return
 	 */
 	public Integer getHourUtc() {
 		return hourUtc;
 	}
 
 	/**
 	 * Returns minute UTC as per 1371-4.pdf.
 	 * 
 	 * @return
 	 */
 	public Integer getMinuteUtc() {
 		return minuteUtc;
 	}
 
 	/**
 	 * Returns total minutes (60* hour + minute) in UTC.
 	 * 
 	 * @return
 	 */
 	public Integer getMinutesUtc() {
 		return getMinutesUtc(slotTimeout, hourUtc, minuteUtc);
 	}
 
 	/**
 	 * Returns minutes UTC (60* hour + minute) in UTC if slot timeout is 1, null
 	 * otherwise.
 	 * 
 	 * @param slotTimeout
 	 * @param hour
 	 * @param minute
 	 * @return
 	 */
 	private static Integer getMinutesUtc(int slotTimeout, Integer hour,
 			Integer minute) {
 		if (slotTimeout == 1) {
 			return hour * 60 + minute;
 		} else
 			return null;
 	}
 
 	/**
 	 * Returns slot offset as per 1371-4.pdf.
 	 * 
 	 * @return
 	 */
 	public Integer getSlotOffset() {
 		return slotOffset;
 	}
 
 	@Override
 	public String toString() {
 		StringBuilder builder = new StringBuilder();
 		builder.append("Communications [startIndex=");
 		builder.append(startIndex);
 		builder.append(", syncState=");
 		builder.append(syncState);
 		builder.append(", slotTimeout=");
 		builder.append(slotTimeout);
 		builder.append(", receivedStations=");
 		builder.append(receivedStations);
 		builder.append(", slotNumber=");
 		builder.append(slotNumber);
 		builder.append(", hourUtc=");
 		builder.append(hourUtc);
 		builder.append(", minuteUtc=");
 		builder.append(minuteUtc);
 		builder.append(", slotOffset=");
 		builder.append(slotOffset);
 		builder.append("]");
 		return builder.toString();
 	}
 
 }