content: package tim.prune.function.olc;
  
  class ParseException extends Exception {}
  
  /**
   * Pair of coordinates
   */
  class CoordPair
  {
  	/** Alphabet of allowed characters */
  	private static final String ALPHABET = "23456789CFGHJMPQRVWX";
  
  	public final double lat;
  	public final double lon;
  
  	/** Constructor */
  	public CoordPair(double inLat, double inLon)
  	{
  		lat = inLat;
  		lon = inLon;
  	}
  
  	/** Constant pair to represent padding */
  	public static final CoordPair PADDING = new CoordPair(-1.0, -1.0);
  
  	/**
  	 * Try to parse the given pair of characters into a CoordPair
  	 * @param inFirst first character of pair
  	 * @param inSecond second character of pair
  	 * @return CoordPair from (0, 0) to (19/20, 19/20)
  	 * @throws ParseException
  	 */
  	public static CoordPair decode(char inFirst, char inSecond) throws ParseException
  	{
  		final boolean isFirstPadding = (inFirst == '0');
  		final boolean isSecondPadding = (inSecond == '0');
  		if (isFirstPadding && isSecondPadding) {return CoordPair.PADDING;}
  		if (isFirstPadding || isSecondPadding) {throw new ParseException();}
  		// Try to turn these characters into numbers
  		final double lat = decodeChar(inFirst);
  		final double lon = decodeChar(inSecond);
  		return new CoordPair(lat / 20.0, lon / 20.0);
  	}
  
  	/**
  	 * Try to parse the given single character into a CoordPair
  	 * @param inChar single character from level 11
  	 * @return CoordPair from (0, 0) to (19/20, 19/20)
  	 * @throws ParseException
  	 */
  	public static CoordPair decode(char inChar) throws ParseException
  	{
  		// Try to turn this character into a number
  		final int charIndex = decodeChar(inChar);
  		final int lat = charIndex / 4;
  		final int lon = charIndex % 4;
  		return new CoordPair(lat / 5.0, lon / 4.0);
  	}
  
  	/**
  	 * Get the index from the given character
  	 * @param inChar character from OLC
  	 * @return index from 0 to 19
  	 * @throws ParseException if character not found
  	 */
  	private static int decodeChar(char inChar) throws ParseException
  	{
  		final int index = ALPHABET.indexOf(inChar);
  		if (index < 0) {
  			throw new ParseException();
  		}
  		return index;
  	}
  
  	/**
  	 * Get the character for the given index
  	 * @param inValue from 0 to 19
  	 */
  	public static char encode(int inValue)
  	{
  		return ALPHABET.charAt((inValue + 20) % 20);
  	}
  }
  