package au.gov.amsa.util.nmea;
   
   import java.util.Arrays;
   import java.util.LinkedHashMap;
   
   import org.apache.commons.lang3.StringUtils;
   
   import com.google.common.collect.Maps;
   
  /**
   * Parses NMEA messages.
   * 
   */
  public class NmeaMessageParser {
  
      private static final String CHECKSUM_DELIMITER = "*";
      private static final String PARAMETER_DELIMITER = ",";
      private static final String CODE_DELIMITER = ":";
  
      /**
       * Return an {@link NmeaMessage} from the given NMEA line.
       * 
       * @param line
       * @return
       */
      public NmeaMessage parse(String line) {
          LinkedHashMap<String, String> tags = Maps.newLinkedHashMap();
  
          String remaining;
          if (line.startsWith("\\")) {
              int tagFinish = line.lastIndexOf('\\', line.length() - 1);
              if (tagFinish == -1)
                  throw new NmeaMessageParseException(
                          "no matching \\ symbol to finish tag block: " + line);
              if (tagFinish == 0)
                  throw new NmeaMessageParseException("tag block is empty or not terminated");
              tags = extractTags(line.substring(1, tagFinish));
              remaining = line.substring(tagFinish + 1);
          } else
              remaining = line;
  
          String[] items;
          String checksum;
          if (remaining.length() > 0) {
              if (!remaining.contains("*"))
                  throw new NmeaMessageParseException("checksum delimiter * not found");
              items = getNmeaItems(remaining);
              // TODO validate message using checksum
              checksum = line.substring(line.indexOf('*') + 1);
          } else {
              items = new String[] {};
              // TODO decide what value to put here
              checksum = "";
          }
  
          return new NmeaMessage(tags, Arrays.asList(items), checksum);
      }
  
      /**
       * Returns the items from the comma delimited NMEA line. The last item
       * always contains a * followed by a checksum. If * is not present
       * {@link IndexOutOfBoundsException} will be thrown.
       * 
       * @param line
       * @return
       */
      private static String[] getNmeaItems(String line) {
          String[] items = StringUtils.splitByWholeSeparatorPreserveAllTokens(line,
                  PARAMETER_DELIMITER);
          // remove the checksum from the end
          String last = items[items.length - 1];
          if (last.contains("*"))
              items[items.length - 1] = last.substring(0, last.lastIndexOf('*'));
          return items;
      }
  
      /**
       * Returns the tags from the tag block section of the message (NMEA v4.0).
       * If there is no tag block then returns an empty map.
       * 
       * @param s
       * @return
       */
      public static LinkedHashMap<String, String> extractTags(String s) {
          LinkedHashMap<String, String> map = Maps.newLinkedHashMap();
          int c = s.lastIndexOf(CHECKSUM_DELIMITER);
          if (c == -1) {
              return map;
          }
          s = s.substring(0, c);
          String[] items = s.split(PARAMETER_DELIMITER);
          for (String item : items) {
              int i = item.indexOf(CODE_DELIMITER);
              if (i == -1)
                  throw new NmeaMessageParseException(
                          "TAG BLOCK parameter is not is format 'a:b' :" + s);
              map.put(item.substring(0, i), item.substring(i + 1));
          }
          return map;
     }
 }