gistfile1.java

public class PeriodEntries<T extends Timestamped> implements Iterable<List<T>> {
  private final Iterator<List<T extends Timestamped>> entriesIt;
  private final long interval;
  private PeriodEntries(Iterable<List<T>> entriesIt, long interval) {
    this.entriesIt = entriesIt.iterator();
    this.interval = interval;
  }

  public static <T extends Timestamped> PeriodEntries<T> create(Iterable<List<T>> entriesIt, long interval) {
   return new PeriodEntries<T>(entriesIt, interval);
  }
 
  @Override
  public Iterator<List<T extends Timestamped>> iterator() {
    return new Iterator<List<T>>() {
      private Queue<List<T>> queue = new LinkedList<List<T>>();
      private long previous;
      private Iterator<T> entryIt;
 
      @Override
      public boolean hasNext() {
        if (!advanceEntries()) {
          return false;
        }
        T entry =  entryIt.next();
        long time = normalizeInterval(entry);
        if (previous == 0) {
          previous = time;
        }
        if (queue.peek() == null) {
          List<T> group = new ArrayList<T>();
          queue.add(group);
        }
        while (previous == time) {
          queue.peek().add(entry);
          if (!advanceEntries()) {
            break;
          }
          entry = entryIt.next();
          time = normalizeInterval(entry);
        }
        previous = time;
        List<T> result = queue.peek();
        if (result == null || result.isEmpty()) {
          return false;
        }
        return true;
      }
 
      private boolean advanceEntries() {
        // if there are no rows left
        if (entryIt == null || !entryIt.hasNext()) {
          // try get more rows if possible
          if (entriesIt.hasNext()) {
            entryIt = entriesIt.next().iterator();
            return true;
          } else {
            // no more rows
            return false;
          }
        }
        return true;
      }
 
      private long normalizeInterval(Timestamped entry) {
        long time = entry.getTime();
        int utcOffset = TimeZone.getDefault().getOffset(time);
        long utcTime = time + utcOffset;
        long elapsed = utcTime % interval;
        return time - elapsed;
      }
      @Override
      public List<T> next() {
        return queue.poll();
      }
      @Override
      public void remove() {
        throw new UnsupportedOperationException();
      }
   };
  }
}