/**
 * A Log collects and performs computations on LogRecords.  This is
 * an interface because we may implement logs different, e.g. as
 * a local array, as a Collection, as a remote server or database, etc.
 */
public interface Log {
  /**
   * Stores a LogRecord in the Log if it matches the current
   * filter (as set by setFilter, below).
   */
  public void add(LogRecord record);
  
  /**
   * Returns all LogRecords whose timestamps are within a window of
   * time.  Note that inclusion is based on the timestamp of the
   * LogRecord, not the time at which the record was stored in the
   * Log.
   *
   * @param windowMS return all records from the last [windowMS]
   * milliseconds.
   */
  public LogRecord[] getAll(long windowMS);

  /**
   * Sets a regular-expression filter on what events are stored.
   *
   * @param pattern is a regular expression to match against; if the
   * event portion of a LogRecord passed to add, above, matches this
   * expression, then the LogRecord is retained, and is otherwise
   * discarded.
   */
   public void setFilter(String pattern);
}