package org.opentrafficsim.core.perception;
   
   import org.djunits.value.vdouble.scalar.Time;
   import org.djutils.exceptions.Throw;
   import org.opentrafficsim.core.perception.AbstractHistorical.EventValue;
   
   /**
    * Single-valued historical state.
    * <p>
   * Copyright (c) 2013-2019 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="http://opentrafficsim.org/node/13">OpenTrafficSim License</a>.
   * <p>
   * @version $Revision$, $LastChangedDate$, by $Author$, initial version 1 jan. 2018 <br>
   * @author <a href="http://www.tbm.tudelft.nl/averbraeck">Alexander Verbraeck</a>
   * @author <a href="http://www.tudelft.nl/pknoppers">Peter Knoppers</a>
   * @author <a href="http://www.transport.citg.tudelft.nl">Wouter Schakel</a>
   * @param <T> value type
   */
  public class HistoricalValue<T> extends AbstractHistorical<T, EventValue<T>> implements Historical<T>
  {
  
      /** Store last value for quick access. */
      private T lastValue;
  
      /** Store last time for quick access. */
      private double lastTime;
  
      /**
       * Constructor.
       * @param historyManager HistoryManager; history manager
       */
      public HistoricalValue(final HistoryManager historyManager)
      {
          super(historyManager);
      }
  
      /**
       * Constructor.
       * @param historyManager HistoryManager; history manager
       * @param initialValue T; initial value
       */
      public HistoricalValue(final HistoryManager historyManager, final T initialValue)
      {
          super(historyManager);
          set(initialValue);
      }
  
      /** {@inheritDoc} */
      @Override
      public final void set(final T value)
      {
          this.lastValue = value;
          this.lastTime = now().si;
          EventValue<T> event = getLastEvent();
          if (event != null && event.getTime() == this.lastTime)
          {
              removeEvent(event);
          }
          addEvent(new EventValue<>(this.lastTime, value));
      }
  
      /** {@inheritDoc} */
      @Override
      public final T get()
      {
          return this.lastValue;
      }
  
      /** {@inheritDoc} */
      @Override
      public final T get(final Time time)
      {
          Throw.whenNull(time, "Time may not be null.");
          if (time.si >= this.lastTime)
          {
              return this.lastValue;
          }
          EventValue<T> event = getEvent(time);
          return event == null ? null : event.getValue();
      }
  
      /** {@inheritDoc} */
      @Override
      public String toString()
      {
          return "HistoricalValue [current=" + get() + "]";
      }
  
  }