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#ifndef MESSAGE_FILTERS_TIME_SEQUENCER_H
#define MESSAGE_FILTERS_TIME_SEQUENCER_H

#include <ros/ros.h>

#include "connection.h"
#include "simple_filter.h"

namespace message_filters
{

/**
 * \class TimeSequencer
 *
 * \brief Sequences messages based on the timestamp of their header.
 *
 * The TimeSequencer object is templated on the type of message being sequenced.
 *
 * \section behavior BEHAVIOR

 * At construction, the TimeSequencer takes a ros::Duration
 * "delay" which specifies how long to queue up messages to
 * provide a time sequencing over them.  As messages arrive they are
 * sorted according to their time stamps.  A callback for a message is
 * never invoked until the messages' time stamp is out of date by at
 * least delay.  However, for all messages which are out of date
 * by at least delay, their callback are invoked and guaranteed
 * to be in temporal order.  If a message arrives from a time \b prior
 * to a message which has already had its callback invoked, it is
 * thrown away.
 *
 * \section connections CONNECTIONS
 *
 * TimeSequencer's input and output connections are both of the same signature as roscpp subscription callbacks, ie.
\verbatim
void callback(const boost::shared_ptr<M const>&);
\endverbatim
 *
 */
template<class M>
class TimeSequencer : public SimpleFilter<M>
{
public:
  typedef boost::shared_ptr<M const> MConstPtr;
  typedef ros::MessageEvent<M const> EventType;

  /**
   * \brief Constructor
   * \param f A filter to connect this sequencer's input to
   * \param delay The minimum time to hold a message before passing it through.
   * \param update_rate The rate at which to check for messages which have passed "delay"
   * \param queue_size The number of messages to store
   * \param nh (optional) The NodeHandle to use to create the ros::Timer that runs at update_rate
   */
  template<class F>
  TimeSequencer(F& f, ros::Duration delay, ros::Duration update_rate, uint32_t queue_size, ros::NodeHandle nh = ros::NodeHandle())
  : delay_(delay)
  , update_rate_(update_rate)
  , queue_size_(queue_size)
  , nh_(nh)
  {
    init();
    connectInput(f);
  }

  /**
   * \brief Constructor
   *
   * This version of the constructor does not take a filter immediately.  You can connect to a filter later with the connectInput() function
   *
   * \param delay The minimum time to hold a message before passing it through.
   * \param update_rate The rate at which to check for messages which have passed "delay"
   * \param queue_size The number of messages to store
   * \param nh (optional) The NodeHandle to use to create the ros::Timer that runs at update_rate
   */
  TimeSequencer(ros::Duration delay, ros::Duration update_rate, uint32_t queue_size, ros::NodeHandle nh = ros::NodeHandle())
  : delay_(delay)
  , update_rate_(update_rate)
  , queue_size_(queue_size)
  , nh_(nh)
  {
    init();
  }

  /**
   * \brief Connect this filter's input to another filter's output.
   */
  template<class F>
  void connectInput(F& f)
  {
    incoming_connection_.disconnect();
    incoming_connection_ = f.registerCallback(typename SimpleFilter<M>::EventCallback(boost::bind(&TimeSequencer::cb, this, _1)));
  }

  ~TimeSequencer()
  {
    update_timer_.stop();
    incoming_connection_.disconnect();
  }

  void add(const EventType& evt)
  {
    namespace mt = ros::message_traits;

    boost::mutex::scoped_lock lock(messages_mutex_);
    if (mt::TimeStamp<M>::value(*evt.getMessage()) < last_time_)
    {
      return;
    }

    messages_.insert(evt);

    if (queue_size_ != 0 && messages_.size() > queue_size_)
    {
      messages_.erase(*messages_.begin());
    }
  }

  /**
   * \brief Manually add a message to the cache.
   */
  void add(const MConstPtr& msg)
  {
    EventType evt(msg);
    add(evt);
  }

private:
  class MessageSort
  {
  public:
    bool operator()(const EventType& lhs, const EventType& rhs) const
    {
      namespace mt = ros::message_traits;
      return mt::TimeStamp<M>::value(*lhs.getMessage()) < mt::TimeStamp<M>::value(*rhs.getMessage());
    }
  };
  typedef std::multiset<EventType, MessageSort> S_Message;
  typedef std::vector<EventType> V_Message;

  void cb(const EventType& evt)
  {
    add(evt);
  }

  void dispatch()
  {
    namespace mt = ros::message_traits;

    V_Message to_call;

    {
      boost::mutex::scoped_lock lock(messages_mutex_);

      while (!messages_.empty())
      {
        const EventType& e = *messages_.begin();
        ros::Time stamp = mt::TimeStamp<M>::value(*e.getMessage());
        if (stamp + delay_ <= ros::Time::now())
        {
          last_time_ = stamp;
          to_call.push_back(e);
          messages_.erase(messages_.begin());
        }
        else
        {
          break;
        }
      }
    }

    {
      typename V_Message::iterator it = to_call.begin();
      typename V_Message::iterator end = to_call.end();
      for (; it != end; ++it)
      {
        this->signalMessage(*it);
      }
    }
  }

  void update(const ros::TimerEvent&)
  {
    dispatch();
  }

  void init()
  {
    update_timer_ = nh_.createTimer(update_rate_, &TimeSequencer::update, this);
  }

  ros::Duration delay_;
  ros::Duration update_rate_;
  uint32_t queue_size_;
  ros::NodeHandle nh_;

  ros::Timer update_timer_;

  Connection incoming_connection_;


  S_Message messages_;
  boost::mutex messages_mutex_;
  ros::Time last_time_;
};

}

#endif
