// timer.h
//
// by David Hershberger, 11-12-95
//
// Timer class is intended to allow the users of it to register a
// callback which will happen every nth time we get a timer interrupt,
// where n is configurable.

#ifndef TIMER_H
#define TIMER_H

#include <stdio.h>

struct Callback{
  Callback *next;
  void (* function)(double elapsed_time);
  int tick_count;
  int num_ticks;
};

// To derive a usable subclass from the abstract Timer class, override
// only those items marked for overriding in the class definition
// below.

// For a sample derived class, see clemtime.h and clemtime.cpp.

class Timer{

private:
  int changing_list;
  int doing_callback_list;
  Callback *doing_this_callback;
  Callback *callback_list;
  virtual void setup();
  friend void timer_handler();

protected:
  double tick_interval;

  virtual void install_timer_handler(void(*)()) = 0; // override
  virtual void set_tick_interval() = 0;       // override
  
public:
  Timer();
  virtual ~Timer();
  virtual double read_tick_interval();
  virtual void add_callback(void (* callback_fn)(double elapsed_time),
			    int numticks, int offset);
  virtual void delete_callback(void (* callback_fn)(double
						    elapsed_time),
			       int numticks);

  virtual void close() = 0; // override. close() should uninstall the
			    // timer handler
};

// There is only one timer per computer, so declare it a global
// constant. Define it not in timer.cpp, but in clemtimer.cpp or
// whereever the computer-specific version is derived.
extern Timer * const timer;

#endif				// TIMER_H