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%  $Date: 2010-10-15 17:09:55 +0200 (Fri, 15 Oct 2010) $
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:- module(timer,[timer_start/1,    % +ID
		 timer_stop/2,     % +ID,-Duration
		 timer_pause/1,    % +ID
		 timer_pause/2,    % +ID,-Duration
		 timer_resume/1,   % +ID
		 timer_elapsed/2,  % +ID, -Duration
		 timer_reset/1]).  % +ID
:- yap_flag(unknown,error).
:- style_check(single_var).

:- dynamic(timer/2).
:- dynamic(timer_paused/2).


timer_start(Name) :-
	(
	 timer(Name,_)
	->
	 throw(timer_already_started(timer_start(Name)));

	 statistics(walltime,[StartTime,_]),
	 assertz(timer(Name,StartTime))
	).

timer_start_forced(Name) :-
	retractall(timer(Name,_)),
	statistics(walltime,[StartTime,_]),
	assertz(timer(Name,StartTime)).

timer_stop(Name,Duration) :-
	(
	 retract(timer(Name,StartTime))
	->
	 statistics(walltime,[StopTime,_]),
	 Duration is StopTime-StartTime;

	 throw(timer_not_started(timer_stop(Name,Duration)))
	).

timer_pause(Name) :-
  (
   retract(timer(Name,StartTime))
  ->
   statistics(walltime,[StopTime,_]),
   Duration is StopTime-StartTime,
   assertz(timer_paused(Name,Duration));

   throw(timer_not_started(timer_pause(Name)))
  ).

timer_pause(Name, Duration) :-
  (
   retract(timer(Name,StartTime))
  ->
   statistics(walltime,[StopTime,_]),
   Duration is StopTime-StartTime,
   assertz(timer_paused(Name,Duration));

   throw(timer_not_started(timer_pause(Name)))
  ).

timer_resume(Name):-
	(
	 retract(timer_paused(Name,Duration))
	->
	 statistics(walltime,[ResumeTime,_]),
	 CorrectedStartTime is ResumeTime-Duration,
	 assertz(timer(Name,CorrectedStartTime));
	 
	 throw(timer_not_paused(timer_resume(Name)))
	).

timer_elapsed(Name,Duration) :-
	(
	 timer(Name,StartTime)
	->
	 statistics(walltime,[StopTime,_]),
	 Duration is StopTime-StartTime;

	 throw(timer_not_started(timer_elapsed(Name,Duration)))
	).

timer_reset(Name) :-
	retractall(timer(Name,_)),
	retractall(timer_paused(Name,_)).