module LectureOperations;

from Lecture import all;
export all;

object MaxSlideNumber is int;
   description: (* The number of a slides in a LectureElement. *);
end MaxSlideNumber;

object ToSlideNumber is int;
   description: (* The slide number to advance to. *);
end MaxSlideNumber;

operation nextSlide is
   inputs: sn : SlideNumber, msn: MaxSlideNumber;
   output: sn': SlideNumber;
   description: (* The next slide is advanced to using the page toolbar. *);
   precondition: (* cannot advance to the next slide if at the end *)
		  #sn < msn;
   postcondition: (* The slide number increments by 1 *)
	          #sn' = #sn + 1;
end nextSlide;

operation prevSlide is
   inputs: sn : SlideNumber;
   output: sn': SlideNumber;
   description: (* The previous slide is advanced to using the page toolbar. *);
   precondition: (* cannot advance to the previous slide if at the first slide *)
	          #sn > 1;
   postcondition: (* The slide number decreases by 1 *)
                  #sn' = #sn + 1;
end nextSlide;

operation lastSlide is
   inputs: sn : SlideNumber, msn: MaxSlideNumber;
   output: sn': SlideNumber;
   description: (* The last slide is advanced to using the page toolbar. *);
   precondition: (* none *);
   postcondition: (* The slide number increases to the maximum slide number *)
                  #sn = msn;
end lastSlide;

operation firstSlide is
   inputs: sn : SlideNumber;
   output: sn': SlideNumber;
   description: (* The first slide is advanced to using the page toolbar. *);
   precondition: (* none *);
   postcondition: (* The slide number is 1. *)
                  #sn = 1;
end firstSlide;

operation toSlide is
   inputs: sn : SlideNumber, msn: MaxSlideNumber, tsn: ToSlideNumber;
   output: sn': SlideNumber;
   description: (* The slide is advanced to the number entered using the page toolbar. *);
   precondition: (* slide number entered is within range *)
                 (tsn >=1) and (tsn <= msn);
   postcondition: (* The slide number is advanced to the entered number. *)
                  #sn = tsn;
end toSlide;

end LectureOperations;