module Navigation;

from Lecture import all;
from Layers import all;
export all;

object SlideDB
	components: sli:Slide*;
	description: (*
		The database of slides.
		*);
end SlideDB;

object Slide
	components: leclay:LectureLayer and num:Number;
	operations: Next, Previous;
	description: (*
		Used to keep track of the position of the base layer, the lecture layer.
		*);
end Slide;

object Number
	components: integer;
	description: (*
		The number of a specific slide in the Slide Database.
		*);
end Number;

object CurrentSlide
	components: sli:Slide;
	description: (*
		The current slide being shown.
		*);
end CurrentSlide;

object Jump
	components: integer;
	description: (*
		Used to store the slide number to jump to using the GoTo function.
		*);
end Jump;

object Broadcast
	components: boolean;
	description: (*
		Whether the presentation is being broadcasted to student machines or not.
		*);
end Broadcast;

object SlideControl
	operations: Previous, First, Start, Last, Next, Goto;
	description: (*
		The slide control bar is the window from where the slides are controlled.
		*);
end SlideControl;

operation First
	inputs: slidb:SlideDB, cursli:CurrentSlide;
	outputs: slidb':SlideDB, cursli':CurrentSlide;
	precondition:(*
		There is at least one slide available.
		*)
		#slidb >= 1;
	postcondition:(*
		The LectureScreen displays the first slide.
		*)
		cursli.sli = slidb[1];
end First;

operation Start
	inputs: lecscr:LectureScreen;
	outputs: lecscr':LectureScreen;
	precondition:(*
		A lecture is loaded.
		*)
		lecscr != nil;
	postcondition:(*
		The lecture is broadcast to logged in student machines.
		*)
		lecscr.bro;
end Start;

operation Previous
	inputs: slidb:SlideDB, cursli:CurrentSlide;
	outputs: slidb':SlideDB, cursli':CurrentSlide;
	precondition:(*
		There is a previous slide available.
		*)
		cursli.sli.num > 1;
	postcondition:(*
		The LectureScreen displays the previous slide.
		*)
		cursli.sli = slidb[cursli.sli.num - 1];
end Previous;

operation Next
	inputs: slidb:SlideDB, cursli:CurrentSlide;
	outputs: slidb':SlideDB, cursli':CurrentSlide;
	precondition:(*
		There is a next slide available.
		*)
		cursli.sli.num < #slidb - 1;
	postcondition:(*
		The LectureScreen displays the next slide.
		*)
		cursli.sli = slidb[cursli.sli.num + 1];
end Next;

operation Goto
	inputs: slidb:SlideDB, cursli:CurrentSlide, jum:Jump;
	outputs: slidb':SlideDB, cursli':CurrentSlide;
	precondition:(*
		There is at least one slide available and the integer is within range.
		*)
		#slidb >= 1 and jum < #slidb and jum >= 1;
	postcondition:(*
		The LectureScreen displays the selected slide;
		*)
		cursli.sli = slidb[jum];
end Goto;

end Navigation;