package presentation;

import java.util.Collection;
import java.util.List;

/**
 * The Presentation document is derived primarily from section 2.2
 * of the requirements, and is the central document in E-Class.
 * A Presentation contains both slides and topics, which are linked
 * to each other.
 * <p>
 * A Presentation also maintains the index of the currently viewed
 * slide, and provides operations to change slides. These are derived
 * from sections 2.3.2, 2.3.3 and 2.4.1 of the requirements.
 */
public abstract class Presentation {
    /** Slides in the presentation. */
    List<Slide> slides;
    /** All topics in the presentation (interrelated in a tree structure). */
    List<Topic> topics;
    /** Which slide is currently viewed, an index into 'slides'. */
    int currentSlide;

    /**
     * Advances the presentation to the next slide. 
     */
    /*@
     requires
      //
      //The current slide is not the last slide in the presentation
      //
         (currentSlide < slides.size());

      ensures
      //
      //If the presentation is not at the last slide, it advances to the next slide
      //
         (currentSlide == \old(currentSlide) + 1);
    */
    abstract void nextSlide();

    /**
     * Moves the presentation to the previous slide. 
     */
    /*@
     requires
      //
      //The current slide is not the first slide in the presentation
      //
         (currentSlide != 0);

      ensures
      //
      //If the presentation is not at the first slide, it moves to the previous slide
      //
         (currentSlide == \old(currentSlide) - 1);
    */
    abstract void prevSlide();

    /**
     * Moves the presentation to the first slide. 
     */
    /*@
     requires
      //
      //The current slide is not the first slide in the presentation
      //
         (currentSlide > 0);

      ensures
      //
      //If the presentation is not at the first slide, it moves to the first slide
      //
         (currentSlide == 0);
    */
    abstract void firstSlide();

    /**
     * Advances the presentation to the last slide. 
     */
    /*@
     requires
      //
      //The current slide is not the last slide in the presentation
      //
         (currentSlide < slides.size() - 1);

      ensures
      //
      //If the presentation is not at the last slide, it advances to the last slide
      //
         (currentSlide == slides.size() - 1);
    */
    abstract void lastSlide();

    /**
     * Advances the presentation to a given indexed slide. 
     */
    /*@
     requires
      //
      //The slide index given is within the bounds of the presentation
      //
         (0 <= slide && slide < slides.size());

      ensures
      //
      //If the presentation is not at the indexed slide, it advances to the indexed slide
      //
         (currentSlide == slide);
    */
    abstract void goToSlide(int slide);

    /**
     * Advances the presentation to the slide associated with a given topic. 
     */
    /*@
     requires
      //
      //The topic is a valid topic and has associated slides
      //
         (topics.contains(topic) == true);

      ensures
      //
      //If the presentation is not at the current topic, it advances to the current topic
      //
         (slides.get(currentSlide) == topic.slide);
    */
    abstract void goToTopic(Topic topic);

    /**
     * Breaks a slide into two, starting with a specified topic.
     */
    /*@
     requires
     // The requested index refers to an existing slide
     (0 <= slide) && (slide < slides.size())
     &&
     // The requested index refers to a valid topic on that slide
     (0 <= topic) && (topic < slides.get(slide).topics.size());

     ensures
     // The indicated topic and later topics on the slide are on a new slide
     (\forall int i; i >= topic && i < \old(slides.get(slide).topics.size());
        slides.get(slide + 1).topics.contains(\old(slides.get(slide).topics.get(i))))
     &&
     // and all other topics are still on the same slides.
     (\forall Topic t; topics.contains(t) && ! \old(slides.get(slide).topics.contains(t));
        t.slide == \old(t.slide));
    */
    abstract void breakSlide(int slide, int topic);

    /**
     * Imports a presentation from an HTML file, as described in
     * <a href="../../../requirements/usecase-importpresentation.html">
     * section 2.2.2</a> of the requirements.
     */
    static Presentation importHTML(String filename) {return null;}

    /**
     * Saves the presentation content to a file.
     */
    abstract void saveToFile(String filename);
}