package layer;

import java.util.*;

/**
 * The abstract class LayersGroup holds a collection of layers and represents
 * any grouping of numerous layers.
 */
abstract class LayersGroup
{
    /**
     * A group of logically-connected layers.
     */
    static List<Layer> layers;
}

/**
 * The class AllLayers acts as a container holding all of the layers in-
 * use in the class.
 */
class AllLayers extends LayersGroup
{
}

/**
 * The class VisibleLayers acts as a container holding all of the layers
 * in a class that are visible to the whole class.
 */
class VisibleLayers extends LayersGroup
{
    /**
     * The makeVisible method makes a student's public layer visible to the
     * whole class by setting its isVisible boolean to true and placing it
     * in the VisibleLayers class's collection of Layers.
     * @param layer The Layer to show to the class.
     */
    /*@
     //
     // No requirements
     //
     
     ensures
     //
     // The layer should be added to the visible layers collection
     //
     layers.contains(layer);
    @*/
    static void makeVisible(PublicLayer layer){}

    /**
     * Hides a layer from the class.
     * @param layer The Layer to hide.
     */
    /*@
     requires
     //
     // Layer needs to be contained in the collection
     //
     layers.contains(layer);
     
     ensures
     //
     // The layer should be removed from the collection and all the other
     // layers should remain
     //
     !layers.contains(layer) &&
     (\forall Layer oldLayer ; \old(layers.contains(oldLayer)) ;
     oldLayer != layer <==> layers.contains(oldLayer));
    @*/
    static void hide(Layer layer) {}

    /**
     * Moves a layer to a different position relative to other Layers, which
     * changes how they appear on the screen.
     * @param layer The Layer to move.
     * @param position The desired location to move the Layer to (lower numbers
     * appear above higher numbers)
     */
    /*@
     requires
     //
     // Position needs to be a valid index in the collection,
     // and layer needs to be contained in the collection
     //
     (position >= 0 && position < layers.size())
     &&
     layers.contains(layer);
     
     ensures
     //
     // The layer should be in the desired position
     //
     (\forall int i ; i >= 0 && i < layers.size() ;
     ((i == position) <==> (layers.get(i) == layer)));
    @*/
    static void move(Layer layer, int position) {}
}