/**
 * Circular IList implementation that uses an IList to store its elements.
 * @author Jeff Raab
 */
public class CircularIList implements IList {
    
    /** IList used to store elements of this. */
    protected IList elements;
    
    /**
     * Constructs a circular list 
     * that uses the given list to store its elements.
     * @param aList list used to store the elements
     */
    public CircularIList(IList aList) {
        elements = aList;
    }
    
    /** Returns the first position in this. */
    public Position first() {
        return elements.first();
    }
    
    /** Returns the last position in this. */
    public Position last() {
        return elements.last();
    }
    
    /** 
     * Returns the position in this 
     * that comes before the given position.
     * @param aPosition position for which previous position is desired
     */
    public Position before(Position aPosition) {
        if (isFirst(aPosition)) {
            return last();
        }
        
        return elements.before(aPosition);
    }

    /** 
     * Returns the position in this 
     * that comes before the given position.
     * @param aPosition position for which previous position is desired
     */
    public Position after(Position aPosition) {
        if (isLast(aPosition)) {
            return first();
        }
        
        return elements.after(aPosition);
    }
    
    /**
     * Returns whether or not the given position is first in this.
     * @param aPosition position to test
     */
    public boolean isFirst(Position aPosition) {
        return elements.isFirst(aPosition);
    }

    /**
     * Returns whether or not the given position is last in this.
     * @param aPosition position to test
     */
    public boolean isLast(Position aPosition) {
        return elements.isLast(aPosition);
    }

    /**
     * Inserts the given object at the beginning of this,
     * increasing the size of this by 1.
     * @param anObject object to insert
     */
    public IList insertFirst(Object anObject) {
        elements = elements.insertFirst(anObject);

        return this;
    }
    
    /**
     * Inserts the given object at the end of this,
     * increasing the size of this by 1.
     * @param anObject object to insert
     */
    public IList insertLast(Object anObject) {
        elements = elements.insertLast(anObject);

        return this;
    }
    
    /**
     * Inserts the given object before the given position in this, 
     * increasing the size of this by 1.
     * @param aPosition position to insert before
     * @param anObject object to insert
     */
    public IList insertBefore(Position aPosition, Object anObject) {
        elements = elements.insertBefore(aPosition, anObject);

        return this;
    }

    /**
     * Inserts the given object after the given position in this, 
     * increasing the size of this by 1.
     * @param aPosition position to insert before
     * @param anObject object to insert
     */
    public IList insertAfter(Position aPosition, Object anObject) {
        elements = elements.insertAfter(aPosition, anObject);

        return this;
    }
    
    /** Removes the first element of this. */
    public IList removeFirst() {
        elements = elements.removeFirst();

        return this;
    }

    /** Removes the last element of this. */
    public IList removeLast() {
        elements = elements.removeLast();
        
        return this;
    }
    
    /** 
     * Removes the given position from this.
     * @param aPosition position to remove
     */
    public IList remove(Position aPosition) {
        elements = elements.remove(aPosition);
        
        return this;
    }
    
    /**
     * Returns the element in the given position of this
     * and replaces it with the given object.
     * @param aPosition position of element to replace
     * @param anObject object to store in the given position
     */
    public Object replaceElement(Position aPosition, Object anObject) {
        return elements.replaceElement(aPosition, anObject);
    }

    /** Returns the size of this. */
    public int size() {
        return elements.size();
    }
    
    /** Returns whether or not this is empty. */
    public boolean isEmpty() {
        return elements.isEmpty();
    }
}