/**
 * Empty recursive list of objects.
 * @author Jeff Raab
 */
public class EmptyRecursiveList implements IList {

    /** Singleton empty list. */
    public static final EmptyRecursiveList EMPTY = new EmptyRecursiveList();
    
    /** Constructs an empty list. */
    private EmptyRecursiveList() {}

    /** Returns the first position in this. */
    public Position first() {
        throw new RuntimeException("List is empty");
    }
    
    /** Returns the last position in this. */
    public Position last() {
        throw new RuntimeException("List is empty");
    }
    
    /** 
     * 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) {
        throw new RuntimeException("Position not in list");
    }

    /** 
     * 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) {
        throw new RuntimeException("Position not in list");
    }
    
    /**
     * Returns whether or not the given position is first in this.
     * @param aPosition position to test
     */
    public boolean isFirst(Position aPosition) {
        return false;
    }

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

    /**
     * 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) {
        return new RecursiveList(anObject);
    }
    
    /**
     * 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) {
        return new RecursiveList(anObject);
    }
    
    /**
     * 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) {
        throw new RuntimeException("Position not in list");
    }

    /**
     * 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) {
        throw new RuntimeException("Position not in list");
    }
    
    /** Removes and returns the first element of this. */
    public IList removeFirst() {
        throw new RuntimeException("List is empty");
    }

    /** Removes and returns the last element of this. */
    public IList removeLast() {
        throw new RuntimeException("List is empty");
    }
    
    /** 
     * Removes the given position from this and returns its element.
     * @param aPosition position to remove
     */
    public IList remove(Position aPosition) {
        throw new RuntimeException("Position not in list");
    }
    
    /**
     * 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) {
        throw new RuntimeException("Position not in list");
    }

    /** Returns the size of this. */
    public int size() {
        return 0;
    }
    
    /** Returns whether or not this is empty. */
    public boolean isEmpty() {
        return true;
    }
}