package listFW.visitor;
import listFW.*;


/**
 * Merges the host and the input parameter inp into a sorted list.
 * Assumes host and inp are IList containing Integer sorted in ascending order.
 * @author DXN
 */
public class Merge implements IListAlgo {
    private listFW.IListFactory _fact;
    
    /**
     * This helper assumes the input parameter inp is a non=empty list.
     */
    private IListAlgo mergeHelp = new IListAlgo() {
        public Object emptyCase(IEmptyList host, Object inp){
            return inp;
        }
        
        /**
         * Now both host and inp are non-empty.
         */
        public Object nonEmptyCase(INEList host, Object inp){
            Integer f = (Integer)host.getFirst();
            Integer i = (Integer)((INEList)inp).getFirst();
            return f.intValue() < i.intValue()?
                _fact.makeNEList(f, (IList)host.getRest().execute(Merge.this, inp)):
                _fact.makeNEList(i, (IList)host.execute(Merge.this, ((INEList)inp).getRest()));
        }
    };
    
    public Merge(IListFactory f) {
        _fact = f;
    }
    
    public Object emptyCase(IEmptyList host, Object inp){
        return inp;
    }
                                                       
    public Object nonEmptyCase(INEList host, Object inp){
        return ((IList)inp).execute(mergeHelp, host);
    }
}