package listFW.visitor;
import listFW.*;

/**
 * Computes a String reprsentation of IList showing  a left parenthesis followed
 * by elements of the IList separated by commas, ending with with a right parenthesis.
 * This code has been written to make it run on any list.
 * @stereotype visitor
 * @author D.X. Nguyen, S. Wong
 * @since 07/01/2004
 * @author Mathias Ricken - Copyright 2008 - All rights reserved.
 */
public class ToStringAlgo implements IListAlgo<Object, String, Object> {
    
    public static final ToStringAlgo Singleton = new ToStringAlgo();
    private ToStringAlgo() {
    }
    
    /**
     * Returns "()".
     */
    public String emptyCase(IMTList<? extends Object> host, Object ... inp) {
        return "()";
    }
    
    /**
     * Passes "(" + first to the rest of IList and asks for help to complete the computation.
     */
    public String nonEmptyCase(INEList<? extends Object> host, Object ... inp) {
        return host.getRest().execute(ToStringHelper.Singleton, "(" + host.getFirst());
    }
}

/**
 * Helps ToStringAlgo compute the String representation of the rest of the list.
 */
class ToStringHelper implements IListAlgo<Object, String, String> {
    public static final ToStringHelper Singleton = new ToStringHelper();
    private ToStringHelper() {
    }
    
    /**
     * Returns the accumulated String + ")".
     * At end of list: done!  
     */
    public String emptyCase(IMTList<? extends Object> host, String ... acc) {
        return  acc[0] + ")";
    }
    
    /**
     * Continues accumulating the String representation by appending ", " + first to acc
     * and recur!
     */
    public String nonEmptyCase(INEList<? extends Object> host, String ... acc) {
        return host.getRest().execute(this, acc[0] + ", " + host.getFirst());
    }
}