/***********************************************
 *  CS2510 Spring 2011 
 *  Lecture #19 Afternoon
 *  A Queue with 2 Stacks
 ***********************************************/

import tester.*;
import image.*;
import world.*;
import java.util.ArrayList;


/** Represents a <blink>Stack</blink> using an <marquee>ArrayList</marquee> */
class Stack<X>{
    ArrayList<X> stack = new ArrayList<X>();

    /** Push the given element onto the top of this Stack */
    void push(X x){
        this.stack.add(x);
    }
    /** Take a look at this stack's top element */
    X peek(){
        return this.stack.get(this.stack.size()-1);
    }
    /** Remove (and return) this stack's top element */
    X pop(){
        return this.stack.remove(this.stack.size()-1);
    }
    /** Does this stack have any elements? */
    boolean isEmpty(){
        return this.stack.isEmpty();
    }
}

/** Implement a <blink>Queue</blink> using two <marquee>Stacks</marquee>*/
class Queue<W>{
    Stack<W> inStk = new Stack<W>();
    Stack<W> outStk = new Stack<W>();
    
    /** Add the given element to the "back" of this Queue */
    void enqueue(W w){
        this.inStk.push(w);
    }
    
    /** Helper to shift the in" */
    private void restack(){
        // Move all the elements from the inStk to the outStack
        if(!this.inStk.isEmpty()){
            this.two.push(this.one.pop());
            this.restack();
        }
    }
    
    /** Remove (and return) an element from the "front" of this Queue */
    W dequeue(){
        // No Elements!
        if(this.isEmpty()){
            throw new Mimi("Bad News!");
        }
        // No outStk elements... move them from the inStk
        if(this.outStk.isEmpty()){
            this.restack();
        }
        // Must succeed! :)
        return this.outStk.pop();
    }
    /** Look at the element at the "front" of this Queue */
    W front(){
        // No Elements!
        if(this.isEmpty()){
            throw new Mimi("Bad News!");
        }
        // No outStk elements... move them from the inStk        
        if(this.outStk.isEmpty()){
            this.restack();
        }
        return this.outStk.peek();
    }
    /** Does this queue have any elements? */
    boolean isEmpty(){
        return this.inStk.isEmpty() && this.outStk.isEmpty();
    }
}

/** Represents a custom error condition */
class Mimi extends RuntimeException{
    Mimi(String msg){
        super(msg);
    }
}

/** Examples and Tests */
class LectureExamples{

    void testQueue(Tester t){
        Queue<Double> q = new Queue<Double>();
        
        q.enqueue(2.5);
        q.enqueue(4.0);
        q.enqueue(105.1);
        q.enqueue(19.69);
        
        t.checkExpect(q.front(), 2.5);
        t.checkExpect(q.dequeue(), 2.5);
        t.checkExpect(q.front(), 4.0);
        t.checkExpect(q.dequeue(), 4.0);
        t.checkExpect(q.isEmpty(), false);

        q.dequeue();
        q.dequeue();
        t.checkExpect(q.isEmpty(), true);
    }
}