// A Java implementation of VendingMachine.
// Original in C++ by Liu Ling.
// Taken from a paper by Mary Jean Harrold.
// Translated to Java by Jeff Offutt, January 2004
// Main added later for testing

import java.util.*;
import java.io.*;

public class vendingMachine
{
private int credit;
private LinkedList stock;
String Choc = "";

// Maximum size of vendingMachine
private static final int MAX = 10;

// In the C++ version, Ling used a C++ list<string>
// with operations like push(), pop(), etc to look
// a lot like a queue.
// list<string> stock; ??
// In the Java version I'm emulating a queue on
// top of the LinkedList.

//************************************************
// Constructor
// vendingmachine starts empty.
//************************************************
vendingMachine()
{
   credit = 0;
   stock  = new LinkedList(); // Empty stock.
}

//************************************************
// A coin is given to the vendingMachine.
// Must be a dime, quarter or dollar.
// Ignores invalid input
//************************************************
public void coin (int coin)
{
   if (coin != 10 && coin != 25 && coin != 100)
      return;
   if (credit >= 90)
      return;
   credit = credit + coin;
   return;
}

//************************************************
// User asks for a chocolate.
// Returns the change and the sets the
// parameter StringBuffer variable Choc.
// If not enough money or no chocolates,
// returns 0 and a blank string.
//************************************************
// Necessary because strings are immutable
// C++ version returned both choc and change as parameters
public int getChoc (StringBuffer choc)
{
   int change;

   if (credit < 90 || stock.size() <= 0)
   {
      change = 0;
      choc.replace (0, choc.length(), "");
      return (change);
   }
   change = credit - 90;
   credit = 0;

   choc.replace (0, choc.length(), (String) stock.removeFirst());

   return (change);
}

//************************************************
// Adds one new piece of chocolate to the machine
// If machine is full, nothing happens
//************************************************
public void addChoc (String choc)
{
   if (stock.size() >= MAX)
      return;
   stock.add (choc);
   return;
}

// Needed for testing
public int getCredit ()
{
   return (credit);
}


// Needed for testing
public LinkedList getStock ()
{
   return (stock);
}

} // End class vendingMachine