/* Code of Figure 10.10, pages 435-436
   and Figure 10.11, page 437, from
   Kenneth C. Louden, Programming Languages
   Principles and Practice 2nd Edition
   Copyright (C) Brooks-Cole/ITP, 2003
   Test code from pages 438 and 429 also added
*/

#include <iostream>
using std::cout;
using std::endl;

// Figure 10.10 code
class LinkableObject
{
public:
  LinkableObject()
  : link(0) { }

  LinkableObject (LinkableObject* p)
  : link(p) { }

  LinkableObject* next()
  { return link; }

  void linkTo( LinkableObject* p)
  { link = p; }

private:
  LinkableObject* link;
};

// Figure 10.11 code
class Queue
{
public:
  Queue() : rear(0) { }

  bool empty() // corrected from int
  { return rear == 0; }

  void enqueue(LinkableObject* item);

  void dequeue();

  LinkableObject* front()
  { return rear->next(); }

  ~Queue();

protected: // demo - may not be appropriate
    LinkableObject* rear;
 };

void Queue::enqueue(LinkableObject* item)
{ if (empty())
  { rear = item;
    rear->linkTo(item);
  }
  else
  { item->linkTo(front());
    rear->linkTo(item);
    rear = item;
  }
}

void Queue::dequeue()
{ if (front() == rear) rear = 0;
  else rear->linkTo(front()->next());
}

Queue::~Queue()
// demo code - may result in dangling refs
{ while (!empty())
  { LinkableObject* temp = front();
    dequeue();
    delete temp;
  }
}

// Code from page 439
class LinkableInt : public LinkableObject
{
public:
  LinkableInt(int d) : item(d) { }

  int data() 
  { return item; }

private:
  int item;
};

// test code from pages 438 and 439
int main()
{ Queue q;
  LinkableObject* x = new LinkableObject;
  q.enqueue(x);
  q.enqueue(new LinkableObject);
  LinkableObject* y = q.front(); // now y is x
  if (y == x) cout << "ok!\n";
  else cout << "oops!\n";
  q.dequeue();
  q.dequeue(); // q is now empty
  if (q.empty()) cout << "ok!" << endl;
  else cout << "oops!" << endl;

  { // page 439
    LinkableInt* x = new LinkableInt(42);
    q.enqueue(x);
    x = static_cast<LinkableInt*>(q.front());
    cout << x->data() << endl; // prints 42
  }
  return 0;
}