////////////////////////////////////
// MT3Q1.cpp - Priority Queue

#include <iostream>
#include <queue>

enum Priority { High, Low };

class msg
{
public:
  msg(std::string m="", Priority p=Low) : _p(p), _m(m) {}
  msg(const msg& m) : _p(m._p), _m(m._m) {}
  Priority priority() { return _p; }
  operator std::string () { return _m; }
  bool IsNull() { return _m.compare("") == 0; }
  msg& operator=(const msg& m)
  {
    if(this == &m) return *this;
    _p = m._p;
    _m = m._m;
    return *this;
  }
private:
  Priority _p;
  std::string _m;
};


class PriorityQueue
{
public:
  void enQ(msg& m)
  {
    switch(m.priority())
    {
    case High: hi.push(m); return;
    case Low:  lo.push(m); return;
    }
  }

  msg deQ()
  {
    msg temp("");
    if(hi.size() > 0)
    {
      temp = hi.front(); hi.pop(); return temp;
    }
    else if(lo.size() > 0)
    {
      temp = lo.front(); lo.pop(); return temp;
    }
    return temp;
  }
  size_t size() { return hi.size() + lo.size(); }
private:
  std::queue<msg> hi;  // queues have correct copy and assignment so
  std::queue<msg> lo;  // compiler generated copy and assignment work 
};
//
void main()
{
  PriorityQueue pq;
  std::cout << "\n  # msgs in queue: " << pq.size();
  msg mHi("high priority message",High);
  msg mLo("Low priority message",Low);

  std::cout << "\n  pushing hi priority msg";
  pq.enQ(mHi);
  std::cout << "\n  pushing lo priority msg";
  pq.enQ(mLo);
  std::cout << "\n  pushing hi priority msg";
  pq.enQ(mHi);
  std::cout << "\n  # msgs in queue: " << pq.size();

  msg m;
  do
  {
    m = pq.deQ();
    std::cout << "\n  " << static_cast<std::string>(m).c_str();
  } while(pq.size() > 0);

  std::cout << "\n  # msgs in queue: " << pq.size();
  std::cout << "\n\n";
}