// Purpose.  Adapter design pattern demo
// 
// Discussion.  LegacyRectangle's interface is not compatible with the
// system that would like to reuse it.  An abstract base class is created
// that specifies the desired interface.  An "adapter" class is defined
// that publicly inherits the interface of the abstract class, and
// privately inherits the implementation of the legacy component.  This
// adapter class "maps" or "impedance matches" the new interface to the
// old implementation.

#include <iostream.h>

typedef int Coordinate;
typedef int Dimension;

/////////////////////////// Desired interface ///////////////////////////
class Rectangle {
public:
   virtual void draw() = 0;
};

/////////////////////////// Legacy component ///////////////////////////
class LegacyRectangle {
public:
   LegacyRectangle( Coordinate x1, Coordinate y1,
         Coordinate x2, Coordinate y2 ) {
      x1_ = x1;  y1_ = y1;  x2_ = x2;  y2_ = y2;
      cout << "LegacyRectangle:  create.  (" << x1_ << "," << y1_
         << ") => (" << x2_ << "," << y2_ << ")" << endl; }
   void oldDraw() {
      cout << "LegacyRectangle:  oldDraw.  (" << x1_ << "," << y1_
         << ") => (" << x2_ << "," << y2_ << ")" << endl; }
private:
   Coordinate x1_;
   Coordinate y1_;
   Coordinate x2_;
   Coordinate y2_;
};

/////////////////////////// Adapter wrapper ///////////////////////////
class RectangleAdapter : public Rectangle, private LegacyRectangle {
public:
   RectangleAdapter( Coordinate x, Coordinate y, Dimension w, Dimension h )
         : LegacyRectangle( x, y, x+w, y+h ) {
      cout << "RectangleAdapter: create.  (" << x << "," << y
         << "), width = " << w << ", height = " << h << endl; }
   virtual void draw() {
      cout << "RectangleAdapter: draw." << endl;
      oldDraw(); }
};

main()
{
   Rectangle*  r = new RectangleAdapter( 120, 200, 60, 40 );
   r->draw();
}

// LegacyRectangle:  create.  (120,200) => (180,240)
// RectangleAdapter: create.  (120,200), width = 60, height = 40
// RectangleAdapter: draw.
// LegacyRectangle:  oldDraw.  (120,200) => (180,240)