import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

/**
 *  A very simple drawing program that lets the user add shapes to a drawing
 *  area and drag them around.  An abstract Shape class is used to represent
 *  shapes in general, with subclasses to represent particular kinds of shape.
 *  (These are implemented as nested classes inside the main class.)  This
 *  program is an illustration of class hierarchy, inheritance, polymorphism,
 *  and abstract classes.  (Note that this program will fail if you add more
 *  than 500 shapes, since it uses an array of length 500 to store the shapes.)
 */
public class ShapeDraw extends JPanel {
    
    /**
     * A main routine that allows this class to be run as an application.
     * It simply opens a window displaying a ShapeDraw panel.
     */
    public static void main(String[] args) {
        JFrame window = new JFrame("Really Simple ShapeDraw");
        window.setContentPane( new ShapeDraw() );
        window.setSize(500,400);
        
        window.setLocation(150,100);
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setVisible(true);
    }
    

    /**
     * Set up the GUI, with a drawing area plus a row of controls below the
     * drawing area.  The controls include three buttons which are used
     * to add shapes to the drawing area and a menu that is used to select
     * the color of the shape when it is created.  The constructor also
     * sets up listeners to handle events from the controls.
     */
    public ShapeDraw() {  

        setBackground(Color.LIGHT_GRAY);

        DrawingArea canvas = new DrawingArea();  // create the canvas

        colorChoice = new JComboBox<String>();  // color choice menu
        colorChoice.addItem("Red");
        colorChoice.addItem("Green");
        colorChoice.addItem("Blue");
        colorChoice.addItem("Cyan");
        colorChoice.addItem("Magenta");
        colorChoice.addItem("Yellow");
        colorChoice.addItem("Black");
        colorChoice.addItem("White");
        colorChoice.addActionListener(canvas);

        JButton rectButton = new JButton("Rect");    // buttons for adding shapes
        rectButton.addActionListener(canvas);

        JButton ovalButton = new JButton("Oval");
        ovalButton.addActionListener(canvas);

        JButton roundRectButton = new JButton("RoundRect");
        roundRectButton.addActionListener(canvas);

        JPanel bottom = new JPanel();   // a Panel to hold the control buttons
        bottom.setLayout(new GridLayout(1,4,3,3));
        bottom.add(rectButton);
        bottom.add(ovalButton);
        bottom.add(roundRectButton);
        bottom.add(colorChoice);

        setLayout(new BorderLayout(3,3));
        add(canvas, BorderLayout.CENTER);              // add canvas and controls to the panel
        add(bottom, BorderLayout.SOUTH);

    } // end constructor

    JComboBox<String> colorChoice;  // The color selection menu

    //---- Nested class definitions ---
    //
    // The remainder of the ShapeDraw class consists of static nested class definitions.
    // These are just like regular classes, except that they are defined inside
    // another class (and hence have full names, when used outside this class, such
    // as ShapeDraw.ShapeCanvas).

    /**
     * This nested class defines the drawing area.
     */
    class DrawingArea extends JPanel
                     implements ActionListener, MouseListener, MouseMotionListener {

        // This class represents a "canvas" that can display colored shapes and
        // let the user drag them around.  It uses an off-screen images to 
        // make the dragging look as smooth as possible.

        Shape[] shapes = new Shape[500]; // holds a list of up to 500 shapes
        int shapeCount = 0;  // the actual number of shapes
        Color currentColor = Color.RED;  // current color; when a shape is created, this is its color


        DrawingArea() {
               // Constructor: set background color to white set up listeners to respond to mouse actions
            setBackground(Color.WHITE);
            addMouseListener(this);
            addMouseMotionListener(this);
        }   

        public void paintComponent(Graphics g) {
               // In the paint method, all the shapes in ArrayList are
               // copied onto the canvas.
            g.setColor(Color.WHITE);
            g.fillRect(0,0,getSize().width,getSize().height);
            for (int i = 0; i < shapeCount; i++) {
                Shape s = shapes[i];
                s.draw(g);
            }
            g.setColor(Color.BLACK);  // draw a black border around the edge of the drawing area
            g.drawRect(0,0,getWidth()-1,getHeight()-1);
        }   

        public void actionPerformed(ActionEvent evt) {
               // Called to respond to action events.  The three shape-adding
               // buttons have been set up to send action events to this canvas.
               // Respond by adding the appropriate shape to the canvas.
            if (evt.getSource() == colorChoice) {
                switch ( colorChoice.getSelectedIndex() ) {
                case 0: currentColor = Color.RED;     break;
                case 1: currentColor = Color.GREEN;   break;
                case 2: currentColor = Color.BLUE;    break;
                case 3: currentColor = Color.CYAN;    break;
                case 4: currentColor = Color.MAGENTA; break;
                case 5: currentColor = Color.YELLOW;  break;
                case 6: currentColor = Color.BLACK;   break;
                case 7: currentColor = Color.WHITE;   break;
                }
            }
            else {
                String command = evt.getActionCommand();
                if (command.equals("Rect"))
                    addShape(new RectShape());
                else if (command.equals("Oval"))
                    addShape(new OvalShape());
                else if (command.equals("RoundRect"))
                    addShape(new RoundRectShape());
            }
        }

        void addShape(Shape shape) {
                // Add the shape to the canvas, and set its size/position and color.
                // The shape is added at the top-left corner, with size 80-by-50.
                // Then redraw the canvas to show the newly added shape.
            shape.setColor(currentColor);
            shape.reshape(3,3,80,50);
            shapes[shapeCount] = shape;
            shapeCount++;
            repaint();
        }


        // -------------------- This rest of this class implements dragging ----------------------

        Shape shapeBeingDragged = null;  // This is null unless a shape is being dragged.
                                         // A non-null value is used as a signal that dragging
                                         // is in progress, as well as indicating which shape
                                         // is being dragged.

        int prevDragX;  // During dragging, these record the x and y coordinates of the
        int prevDragY;  //    previous position of the mouse.

        public void mousePressed(MouseEvent evt) {
                // User has pressed the mouse.  Find the shape that the user has clicked on, if
                // any.  If there is a shape at the position when the mouse was clicked, then
                // start dragging it.  If the user was holding down the shift key, then bring
                // the dragged shape to the front, in front of all the other shapes.
            int x = evt.getX();  // x-coordinate of point where mouse was clicked
            int y = evt.getY();  // y-coordinate of point 
            for ( int i = shapeCount - 1; i >= 0; i-- ) {  // check shapes from front to back
                Shape s = shapes[i];
                if (s.containsPoint(x,y)) {
                    shapeBeingDragged = s;
                    prevDragX = x;
                    prevDragY = y;
                    if (evt.isShiftDown()) { // s should be moved on top of all the other shapes
                        for (int j = i; j < shapeCount-1; j++) {
                                // move the shapes following s down in the list
                            shapes[j] = shapes[j+1];
                        }
                        shapes[shapeCount-1] = s;  // put s at the end of the list
                        repaint();  // repaint canvas to show s in front of other shapes
                    }
                    return;
                }
            }
        }

        public void mouseDragged(MouseEvent evt) {
                // User has moved the mouse.  Move the dragged shape by the same amount.
            int x = evt.getX();
            int y = evt.getY();
            if (shapeBeingDragged != null) {
                shapeBeingDragged.moveBy(x - prevDragX, y - prevDragY);
                prevDragX = x;
                prevDragY = y;
                repaint();      // redraw canvas to show shape in new position
            }
        }

        public void mouseReleased(MouseEvent evt) {
                // User has released the mouse.  Move the dragged shape, then set
                // shapeBeingDragged to null to indicate that dragging is over.
            int x = evt.getX();
            int y = evt.getY();
            if (shapeBeingDragged != null) {
                shapeBeingDragged.moveBy(x - prevDragX, y - prevDragY);
                shapeBeingDragged = null;
                repaint();
            }
        }

        public void mouseEntered(MouseEvent evt) { }   // Other methods required for MouseListener and 
        public void mouseExited(MouseEvent evt) { }    //              MouseMotionListener interfaces.
        public void mouseMoved(MouseEvent evt) { }
        public void mouseClicked(MouseEvent evt) { }

    }  // end class DrawingArea

    

    // ------- Nested class definitions for the abstract Shape class and three -----
    // -------------------- concrete subclasses of Shape. --------------------------


    static abstract class Shape {

            // A class representing shapes that can be displayed on a ShapeCanvas.
            // The subclasses of this class represent particular types of shapes.
            // When a shape is first constructed, it has height and width zero
            // and a default color of white.

        int left, top;      // Position of top left corner of rectangle that bounds this shape.
        int width, height;  // Size of the bounding rectangle.
        Color color = Color.white;  // Color of this shape.

        void reshape(int left, int top, int width, int height) {
                // Set the position and size of this shape.
            this.left = left;
            this.top = top;
            this.width = width;
            this.height = height;
        }

        void moveBy(int dx, int dy) {
                // Move the shape by dx pixels horizontally and dy pixels vertically
                // (by changing the position of the top-left corner of the shape).
            left += dx;
            top += dy;
        }

        void setColor(Color color) {
                // Set the color of this shape
            this.color = color;
        }

        boolean containsPoint(int x, int y) {
                // Check whether the shape contains the point (x,y).
                // By default, this just checks whether (x,y) is inside the
                // rectangle that bounds the shape.  This method should be
                // overridden by a subclass if the default behavior is not
                // appropriate for the subclass.
            if (x >= left && x < left+width && y >= top && y < top+height)
                return true;
            else
                return false;
        }

        abstract void draw(Graphics g);  
            // Draw the shape in the graphics context g.
            // This must be overriden in any concrete subclass.

    }  // end of class Shape



    static class RectShape extends Shape {
            // This class represents rectangle shapes.
        void draw(Graphics g) {
            g.setColor(color);
            g.fillRect(left,top,width,height);
            g.setColor(Color.black);
            g.drawRect(left,top,width,height);
        }
    }


    static class OvalShape extends Shape {
            // This class represents oval shapes.
        void draw(Graphics g) {
            g.setColor(color);
            g.fillOval(left,top,width,height);
            g.setColor(Color.black);
            g.drawOval(left,top,width,height);
        }
        boolean containsPoint(int x, int y) {
                // Check whether (x,y) is inside this oval, using the
                // mathematical equation of an ellipse.  This replaces the
                // definition of containsPoint that was inherited from the
                 // Shape class.
            double rx = width/2.0;   // horizontal radius of ellipse
            double ry = height/2.0;  // vertical radius of ellipse 
            double cx = left + rx;   // x-coord of center of ellipse
            double cy = top + ry;    // y-coord of center of ellipse
            if ( (ry*(x-cx))*(ry*(x-cx)) + (rx*(y-cy))*(rx*(y-cy)) <= rx*rx*ry*ry )
                return true;
            else
                return false;
        }
    }


    static class RoundRectShape extends Shape {
            // This class represents rectangle shapes with rounded corners.
            // (Note that it uses the inherited version of the 
            // containsPoint(x,y) method, even though that is not perfectly
            // accurate when (x,y) is near one of the corners.)
        void draw(Graphics g) {
            g.setColor(color);
            g.fillRoundRect(left,top,width,height,width/3,height/3);
            g.setColor(Color.black);
            g.drawRoundRect(left,top,width,height,width/3,height/3);
        }
    }


}  // end class ShapeDraw