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

/**
   The class represents Swing based graphics device.
 */
class SwingGraphics implements TGraphics {
    private char[][] display;
    private int width, height;
    private SwingCanvas canvas;
    private Container pane;
    private JFrame frame;
    private Graphics g;
    
    /**
       Construct a graphics object for a console with the specified 
       dimensions.
       @param width - the width of the drawable area in characters.
       @param height - the height of the drawable area in characters.
     */
    SwingGraphics(int width, int height) {
        frame = new JFrame();
        pane = frame.getContentPane();
        canvas = new SwingCanvas(width, height);
        pane.setBackground(Color.white);
        pane.add(canvas);
        this.width = width;
        this.height = height;
        frame.pack();
        frame.show();
        g = canvas.getGraphics();
        getDrawingGraphics();
    }
    /**
       Draw a line from (x1, y1) to (x2, y2).
       @param x1 - x coordinate of first point.
       @param y1 - y coordinate of first point.
       @param x2 - x coordinate of second point.
       @param y2 - y coordinate of second point.
     */
    public void drawLine(int x1, int y1, int x2, int y2) {
      offscreenGraphics.drawLine(x1, y1, x2, y2);
    }
    /**
       Copy what has been drawn onto the display to the console.
     */
    public void render() {
        g.drawImage(offscreenImage,0,0,width,height,null);
        offscreenGraphics.setColor(Color.white);
        offscreenGraphics.fillRect(0,0,width, height); // mimic a device that forgets
        offscreenGraphics.setColor(Color.black);
    }

    /**
       Clear the display.
     */
    public void clear() {
        Color save = g.getColor();
        g.setColor(Color.white);
        g.fillRect(0,0,width, height);
        g.setColor(save);
    }
    /**
       Make the offscreen image if one doesn't exist.
       This must be called AFTER the canvas has been created an initially displayed.
    */
    private void getDrawingGraphics() {
        if (offscreenGraphics == null) {
            offscreenImage = canvas.createImage(width, height);
            offscreenGraphics = offscreenImage.getGraphics();
        }
    }
    private Image offscreenImage;
    private Graphics offscreenGraphics;

}