//
// program to demonstrate a little of the functionality needed for a drawing
// program:  controlling what is drawn on screen, responding to mouse and
// keyboard input
//
// click and drag to draw a rectangle, type 'c' to clear
//
import scala.swing._
import scala.swing.event._
import java.awt.Color
import java.awt.Graphics2D

// point where user pressed mouse button (-1 for none)
// (Point is in scala.swing)
// (we probably should use "null" for none but we don't know about that yet)
var startPoint = new Point(-1, -1)
// point where user released mouse button (-1 for none)
var endPoint = new Point(-1, -1)
// current "drag" point (-1 for none)
var dragPoint = new Point(-1, -1)

// get rectangle defined by two points
// (Rectangle is in scala.swing)
def pointsToRectangle(p1 : Point, p2 : Point) : Rectangle = {
  val left = p1.x min p2.x
  val top = p1.y min p2.y
  val w = math.abs(p1.x - p2.x)
  val h = math.abs(p1.y - p2.y)
  new Rectangle(left, top, w, h)
}

// panel for drawing
val drawingPanel = new Panel { 
  override def paint(g : Graphics2D) {
    g.setPaint(Color.WHITE)
    // clear background
    g.fill(new Rectangle(0,0,size.width,size.height))

    g.setPaint(Color.GREEN)
    // "fill" completed rectangle
    if ((startPoint.x != -1) && (endPoint.x != -1)) {
      g.fill(pointsToRectangle(startPoint, endPoint))
    }
    // draw outline of rectangle in progress
    if ((startPoint.x != -1) && (dragPoint.x != -1)) {
      g.draw(pointsToRectangle(startPoint, dragPoint))
    }
  }
  listenTo(mouse.clicks,mouse.moves,keys)
  reactions += {
    case e:MousePressed =>
      requestFocus() // only needed because we have keyboard input too
      startPoint = e.point
      endPoint = new Point(-1, -1)
      dragPoint = new Point(-1, -1)
      repaint()
    case e:MouseReleased =>
      requestFocus() // only needed because we have keyboard input too
      endPoint = e.point
      dragPoint = new Point(-1, -1)
      repaint()
    case e:MouseDragged =>
      requestFocus() // only needed because we have keyboard input too
      dragPoint = e.point
      repaint()
    case e:KeyTyped =>
      requestFocus() // only needed because we have keyboard input too
      if (e.char == 'c') {
        startPoint = new Point(-1, -1)
        endPoint = new Point(-1, -1)
        dragPoint = new Point(-1, -1)
      }
      repaint()
  }
}

// main layout
val frame = new MainFrame {
  title = "Drawing Program Prototype"
  contents = new BorderPanel {
    layout += (drawingPanel -> BorderPanel.Position.Center)
  }
  size = new Dimension(400,400)
}

// start up
frame.visible = true