/*
 *  This program implements a 2D bouncing ball in the 2 x 2 square box
 *  with center at the origin.
 *
 *  Assume your CLASSPATH environment contains the path to stdlib.jar.
 *
 *  Compilation:  kotlinc -cp $CLASSPATH BouncingBall.kt
 *  Execution:    kotlin -cp $CLASSPATH BouncingBallKt
 *  Dependencies: StdDraw and StdAudio
 *                http://www.cs.princeton.edu/introcs/15inout/laser.wav
 *                http://www.cs.princeton.edu/introcs/15inout/pop.wav
 *                http://www.cs.princeton.edu/introcs/15inout/earth.gif
 *                http://introcs.cs.princeton.edu/java/stdlib/stdlib.jar
 */

/* MAX_R is the maximum x- and y-coordinates of the bounding box.
   We'll set the minimum to -MAX_R. */
const val MAX_R = 1.0
// The following three numbers are gotten by trial and error.
const val MIN_V = 0.005  // minimum velocity
const val MAX_V = 0.015  // maximum velocity
const val BALL_RADIUS = 0.03  // a hack since "earth.gif" is in pixels

fun main(args: Array<String>) {
    // set the scale of the coordinate system
    StdDraw.setScale(-MAX_R, MAX_R)

    // range of x-coordinate and y-coordinate of position
    val rRange = -MAX_R..MAX_R

    StdDraw.enableDoubleBuffering()

    var randGen = java.util.concurrent.ThreadLocalRandom.current()

    // pick a random starting position for the ball
    var rx = randGen.nextDouble(-MAX_R, MAX_R) // x-coordinate of position
    var ry = randGen.nextDouble(-MAX_R, MAX_R) // y-coordinate of position

    // pick a random starting velocity for the ball
    var vx = randGen.nextDouble(MIN_V, MAX_V) // x-coordinate of velocity
    var vy = randGen.nextDouble(MIN_V, MAX_V) // y-coordinate of velocity

    // main animation loop
    while (true) { 

        // find the new position of the ball
        if (((rx + vx) + BALL_RADIUS) !in rRange) {
            vx = -vx
            StdAudio.play("laser.wav")
        }
        if (((ry + vy) + BALL_RADIUS) !in rRange) {
            vy = -vy
            StdAudio.play("pop.wav")
        }
        rx += vx
        ry += vy

        // clear the display buffer and draw the ball
        StdDraw.clear()
        StdDraw.picture(rx, ry, "earth.gif")

        // show the display buffer
        StdDraw.show()

        // show the buffer long enough to create animation in the viewer's mind
        StdDraw.pause(20)
    }
}