class Balloon : Movable {

    static val sideSpeed = 20

    // AirBalloon sets this to SOUTH.
    var direction = NORTH

    override fun begin() {
        super.begin()
        speed = speed / 2
    }

    override fun myTurn() {
        val north = lookNorth()
        if (north.squashable( NORTH )) {
            moveNorth()
        } else {
            if ( north.rounded( SOUTH_WEST ) && canRoll(-1) ) {
                roll( -1 )
            } else if ( north.rounded( SOUTH_EAST ) && canRoll(1) ) {
                roll( 1 )
            }
        }
    }

    fun roll( dx : int) {
        moveDelta(dx, 0, sideSpeed )
    }

    fun canRoll( dx : int ) : boolean {
        val side = lookDelta( dx, 0, sideSpeed )
        if (! ( side.isEmpty() ) ) {
            return false
        }

        val above = lookDelta( dx, if (direction == NORTH) 1 else -1 )
        return above.squashable( direction )
    }

    override fun canPush( direction : int, speed : int, strength : int ) : boolean {
        if ( isMoving() ) return false
        if ( direction == this.direction) return false

        val next = look( direction, speed )
        if ( next.squashable( direction ) ) {
            return true
        }
        if (next == this) {
            println( "Eek! Ballon would have caused stack overflow!" )
            return false
        }
        return next.canPush( direction, speed, 0 )
    }

    override fun rounded( direction : int ) = true

    override fun copyable() = true
}