Joystick.swift

import SpriteKit

class Joystick: SKNode {
    private let substrate: SKSpriteNode
    private let stick: SKSpriteNode

    var resetAnimationDuration: NSTimeInterval = 0.3

    var velocity: CGPoint = .zero
    var angularVelocity: CGFloat = 0
    
    override var zPosition: CGFloat {
        get {
            return super.zPosition
        }
        set {
            super.zPosition = newValue
            recalculateNodesZPosition()
        }
    }

    private var anchorPoint: CGPoint {
        return CGPointMake(0, 0)
    }

    var expectedSize: CGSize {
        return CGSizeMake(substrate.size.width + substrate.size.width, substrate.size.height + substrate.size.height)
    }

    override init(substrateSprite: SKSpriteNode, stickSprite: SKSpriteNode) {
        substrate = substrateSprite
        stick = stickSprite
        super.init()
        setup()
    }
    
    private func setup() {
        userInteractionEnabled = true
        setupSubtrate()
        setupStick(substrate.position)
        recalculateNodesZPosition()
    }

    private func setupSubtrate() {
        substrate.xScale = 0.3
        substrate.yScale = 0.3
        substrate.zPosition = self.zPosition
        addChild(substrate)
    }

    private func setupStick(position: CGPoint) {
        stick.xScale = 0.22
        stick.yScale = 0.22
        stick.zPosition = substrate.zPosition + 1
        moveStick(position)
        addChild(stick)
    }
    
    private func recalculateNodesZPosition() {
        substrate.zPosition = zPosition
        stick.zPosition = substrate.zPosition + 1
    }
    
    private func moveStick(position: CGPoint) {
        stick.position = position
    }

    private func resetStick() {
        let animation = SKAction.moveTo(anchorPoint, duration: resetAnimationDuration)
        animation.timingMode = SKActionTimingMode.EaseOut
        stick.runAction(animation)
    }
    
    private func resetVelocity() {
        velocity = .zero
        angularVelocity = 0
    }

    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        if let touch = touches.first where substrate == nodeAtPoint(touch.locationInNode(self)) {
            let position = touch.locationInNode(self)
            moveStick(position)
        }
    }

    override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
        touches.forEach { t in
            let location = t.locationInNode(self)
            if sqrtf(powf((Float(location.x) - Float(stick.position.x)), 2) + powf((Float(location.y) - Float(stick.position.y)), 2)) < Float(stick.size.width) {
                moveStick(calculateStickPosition(forTouchPoint: location))
            }
            self.velocity = CGPointMake(((stick.position.x - anchorPoint.x)), ((stick.position.y - anchorPoint.y)))
            self.angularVelocity = -atan2(stick.position.x - anchorPoint.x, stick.position.y - anchorPoint.y)
        }
    }

    private func calculateStickPosition(forTouchPoint touchPoint: CGPoint) -> CGPoint {
        if sqrtf(powf((Float(touchPoint.x) - Float(anchorPoint.x)), 2) + powf((Float(touchPoint.y) - Float(anchorPoint.y)), 2)) <= Float(stick.size.width) {
            let moveDifference: CGPoint = CGPointMake(touchPoint.x - anchorPoint.x, touchPoint.y - anchorPoint.y)
            return CGPointMake(anchorPoint.x + moveDifference.x, anchorPoint.y + moveDifference.y)
        } else {
            let vX: Double = Double(touchPoint.x) - Double(anchorPoint.x)
            let vY: Double = Double(touchPoint.y) - Double(anchorPoint.y)
            let magV: Double = sqrt(vX*vX + vY*vY)
            let aX: Double = Double(anchorPoint.x) + vX / magV * Double(stick.size.width)
            let aY: Double = Double(anchorPoint.y) + vY / magV * Double(stick.size.width)
            return CGPointMake(CGFloat(aX), CGFloat(aY))
        }
    }
    
    override func touchesCancelled(touches: Set<UITouch>?, withEvent event: UIEvent?) {
        resetVelocity()
        resetStick()
    }

    override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
        resetVelocity()
        resetStick()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}