/*

    Copyright (C) 2016 Apple Inc. All Rights Reserved.

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    An iOS-specific `SKSpriteNode` subclass used to provide the on-screen thumbsticks that enable player control.

*/

import SpriteKit

/// Relay control events though `ThumbStickNodeDelegate`.

protocol ThumbStickNodeDelegate: class {

    /// Called when `touchPad` is moved. Values are normalized between [-1.0, 1.0].

    func thumbStickNode(thumbStickNode: ThumbStickNode, didUpdateXValue xValue: Float, yValue: Float)

    /// Called to indicate when the `touchPad` is initially pressed, and when it is released.

    func thumbStickNode(thumbStickNode: ThumbStickNode, isPressed: Bool)

}

/// Touch representation of a classic analog stick.

class ThumbStickNode: SKSpriteNode {

    // MARK: Properties 

    /// The actual thumb pad that moves with touch.

    var touchPad: SKSpriteNode

    weak var delegate: ThumbStickNodeDelegate?

    /// The center point of this `ThumbStickNode`.

    let center: CGPoint

    /// The distance that `touchPad` can move from the `touchPadAnchorPoint`.

    let trackingDistance: CGFloat

    /// Styling settings for the thumbstick's nodes.

    let normalAlpha: CGFloat = 0.3

    let selectedAlpha: CGFloat = 0.5

    override var alpha: CGFloat {

        didSet {

            touchPad.alpha = alpha

        }

    }

    // MARK: Initialization

    init(size: CGSize) {

        trackingDistance = size.width / 2

        let touchPadLength = size.width / 2.2

        center = CGPoint(x: size.width / 2 - touchPadLength, y: size.height / 2 - touchPadLength)

        let touchPadSize = CGSize(width: touchPadLength, height: touchPadLength)

        let touchPadTexture = SKTexture(imageNamed: "ControlPad")

        // `touchPad` is the inner touch pad that follows the user's thumb.

        touchPad = SKSpriteNode(texture: touchPadTexture, color: UIColor.clearColor(), size: touchPadSize)

        super.init(texture: touchPadTexture, color: UIColor.clearColor(), size: size)

        alpha = normalAlpha

        addChild(touchPad)

    }

    required init?(coder aDecoder: NSCoder) {

        fatalError("init(coder:) has not been implemented")

    }

    // MARK: UIResponder

    override func canBecomeFirstResponder() -> Bool {

        return true

    }

    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {

        super.touchesBegan(touches, withEvent: event)

        // Highlight that the control is being used by adjusting the alpha.

        alpha = selectedAlpha

        // Inform the delegate that the control is being pressed.

        delegate?.thumbStickNode(self, isPressed: true)

    }

    override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {

        super.touchesMoved(touches, withEvent: event)

        // For each touch, calculate the movement of the touchPad.

        for touch in touches {

            let touchLocation = touch.locationInNode(self)

            var dx = touchLocation.x - center.x

            var dy = touchLocation.y - center.y

            // Calculate the distance from the `touchPadAnchorPoint` to the current location.

            let distance = hypot(dx, dy)

            /*

                If the distance is greater than our allowed `trackingDistance`,

                create a unit vector and multiply by max displacement

                (`trackingDistance`).

            */

            if distance > trackingDistance {

                dx = (dx / distance) * trackingDistance

                dy = (dy / distance) * trackingDistance

            }

            // Position the touchPad to match the touch's movement.

            touchPad.position = CGPoint(x: center.x + dx, y: center.y + dy)

            // Normalize the displacements between [-1.0, 1.0].

            let normalizedDx = Float(dx / trackingDistance)

            let normalizedDy = Float(dy / trackingDistance)

            delegate?.thumbStickNode(self, didUpdateXValue: normalizedDx, yValue: normalizedDy)

        }

    }

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

        super.touchesEnded(touches, withEvent: event)

        // If the touches set is empty, return immediately.

        guard !touches.isEmpty else { return }

        resetTouchPad()

   }

    override func touchesCancelled(touches: Set<UITouch>?, withEvent event: UIEvent?) {

        super.touchesCancelled(touches, withEvent: event)

        resetTouchPad()

    }

    /// When touches end, reset the `touchPad` to the center of the control.

    func resetTouchPad() {

        alpha = normalAlpha

        let restoreToCenter = SKAction.moveTo(CGPoint.zero, duration: 0.2)

        touchPad.runAction(restoreToCenter)

        delegate?.thumbStickNode(self, isPressed: false)

        delegate?.thumbStickNode(self, didUpdateXValue: 0, yValue: 0)

    }

}