import UIKit

class ViewController: UIViewController {
    let baseLayer = CAShapeLayer()

    var pinchX: CGFloat = 0
    var pinchY: CGFloat = 0

    var panStart = CGPoint()

    var viewPosition: CGPoint = CGPoint(x:0, y:0) {
        didSet {
            moveToCurrentViewPoint()
        }
    }

    private var chartScaleState: CGFloat = 1
    private var chartScale: CGFloat {
        get {
            return chartScaleState
        }
        set(val) {
            let previousScale = chartScaleState
            chartScaleState = (val) + chartScaleState
            handleScaleAction(scaleAdjust: previousScale / chartScaleState)
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        drawBaseMap()
        viewPosition = CGPoint(x: 0, y: 0)
    }

    @IBAction func handlePinch(_ sender: UIPinchGestureRecognizer) {
        if (sender.state == .changed) {
            let pinchCenter = CGPoint(x: sender.location(in: view).x - view.bounds.midX,
                                      y: sender.location(in: view).y - view.bounds.midY)

            pinchX = pinchCenter.x + (baseLayer.anchorPoint.x * view.bounds.width)
            pinchY = pinchCenter.y + (baseLayer.anchorPoint.y * view.bounds.height)
            chartScale = -((sender.scale - 1) * chartScale)

            sender.scale = 1.0
        }
    }

    @IBAction func panHandle(_ sender: UIPanGestureRecognizer) {
        let location = sender.location(in: self.view)

        if (sender.state == .began) {
            panStart = CGPoint(x: location.x, y: location.y)
        }

        if (sender.state == .changed) {
            let deltaX = panStart.x - location.x
            let deltaY = panStart.y - location.y
            moveItems(deltaX: deltaX, deltaY: deltaY)
            panStart = CGPoint(x: location.x, y: location.y)
        }
    }

    func moveToCurrentViewPoint() {
        baseLayer.anchorPoint = CGPoint(
            x: CGFloat(Double(viewPosition.x) / Double(chartScale)) / baseLayer.bounds.width,
            y: (CGFloat(Double(viewPosition.y) / Double(chartScale)) / baseLayer.bounds.height) * -1
        )
    }

    func drawBaseMap() {
        baseLayer.bounds = CGRect(x: 0, y: 0, width: view.bounds.width, height: view.bounds.height)
        baseLayer.position = CGPoint(x: view.bounds.midX, y: view.bounds.midY)

        baseLayer.anchorPoint = CGPoint(
            x: 0,
            y: 0
        )

        baseLayer.actions = [
            "transform": NSNull(),
            "anchorPoint": NSNull()        ]

        baseLayer.backgroundColor = UIColor.green.cgColor
        baseLayer.strokeColor = UIColor.black.cgColor
        baseLayer.fillColor = UIColor(red: 184/255.0, green: 174/255.0, blue: 87/255.0, alpha: 1.0).cgColor
        baseLayer.lineWidth = 1
        baseLayer.zPosition = -10

        let coolRect = CGRect(x: 0, y: 0, width: 100, height: 100)
        let path = CGMutablePath()
        path.addRect(coolRect)
        self.view.layer.addSublayer(baseLayer)
        baseLayer.path = path
    }

    func handleScaleAction(scaleAdjust: CGFloat) {
        var pathTransform  = CGAffineTransform.identity
        pathTransform = pathTransform.translatedBy(x: pinchX, y: pinchY)
        pathTransform = pathTransform.scaledBy(x: scaleAdjust, y: scaleAdjust)
        pathTransform = pathTransform.translatedBy(x: -(pinchX), y: -(pinchY))

        baseLayer.path = baseLayer.path?.copy(using: &pathTransform)
    }

    public func moveItems(deltaX: CGFloat, deltaY: CGFloat) {
        viewPosition = CGPoint(
            x: Double(viewPosition.y) - (Double(deltaY) * Double(chartScale)),
            y: Double(viewPosition.x) + (Double(deltaX) * Double(chartScale))
        )
    }
}