swift 3.x -> New ChartMarker?

[NoctizJ]

Xcode 8.3.1 force us to use swift 3.x. So I pull in Charts with 3.x version. I have a swift class that uses old ChartMarker after apple's wizard of convert swift version. It seems there is no longer ChartMarker in Swift 3.x. What is the equivalent of that, and could someone help me fix these piece of codes? Thank you in advance!

import Foundation
import UIKit;
import Charts;

open class BalloonMarker: ChartMarker
{
open var bounds = CGRect()
open var dates = NSArray()
open var values = NSArray()
fileprivate var referenceVal = Double()

fileprivate var _size: CGSize = CGSize()
fileprivate var tooltipView: TooltipView

public init(dates: NSArray, values: NSArray, bounds: CGRect, tooltipView: TooltipView)
{
self.tooltipView = tooltipView
_size = tooltipView.frame.size
super.init()

self.dates = dates
self.values = values
self.bounds = bounds
self.referenceVal = values.firstObject as! Double

}

open override var size: CGSize { return _size; }

open override func draw(context: CGContext, point: CGPoint)
{
var rect = CGRect(origin: point, size: self.tooltipView.bounds.size)
let midY = (self.bounds.origin.y + (self.bounds.size.height / 2))
let midX = (self.bounds.origin.x + (self.bounds.size.width / 2))
if (point.y > midY) {
rect.origin.y -= rect.size.height
}

if (point.x > midX) {
  rect.origin.x -= rect.size.width
}
self.tooltipView.frame = rect

}

open override func refreshContent(entry: ChartDataEntry, highlight: ChartHighlight)
{
let date = self.dates[entry.xIndex] as! NSString
let value = self.values[entry.xIndex] as! Double
self.tooltipView.setItemWithDate(date as String, withValue: value, withReferenceValue: self.referenceVal)
}
}

[fogisland]

ChartMarker has been re-written with swift3, try it:
https://github.com/danielgindi/Charts/blob/master/ChartsDemo/Classes/Components/BalloonMarker.swift