StretchAnimator.swift

// Custom animation for pull to refresh function as of GMail app
// View figure https://blog.xamarin.com/wp-content/uploads/2013/06/device-swipe-down-refresh.png
// Use combine with https://github.com/jcavar/refresher

import Foundation
import Refresher
import QuartzCore

class BeatAnimator: UIView, PullToRefreshViewDelegate {
  
  private let layerLoader = CAShapeLayer()
  private let layerSeparator = CAShapeLayer()
  private var timer = NSTimer()
  
  override init(frame: CGRect) {
    super.init(frame: frame)
    
    layerLoader.lineWidth = 4
    layerLoader.strokeColor = getRandomColor().CGColor
    layerLoader.strokeEnd = 0
    
    layerSeparator.lineWidth = 1
    layerSeparator.strokeColor = UIColor(red: 0.7, green: 0.7, blue: 0.7, alpha: 1).CGColor
  }
  
  func timerFired(timer: NSTimer) {
    print("timer fired")
    layerLoader.strokeColor = getRandomColor().CGColor
  }
  
  required init(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }
  
  func pullToRefresh(view: PullToRefreshView, progressDidChange progress: CGFloat) {
    layerLoader.strokeStart = 0.5 - progress/2
    layerLoader.strokeEnd = 0.5 + progress/2
  }
  
  func pullToRefresh(view: PullToRefreshView, stateDidChange state: PullToRefreshViewState) {
    
  }
  
  func pullToRefreshAnimationDidEnd(view: PullToRefreshView) {
    layerLoader.removeAllAnimations()
    timer.invalidate()
  }
  
  func getRandomColor() -> UIColor{
    let randomRed:CGFloat = CGFloat(drand48())
    let randomGreen:CGFloat = CGFloat(drand48())
    let randomBlue:CGFloat = CGFloat(drand48())
    return UIColor(red: randomRed, green: randomGreen, blue: randomBlue, alpha: 1.0)
  }
  
  func pullToRefreshAnimationDidStart(view: PullToRefreshView) {
    layerLoader.strokeColor = getRandomColor().CGColor
    
    timer = NSTimer.scheduledTimerWithTimeInterval(0.5, target: self, selector:#selector(timerFired(_:)), userInfo: nil, repeats: true)
    
    let pathAnimationEnd = CABasicAnimation(keyPath: "strokeEnd")
    pathAnimationEnd.duration = 0.5
    pathAnimationEnd.repeatCount = .infinity
    pathAnimationEnd.autoreverses = false
    pathAnimationEnd.fromValue = 0.5
    pathAnimationEnd.toValue = 1
    layerLoader.addAnimation(pathAnimationEnd, forKey: "strokeEndAnimation")
    
    let pathAnimationStart = CABasicAnimation(keyPath: "strokeStart")
    pathAnimationStart.duration = 0.5
    pathAnimationStart.repeatCount = .infinity
    pathAnimationStart.autoreverses = false
    pathAnimationStart.fromValue = 0.5
    pathAnimationStart.toValue = 0
    layerLoader.addAnimation(pathAnimationStart, forKey: "strokeStartAnimation")
  }
  
  override func layoutSubviews() {
    super.layoutSubviews()
    if let superview = superview {
      if layerLoader.superlayer == nil {
        superview.layer.addSublayer(layerLoader)
      }
      if layerSeparator.superlayer == nil {
        superview.layer.addSublayer(layerSeparator)
      }
      
      print("\(superview.frame.height)")
      
      let bezierPathLoader = UIBezierPath()
      bezierPathLoader.moveToPoint(CGPointMake(0, superview.frame.height - 3))
      bezierPathLoader.addLineToPoint(CGPoint(x: superview.frame.width, y: superview.frame.height - 3))
      
      let bezierPathSeparator = UIBezierPath()
      bezierPathSeparator.moveToPoint(CGPointMake(0, superview.frame.height - 1))
      bezierPathSeparator.addLineToPoint(CGPoint(x: superview.frame.width, y: superview.frame.height - 1))
      
      layerLoader.path = bezierPathLoader.CGPath
      layerSeparator.path = bezierPathSeparator.CGPath
    }
  }
}