GearRefreshControl.swift

//
//  GearRefreshControl.swift
//  GearRefreshControl
//
//  Created by Andrea Mazzini on 04/04/15.
//  Copyright (c) 2015 Fancy Pixel. All rights reserved.
//

import UIKit

/**
 Defines a custom `UIRefreshControl` with spinning gears.
 */
open class GearRefreshControl: UIRefreshControl {
  
  /**
   Tells if the control is currently animating
   */
  open fileprivate(set) var isRefreshControlAnimating = false
  
  /**
   Tint color for the control. Set the color of the main gear, the other ones are computed automatically
   */
  dynamic open var gearTintColor: UIColor? {
    get { return self.centerGear.tintColor }
    set {
      centerGear.tintColor = newValue
      topGear.tintColor = newValue?.darkerColor(0.85)
      rightGear.tintColor = newValue?.darkerColor(0.75)
      bottomGear.tintColor = newValue?.darkerColor(0.85)
      leftGear.tintColor = newValue?.darkerColor(0.75)
      refreshContainerView.backgroundColor = newValue?.darkerColor(0.5)
    }
  }
  
  fileprivate var refreshContainerView: UIView!
  fileprivate var overlayView: UIView!
  fileprivate var shadowView: ShadowView = {
    let view = ShadowView()
    view.shadowPercentage = 0.2
    return view
  }()
  fileprivate var centerGear: MainGear = {
    let view = MainGear()
    view.frame = CGRect(x: 0, y: 0, width: 48, height: 48)
    view.backgroundColor = .clear
    return view
  }()
  fileprivate var topGear: BigGear = { // cue Jessica from the Allman brothers
    let view = BigGear()
    view.frame = CGRect(x: 0, y: 0, width: 92, height: 92)
    view.backgroundColor = .clear
    return view
  }()
  fileprivate var rightGear: BigGear = {
    let view = BigGear()
    view.frame = CGRect(x: 0, y: 0, width: 92, height: 92)
    view.backgroundColor = .clear
    return view
  }()
  fileprivate var bottomGear: BigGear = {
    let view = BigGear()
    view.frame = CGRect(x: 0, y: 0, width: 88, height: 88)
    view.backgroundColor = .clear
    return view
  }()
  fileprivate var leftGear: BigGear = {
    let view = BigGear()
    view.frame = CGRect(x: 0, y: 0, width: 92, height: 92)
    view.backgroundColor = .clear
    return view
  }()
  
  /**
   Use init(frame:) instead
   */
  required override public init() {
    fatalError("use init(frame:) instead")
  }
  
  /**
   Use init(frame:) instead
   */
  required public init(coder aDecoder: NSCoder) {
    fatalError("use init(frame:) instead")
  }
  
  /**
   Initialize the gear refresh control
   */
  required override public init(frame: CGRect) {
    super.init()
    bounds.size.width = frame.size.width
    setupRefreshControl()
  }
  
  /**
   Scroll update
   
   Updates the scroll status of the gears.
   
   - Parameter scrollView: The scrollview being observed
   */
  open func scrollViewDidScroll(_ scrollView: UIScrollView) {
    var refreshBounds = self.bounds;
    
    // Distance the table has been pulled
    let pullDistance = max(0.0, -self.frame.origin.y);
    let pullRatio = min(max(pullDistance, 0.0), 140.0) / 140.0;
    
    overlayView.alpha = 1 - pullRatio
    shadowView.frame = self.bounds
    
    centerGear.center = CGPoint(x: self.refreshContainerView.frame.midX, y: pullDistance / 2)
    topGear.center = CGPoint(x: self.refreshContainerView.frame.midX + 48, y: pullDistance / 2 - 49)
    rightGear.center = CGPoint(x: self.refreshContainerView.frame.midX + 120, y: pullDistance / 2)
    bottomGear.center = CGPoint(x: self.refreshContainerView.frame.midX - 47, y: pullDistance / 2 + 46)
    leftGear.center = CGPoint(x: self.refreshContainerView.frame.midX - 105, y: pullDistance / 2 - 17)
    
    refreshBounds.size.height = pullDistance;
    
    [self.refreshContainerView, self.overlayView].forEach { $0.frame = refreshBounds }
    
    // Don't rotate the gears if the refresh animation is playing
    if !isRefreshing && !isRefreshControlAnimating {
      centerGear.transform = CGAffineTransform(rotationAngle: (.pi / 2) * pullRatio)
      topGear.transform = CGAffineTransform(rotationAngle: 0.025 - 0.9 * pullRatio)
      rightGear.transform = CGAffineTransform(rotationAngle: -0.03 + 0.9 * pullRatio)
      bottomGear.transform = CGAffineTransform(rotationAngle: 0.025 - 0.9 * pullRatio)
      leftGear.transform = CGAffineTransform(rotationAngle: 0.025 + 0.9 * pullRatio)
    }
    
    // If we're refreshing and the animation is not playing, then play the animation
    if isRefreshing && !isRefreshControlAnimating {
      animateRefreshView()
    }
  }
  
}

private extension GearRefreshControl {
  func setupRefreshControl() {
    
    refreshContainerView = UIView(frame: self.bounds)
    
    overlayView = UIView(frame: self.bounds)
    overlayView.backgroundColor = UIColor.black.withAlphaComponent(0.3)
    
    shadowView.frame = self.bounds
    
    gearTintColor = UIColor(red:0.36, green:0.52, blue:0.92, alpha:1)
    
    centerGear.center = CGPoint(x: self.refreshContainerView.frame.midX, y: self.refreshContainerView.frame.midY)
    topGear.center = CGPoint(x: self.refreshContainerView.frame.midX + 48, y: self.refreshContainerView.frame.midY - 49)
    rightGear.center = CGPoint(x: self.refreshContainerView.frame.midX + 120, y: self.refreshContainerView.frame.midY)
    bottomGear.center = CGPoint(x: self.refreshContainerView.frame.midX - 48, y: self.refreshContainerView.frame.midY + 42)
    leftGear.center = CGPoint(x: self.refreshContainerView.frame.midX - 110, y: self.refreshContainerView.frame.midY - 18)
    
    [topGear, rightGear, bottomGear, leftGear, centerGear, shadowView, overlayView].forEach { self.refreshContainerView.addSubview($0) }
    
    refreshContainerView.clipsToBounds = true
    tintColor = UIColor.clear
    
    addSubview(self.refreshContainerView)
  }
  
  func animateRefreshView() {
    isRefreshControlAnimating = true
    
    UIView.animate(withDuration: 0.3, delay: 0, options: .curveLinear, animations: {
      self.centerGear.transform = self.centerGear.transform.rotated(by: .pi / 2)
      self.topGear.transform = self.topGear.transform.rotated(by: -(.pi / 2))
      self.rightGear.transform = self.rightGear.transform.rotated(by: .pi / 2)
      self.bottomGear.transform = self.bottomGear.transform.rotated(by: -(.pi / 2))
      self.leftGear.transform = self.leftGear.transform.rotated(by: .pi / 2)
    }, completion: { finished in
      // If still refreshing, keep spinning
      if self.isRefreshing {
        self.animateRefreshView()
      } else {
        self.isRefreshControlAnimating = false
      }
    })
  }
}

private class ShadowView: UIView {
  var gradient: CAGradientLayer!
  var shadowPercentage = 0.0
  
  override func layoutSubviews() {
    clipsToBounds = true
    var frame = self.frame
    let offset = frame.size.height * CGFloat(shadowPercentage)
    frame.size.height = offset
    if gradient == nil {
      gradient = CAGradientLayer()
      gradient.frame = frame
      gradient.colors = [
        UIColor.black.withAlphaComponent(0.6).cgColor,
        UIColor.black.withAlphaComponent(0.15).cgColor,
        UIColor.clear.cgColor]
      self.layer.insertSublayer(self.gradient, at: 0)
    } else {
      gradient.frame = frame
    }
  }
}

private extension UIColor {
  func darkerColor(_ delta: CGFloat) -> UIColor {
    var h = CGFloat(0)
    var s = CGFloat(0)
    var b = CGFloat(0)
    var a = CGFloat(0)
    self.getHue(&h, saturation: &s, brightness: &b, alpha: &a)
    return UIColor(hue: h, saturation: s, brightness: b * delta, alpha: a)
  }
}