Learn-Genie/Learn Genie/Library/LinearProgressBar.swift

//
//  LinearProgressBar.swift
//  Learn Genie
//
//  Created by Suraj Kumar Mandal on 02/09/21.
//

import UIKit

@IBDesignable
public class DSGradientProgressView: UIView, CAAnimationDelegate {
    
    @IBInspectable public var barColor: UIColor = UIColor(hue: (29.0/360.0), saturation: 1.0, brightness: 1.0, alpha: 1.0) {
        didSet {
            initialize()
        }
    }
    
    private let serialIncrementQueue = DispatchQueue(label: "com.dholstudio.DSGradientProgressView.serialIncrementQueue")
    
    private var numberOfOperations: Int = 0
    
    override public class var layerClass: AnyClass {
        get {
            return CAGradientLayer.self
        }
    }
    
    // https://theswiftdev.com/2015/08/05/swift-init-patterns/
    
    override public init(frame: CGRect) {
        super.init(frame: frame)
        
        self.initialize()
    }
    
    required public init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)!
        
        self.initialize()
    }
    
    override public func awakeFromNib() {
        super.awakeFromNib()
        
        self.initialize()
    }
    
    private func initialize() {
        
        let layer = self.layer as! CAGradientLayer
        
        // Use a horizontal gradient
        layer.startPoint = CGPoint(x: 0.0, y: 0.5)
        layer.endPoint = CGPoint(x: 1.0, y: 0.5)
        
        var colors: [CGColor] = []
        
        // http://stackoverflow.com/a/39126332/2607823
        // http://bjmiller.me/post/137624096422/on-c-style-for-loops-removed-from-swift-3
        // stride syntax changed from the blog's syntax
        
        /*
         
         // ==== Blue gradient with changing hues ====
         for hue in stride(from: 190, through: 230, by: 2) {
         let color = UIColor(hue: CGFloat(1.0 * Double(hue) / 360.0),
         saturation: 1.0,
         brightness: 1.0,
         alpha: 1.0)
         
         colors.append(color.cgColor)
         }
         
         // can be done with stride with -2 too. but just to explore another way..
         
         for hue in (190...230).reversed() where hue % 2 == 0 {
         let color = UIColor(hue: CGFloat(1.0 * Double(hue) / 360.0),
         saturation: 1.0,
         brightness: 1.0,
         alpha: 1.0)
         
         colors.append(color.cgColor)
         }
         */
        
        // ==== Constant hue with changing alpha ====
        
        /*
         for alpha in stride(from: 0, through: 40, by: 2) {
         
         let color = UIColor(hue: CGFloat(1.0 * Double(hue) / 360.0),
         saturation: 1.0,
         brightness: 1.0,
         alpha: CGFloat(1.0 * Double(alpha)/100.0))
         
         barColor.withAlphaComponent(CGFloat(alpha))
         
         colors.append(color.cgColor)
         }
         */
        
        // === constant color from storyboard or default with changing alpha ===
        for alpha in stride(from: 0, through: 40, by: 2) {
            
            let color = barColor.withAlphaComponent(CGFloat(Double(alpha)/100.0))
            
            colors.append(color.cgColor)
        }
        
        for alpha in stride(from: 40, through: 90, by: 10) {
            
            let color = barColor.withAlphaComponent(CGFloat(Double(alpha)/100.0))
            
            colors.append(color.cgColor)
        }
        
        for alpha in stride(from: 90, through: 100, by: 10) {
            
            let color = barColor.withAlphaComponent(CGFloat(Double(alpha)/100.0))
            
            colors.append(color.cgColor)
            colors.append(color.cgColor) // adding twice
        }
        
        for alpha in stride(from: 100, through: 0, by: -20) {
            
            let color = barColor.withAlphaComponent(CGFloat(Double(alpha)/100.0))
            
            colors.append(color.cgColor)
        }
        
        layer.colors = colors
    }
    
    private func performAnimation() {
        
        // Move the last color in the array to the front
        // shifting all the other colors.
        let layer = self.layer as! CAGradientLayer
        
        guard let color = layer.colors?.popLast() else {
            print("FATAL ERR: GradientProgressView : Layer should contain colors!")
            return
        }
        
        layer.colors?.insert(color, at: 0)
        
        let shiftedColors = layer.colors!
        
        let animation = CABasicAnimation(keyPath: "colors")
        animation.toValue = shiftedColors
        animation.duration = 0.03
        animation.isRemovedOnCompletion = true
        animation.fillMode = CAMediaTimingFillMode.forwards
        animation.delegate = self
        layer.add(animation, forKey: "animateGradient")
    }
    
    public func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
        
        // TODO: Make reads on serial queue too?
        
        if flag && numberOfOperations > 0 {
            
            performAnimation()
        }
        else {
            self.isHidden = true
        }
    }
    
    public func startProgress() {
        serialIncrementQueue.sync {
            numberOfOperations += 1
        }
        self.isHidden = false
        
        if numberOfOperations == 1 { // rest will be called from animationDidStop
            performAnimation()
        }
    }
    
    public func stopProgress() {
        
        if numberOfOperations == 0 {
            return
        }
        
        serialIncrementQueue.sync {
            numberOfOperations -= 1
        }
    }
    
    /*
     // Only override draw() if you perform custom drawing.
     // An empty implementation adversely affects performance during animation.
     override func draw(_ rect: CGRect) {
     // Drawing code
     }
     */
    
}