CircularProgressView.swift

import UIKit

@IBDesignable class CircularProgressView: UIView {
    
    // MARK: - Initialization
    
    public override init(frame: CGRect) {
        super.init(frame: frame)
    }
    
    required public init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    // MARK: - Segments
    
    struct Segment: Comparable {
        let ratio: CGFloat
        let color: UIColor
        
        static func < (
            lhs: CircularProgressView.Segment,
            rhs: CircularProgressView.Segment
        ) -> Bool {
            return lhs.ratio < rhs.ratio
        }
    }
    
    open var segments: [Segment] = [
        .init(ratio: 0.25, color: .darkGray),
        .init(ratio: 0.4, color: .systemYellow),
        .init(ratio: 0.35, color: .systemBlue),
    ] {
        didSet {
            self.setNeedsDisplay()
        }
    }
    
    // MARK: - Drawing
    
    override open func draw(_ rect: CGRect) {
        drawSegments(segments: segments)
    }
    
    // MARK: - Drawing
    
    private func drawSegments(segments: [Segment]) {
        let center = CGPoint(
            x: bounds.width / 2,
            y: bounds.height / 2
        )
        
        let radius = max(
            bounds.width / 2 - 10,
            bounds.height / 2 - 10
        )
        
        let sortedSegments = segments.sorted(by: >)
        
        var startAngle: CGFloat = (3 * .pi) / 2

        sortedSegments.enumerated().forEach { index, segment in

            let endAngle = (startAngle + (((segment.ratio * 360) * .pi) / 180))
            
            let visibleStartAngle = startAngle * 1.005
            let visibleEndAngle = endAngle * 0.995
            
            drawSegment(
                center: center,
                radius: radius,
                startAngle: visibleStartAngle,
                endAngle: visibleEndAngle,
                color: segment.color
            )
            startAngle = endAngle
        }
    }
    
    private func drawSegment(center: CGPoint, radius: CGFloat, startAngle: CGFloat, endAngle: CGFloat, color: UIColor) {

        let outerPath = UIBezierPath(
            arcCenter: center,
            radius: radius,
            startAngle: startAngle,
            endAngle: endAngle,
            clockwise: true
        )
        
        outerPath.lineWidth = outerThickness
        outerPath.lineCapStyle = .round
        color.setStroke()
        outerPath.stroke()
    }
    
    // MARK: - Starting angles
    
    public enum Angle {
        case degrees(CGFloat)
        case radian(CGFloat)
    }
    
    // MARK: - Thicknesses
    
    @IBInspectable open var outerThickness: CGFloat = 10 {
        didSet {
            self.setNeedsDisplay()
        }
    }
}