AppleWalletPaymentRing.swift

import SwiftUI

struct PaymentRing: View {
    @State var frameSize = UIScreen.main.bounds.width - 120
    @State var current: CGFloat = 0
    @State var value: Double = 0
    var body: some View {
        VStack {
            ZStack {
                Circle().stroke(Color.secondary, style: StrokeStyle(lineWidth: 40, lineCap: .butt, lineJoin: .round)).frame(width: frameSize, height: frameSize)
                Circle().trim(from: 0, to: current).stroke(Color.green, style: StrokeStyle(lineWidth: 40, lineCap: .round, lineJoin: .round)).frame(width: frameSize, height: frameSize).rotationEffect(.init(degrees: -90))
                Circle().fill(Color.white).frame(width: 40, height: 40).offset(x: frameSize/2).rotationEffect(.init(degrees: value)).gesture(DragGesture().onChanged(onDrag(value:))).rotationEffect(.init(degrees: -90))
                
                
                HStack {
                    Text("$")
                    Text(String(format: "%.0f", current * 1000)).font(.largeTitle)
                }
            }
        }
    }
    
    func onDrag(value: DragGesture.Value) {
        let radianVector = CGVector(dx: value.location.x, dy: value.location.y)
        let radian = atan2(radianVector.dy - 20, radianVector.dx - 20)
        var angleValue = radian * 180 / .pi
        
        if angleValue < 0 {
            angleValue = 360 + angleValue
        }
        
        withAnimation(Animation.linear(duration: 0.25)) {
            let current = angleValue / 360
            self.current = current
            self.value = Double(angleValue)
        }
    }
}

struct PaymentRing_Previews: PreviewProvider {
    static var previews: some View {
        PaymentRing().preferredColorScheme(.dark)
    }
}