ContentView.swift

//
//  ContentView.swift
//  BreatheUI WatchKit Extension
//
//  Created by Joel Bernstein on 6/24/19.
//  Copyright © 2019 Joel Bernstein. All rights reserved.
//

import SwiftUI

struct ContentView : View {

    @State var minutes = 1.0
    
    var circleCount: Double { minutes + 5 }
    var roundedCircleCount: Int { Int(ceil(circleCount)) }
    
    var body: some View {
        GeometryReader { proxy in
            ZStack {
                ForEach(1...self.roundedCircleCount) { index in
                    Circle()
                        .rotation(self.calculateAngle(index), anchor: UnitPoint(x: 0.5, y: 1))
                        .scale(0.57)
                        .position(CGPoint(x: proxy.size.width * 0.5, y: proxy.size.width * 0.25))
                        .foregroundColor(Color.white.opacity(self.calculateOpacity(index)))
                }
            }
        }
        .focusable(true)
        .digitalCrownRotation($minutes, from: 1, through: 5, by: 1, sensitivity: .low, isContinuous: false, isHapticFeedbackEnabled: true)
    }
    
    func calculateAngle(_ index: Int) -> Angle
    {
        return .degrees(-((Double(index) - 0.5) * (360.0 / self.circleCount)))
    }
    
    func calculateOpacity(_ index: Int) -> Double
    {
        let fadeThreshold = floor(circleCount)
        
        return index <= Int(fadeThreshold) ? 0.5 : 0.5 * ( circleCount - fadeThreshold )
    }
}

#if DEBUG
struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}
#endif