AnimatedIndicator

//
//  ContentView.swift
//  ActivityIndicator
//
//  Created by Chris Eidhof on 11.06.19.
//  Copyright © 2019 Chris Eidhof. All rights reserved.
//

import SwiftUI
import Combine

final class TimedCounter: BindableObject {
    var counter: Int = 0 {
        didSet {
            didChange.send(counter)
        }
    }
    let didChange = PassthroughSubject<Int, Never>()
    var timer: Timer! = nil
    init(interval: TimeInterval) {
        timer = Timer.scheduledTimer(withTimeInterval: interval, repeats: true, block: { _ in
            self.counter += 1
        })
    }
    deinit {
        timer?.invalidate()
    }
}

struct RelativePosition: ViewModifier {
    let x, y: CGFloat
    init(x: CGFloat, y: CGFloat) {
        self.x = x
        self.y = y
    }
    func body(content: Content) -> some View {
        GeometryReader { proxy in
            content.position(x: self.x * proxy.size.width, y: self.y * proxy.size.height)
        }

    }
}

extension View {
    func relativePosition(x: CGFloat, y: CGFloat) -> some View {
        return Modified(content: self, modifier: RelativePosition(x: x, y: y))
    }
}

struct ActivityIndicator: View {
    @ObjectBinding var timer: TimedCounter
    let speed: TimeInterval
    init(speed: TimeInterval = 2) {
        timer = TimedCounter(interval: speed)
        self.speed = speed
    }
    var body: ActivityIndicatorContent {
        return ActivityIndicatorContent(count: $timer.counter, speed: speed)
    }
}

struct ActivityIndicatorContent: View {
    @Binding var count: Int
    let numberOfSegments: Int
    let speed: TimeInterval
    init(count: Binding<Int>, numberOfSegments: Int = 10, speed: TimeInterval) {
        self.numberOfSegments = numberOfSegments
        self.$count = count
        self.speed = speed
    }
    let relativeHeight: CGFloat = 0.25
    var y: CGFloat {
        return relativeHeight - (CGFloat(numberOfSegments)/80)
    }
    let from: Color = .black
    var body: some View {
        ZStack {
            ForEach(0..<self.numberOfSegments) { num in
                Capsule()
                    .fill(self.from)
                    .brightness(Double(num)/Double(self.numberOfSegments))
                    .relativeSize(width: 0.1, height: self.relativeHeight)
                    .relativePosition(x: 0.5, y: self.y)
                    .rotationEffect(.degrees(Double(num) * (360/Double(self.numberOfSegments))), anchor: .center)
            }
        }.drawingGroup()
        .rotationEffect(Angle.degrees(Double(count) * 360))
        .animation(Animation.basic(duration: speed))
    }
}

struct ContentView : View {
    var body: some View {
        VStack {
            ActivityIndicator()
            .frame(width: 50, height: 50)
        }
        
    }
}

#if DEBUG
struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
        Group {
            ForEach(1..<10) { _ in
                ActivityIndicator()
                    .frame(width: 50, height: 50)
            }
        }
        
    }
}
#endif