ActivityIndicatorView/Source/Indicators/ScalingDotsIndicatorView.swift

//
//  ScalingDotsIndicatorView.swift
//  ActivityIndicatorView
//
//  Created by Daniil Manin on 10/7/20.
//  Copyright © 2020 Exyte. All rights reserved.
//

import SwiftUI

struct ScalingDotsIndicatorView: View {

    private let count: Int = 3
    private let inset: Int = 2

    var body: some View {
        GeometryReader { geometry in
            ForEach(0..<self.count) { index in
                ScalingDotsIndicatorItemView(index: index, count: self.count, inset: self.inset, size: geometry.size)
            }.frame(width: geometry.size.width, height: geometry.size.height)
        }
    }
}

struct ScalingDotsIndicatorItemView: View {

    let index: Int
    let count: Int
    let inset: Int
    let size: CGSize

    @State private var scale: CGFloat = 0

    var body: some View {
        let itemSize = (size.width - CGFloat(inset) * CGFloat(count - 1)) / CGFloat(count)

        let animation = Animation.easeOut
            .repeatForever(autoreverses: true)
            .delay(Double(index) / Double(count) / 2)
        
        return Circle()
            .frame(width: itemSize, height: itemSize)
            .scaleEffect(scale)
            .onAppear {
                self.scale = 1
                withAnimation(animation) {
                    self.scale = 0.3
                }
            }
            .offset(x: (itemSize + CGFloat(inset)) * CGFloat(index) - size.width / 2 + itemSize / 2)
    }
}