InfinityAnimation.swift

struct ContentView: View {
    @State private var flag = false
    
    var body: some View {
        GeometryReader { proxy in
            ZStack(alignment: .topLeading) {
                
                // Draw the Infinity Shape
                InfinityShape().stroke(Color.purple, style: StrokeStyle(lineWidth: 5, lineCap: .round, lineJoin: .miter, miterLimit: 0, dash: [7, 7], dashPhase: 0))
                    .foregroundColor(.blue)
                    .frame(width: proxy.size.width, height: 300)
                
                // Animate movement of Image
                Image(systemName: "airplane").resizable().foregroundColor(Color.red)
                    .frame(width: 50, height: 50).offset(x: -25, y: -25)
                    .modifier(FollowEffect(pct: self.flag ? 1 : 0, path: InfinityShape.createInfinityPath(in: CGRect(x: 0, y: 0, width: proxy.size.width, height: 300)), rotate: true))
                    .onAppear {
                        withAnimation(Animation.linear(duration: 4.0).repeatForever(autoreverses: false)) {
                            self.flag.toggle()
                        }
                    }
                
            }.frame(alignment: .topLeading)
        }
    }
}

struct FollowEffect: GeometryEffect {
    var pct: CGFloat = 0
    let path: Path
    var rotate = true
    
    var animatableData: CGFloat {
        get { return pct }
        set { pct = newValue }
    }
    
    func effectValue(size: CGSize) -> ProjectionTransform {
        
        if !rotate {
            let pt = percentPoint(pct)
            
            return .init(.init(translationX: pt.x, y: pt.y))
        } else {
            let pt1 = percentPoint(pct)
            let pt2 = percentPoint(pct - 0.01)
            
            let a = pt2.x - pt1.x
            let b = pt2.y - pt1.y
            
            let angle = a < 0 ? atan(Double(b / a)) : atan(Double(b / a)) - Double.pi
            
            let transform = CGAffineTransform(translationX: pt1.x, y: pt1.y).rotated(by: CGFloat(angle))
            
            return .init(transform)
        }
    }
    
    func percentPoint(_ percent: CGFloat) -> CGPoint {
        
        let pct = percent > 1 ? 0 : (percent < 0 ? 1 : percent)
        
        let f = pct > 0.999 ? CGFloat(1-0.001) : pct
        let t = pct > 0.999 ? CGFloat(1) : pct + 0.001
        let tp = path.trimmedPath(from: f, to: t)
        
        return CGPoint(x: tp.boundingRect.midX, y: tp.boundingRect.midY)
    }
}

struct InfinityShape: Shape {
    func path(in rect: CGRect) -> Path {
        return InfinityShape.createInfinityPath(in: rect)
    }

    static func createInfinityPath(in rect: CGRect) -> Path {
        let height = rect.size.height
        let width = rect.size.width
        let heightFactor = height/4
        let widthFactor = width/4
        
        let path = UIBezierPath()
        path.lineWidth = 3.0
        
        path.move(to: CGPoint(x:widthFactor, y: heightFactor * 3))
        path.addCurve(to: CGPoint(x:widthFactor, y: heightFactor), controlPoint1: CGPoint(x:0, y: heightFactor * 3), controlPoint2: CGPoint(x:0, y: heightFactor))
        
        path.move(to: CGPoint(x:widthFactor, y: heightFactor))
        path.addCurve(to: CGPoint(x:widthFactor * 3, y: heightFactor * 3), controlPoint1: CGPoint(x:widthFactor * 2, y: heightFactor), controlPoint2: CGPoint(x:widthFactor * 2, y: heightFactor * 3))
        
        path.move(to: CGPoint(x:widthFactor * 3, y: heightFactor * 3))
        path.addCurve(to: CGPoint(x:widthFactor * 3, y: heightFactor), controlPoint1: CGPoint(x:widthFactor * 4 + 5, y: heightFactor * 3), controlPoint2: CGPoint(x:widthFactor * 4 + 5, y: heightFactor))
        
        path.move(to: CGPoint(x:widthFactor * 3, y: heightFactor))
        path.addCurve(to: CGPoint(x:widthFactor, y: heightFactor * 3), controlPoint1: CGPoint(x:widthFactor * 2, y: heightFactor), controlPoint2: CGPoint(x:widthFactor * 2, y: heightFactor * 3))
        
        return Path(path.cgPath)
    }
}