A SwiftUI view that performs a looping animation in whole cycles. When the animation is disabled, it drives the current loop to completion, and pauses only then

CycledAnimationTimelineView.swift

struct CycledAnimationTimelineView<Content: View>: View {
	var duration: Double
	var isAnimating: Bool
	@ViewBuilder var content: (Double) -> Content
	
	@State private var isActuallyAnimating = false
	@State private var startDate: Date?
	
	var body: some View {
		TimelineView(.animation(paused: !isActuallyAnimating)) { context in
			content(animationProgress(at: context.date))
		}
		.onChange(of: isAnimating) { isAnimating in
			if isAnimating {
				startAnimation()
			}
		}
		.onAppear {
			if isAnimating {
				startAnimation()
			}
		}
	}
	
	func startAnimation() {
		isActuallyAnimating = true
		if startDate == nil {
			startDate = .now
		}
	}
	
	func animationProgress(at date: Date) -> Double {
		guard isActuallyAnimating else { return 0 }
		
		guard let startDate else {
			DispatchQueue.main.async { startDate = date }
			return 0
		}
		
		let progress = (date.timeIntervalSince(startDate) / duration).truncatingRemainder(dividingBy: 1)
		
		if !isAnimating,
		   progress.isApproximatelyEqual(to: 0, absoluteTolerance: 0.05, norm: \.magnitude) {
			DispatchQueue.main.async {
				isActuallyAnimating = false
				self.startDate = nil
			}
			return .zero
		}
		
		return progress
	}
}