Animator with Easing

Animator.swift

import Foundation
import CoreGraphics
#if os(iOS)
import UIKit
#endif

struct Animator {
    
    enum AnimationEase {
        case linear
        case easeIn
        case easeInOut
        case easeOut
    }
    
    @discardableResult
    static func animate(for duration: CGFloat,
                        ease: AnimationEase = .linear,
                        loop: @escaping (CGFloat) -> (),
                        done: (() -> ())? = nil) -> Timer {
        
        let startTime: Date = .now
        
        #if os(macOS)
        let refreshRate: Double = {
            let id = CGMainDisplayID()
            guard let display = CGDisplayCopyDisplayMode(id) else { return 60 }
            return display.refreshRate
        }()
        #elseif os(visionOS)
        let refreshRate = 90.0
        #else
        let refreshRate = Double(UIScreen.main.maximumFramesPerSecond)
        #endif
        
        loop(0.0)
    
        return .scheduledTimer(withTimeInterval: 1.0 / refreshRate, repeats: true) { timer in
            
            let elapsedTime = CGFloat(-startTime.timeIntervalSinceNow)
            let fraction = min(elapsedTime / duration, 1.0)
            
            let easeFraction = switch ease {
            case .linear:
                fraction
            case .easeIn:
                cos(fraction * .pi / 2 - .pi) + 1
            case .easeInOut: 
                cos(fraction * .pi - .pi) / 2 + 0.5
            case .easeOut: 
                cos(fraction * .pi / 2 - .pi / 2)
            }
            
            loop(easeFraction)
            
            if fraction == 1.0 {
                done?()
                timer.invalidate()
            }
        }
    }
}