Chain Core Animations

CAAnimationChain.swift

/// Core Animation doesn't support chaining of animations by default. The `CAAnimationChain`  class adds this ability.
/// The `CAAnimationSet` struct holds animation set for one target, and `CAAnimationChain` accepts an array of
/// `CAAnimationSet`s to support multiple targets.

import Foundation

class CAAnimationChain: NSObject, CAAnimationDelegate {

    private var animationSets: [CAAnimationSet]
    private let completion: (() -> Void)?

    init(animationSets: [CAAnimationSet], completion: (() -> Void)? = nil) {
        self.animationSets = animationSets
        self.completion = completion
        super.init()

        for animationSet in animationSets {
            for animation in animationSet.animations {
                animation.delegate = self
            }
        }
    }

    // MARK: Chain animations
    public func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
        self.playNext()
    }

    func playNext() {
        guard let animationSet = self.animationSets.first else {
            if let completion = self.completion {
                completion()
            }
            return
        }
        if let animation = animationSet.animations.first {
            if let configuration = animationSet.configuration {
                configuration()
                self.animationSets[0].configuration = nil
            }

            animationSet.target.add(animation, forKey: "currentAnimation")

            self.animationSets[0].animations.removeFirst()
        } else {
            if let completion = animationSet.completion {
                completion()
            }
            self.animationSets.removeFirst()
            self.playNext()
        }
    }
}

struct CAAnimationSet {
    let target: CALayer
    var animations: [CAAnimation]
    var configuration: (() -> Void)?
    let completion: (() -> Void)?
}