coreanimation.swift

/*
 Copyright 2016-present The Material Motion Authors. All Rights Reserved.

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */

import Foundation

public class TweenAnimation<A: CAAnimation, T>: CustomDebugStringConvertible {
  init(_ animation: A) {
    self.animation = animation
  }
  let animation: A
  var layer: CALayer?
  var key = NSUUID().uuidString

  public var debugDescription: String {
    return "\(animation.debugDescription) '\(key)'"
  }
}

public typealias TweenStream<A: CAAnimation, T> = MotionObservable<TweenAnimation<A, T>>

public func tween<T>(duration: TimeInterval, values: [T]) -> TweenStream<CAKeyframeAnimation, T> {
  return TweenStream(OP(#function, args: [duration, values]), subscriber: { observer in

    CATransaction.begin()

    CATransaction.setCompletionBlock({ 
      observer.state(.atRest)
    })
    observer.state(.active)

    let animation = CAKeyframeAnimation()
    animation.duration = duration
    animation.values = values

    let tween = TweenAnimation<CAKeyframeAnimation, T>(animation)
    observer.next(tween)

    CATransaction.commit()

    return {
      if let layer = tween.layer {
        layer.removeAnimation(forKey: tween.key)
      }
    }
  })
}

extension CALayerPropertyBuilder {
  func opacity<A: CAPropertyAnimation>(_ key: String? = nil) -> Property<TweenAnimation<A, CGFloat>> {
    let layer = self.layer
    return Property(#function, object: layer, read: {
      guard let key = key else {
        assertionFailure("Unable to read nameless animations from CALayer.")
        return TweenAnimation(A())
      }
      return TweenAnimation<A, CGFloat>(layer.animation(forKey: key) as! A)
    }, write: { tween in
      tween.animation.keyPath = "opacity"
      if let key = key {
        tween.key = key
      }
      tween.layer = layer
      layer.add(tween.animation, forKey: tween.key)
    })
  }

  func backgroundColor<A: CAKeyframeAnimation>(_ key: String? = nil) -> Property<TweenAnimation<A, UIColor>> {
    let layer = self.layer
    return Property(#function, object: layer, read: {
      guard let key = key else {
        assertionFailure("Unable to read nameless animations from CALayer.")
        return TweenAnimation(A())
      }
      return TweenAnimation<A, UIColor>(layer.animation(forKey: key) as! A)
    }, write: { tween in
      tween.animation.keyPath = "backgroundColor"
      tween.animation.values = (tween.animation.values as! [UIColor]).map { $0.cgColor }
      if let key = key {
        tween.key = key
      }
      tween.layer = layer
      layer.add(tween.animation, forKey: tween.key)
    })
  }
}