//

// KeyframeAnimation.swift

// VideoLab

//

// Created by Bear on 2020/8/13.

// Copyright © 2020 Chocolate. All rights reserved.

//

import CoreMedia

public struct KeyframeAnimation {

/// The key-path describing the property to be animated.

public var keyPath: String

/// An array providing the value of the animation function for each keyframe.

public var values: [Float]

/// An array of `CMTime' objects defining the pacing of the animation.

/// Each time corresponds to one value in the `values' array, time is based on layer time.

public var keyTimes: [CMTime]

/// An optional array of TimingFunction objects.

/// If the `values' array defines n keyframes, there should be n-1 objects in the `timingFunctions' array

public var timingFunctions: [TimingFunction]

/// Create a KeyframeAnimation with keyPath, values, keyTimes, timingFunctions

public init(keyPath: String, values: [Float], keyTimes: [CMTime], timingFunctions: [TimingFunction]) {

self.keyPath = keyPath

self.values = values

self.keyTimes = keyTimes

self.timingFunctions = timingFunctions

}

/// The value at the corresponding time, time is based on layer time.

public func value(at time: CMTime) -> Float? {

let timeValue = time.seconds

for index in 0..<keyTimes.count - 1 {

let startTimeValue = keyTimes[index].seconds

let endTimeValue = keyTimes[index + 1].seconds

// Less than the minimum time

if index == 0 && timeValue < startTimeValue {

return values[0]

}

// Greater than maximum time

if index == keyTimes.count - 2 && timeValue > endTimeValue {

return values[index + 1]

}

if timeValue >= startTimeValue && timeValue <= endTimeValue {

let progress = Float(timeValue - startTimeValue) / Float(endTimeValue - startTimeValue)

let timingFunction = timingFunctions[index]

let normalizedValue = timingFunction.value(at: progress)

let fromValue = values[index]

let toValue = values[index + 1]

let value = fromValue + normalizedValue * (toValue - fromValue)

return value

}

}

return nil

}

public static func value(for keyPath: String, at time: CMTime, animations: [KeyframeAnimation]?) -> Float? {

guard let animations = animations else {

return nil

}

for animation in animations {

if animation.keyPath == keyPath {

if let value = animation.value(at: time) {

return value

}

}

}

return nil

}

}

public protocol Animatable {

var animations: [KeyframeAnimation]? { get set }

mutating func updateAnimationValues(at time: CMTime)

}