MessageKit/Sources/Views/TypingIndicator.swift

/*
 MIT License
 
 Copyright (c) 2017-2019 MessageKit
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in all
 copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */

import UIKit

/// A `UIView` subclass that holds 3 dots which can be animated
open class TypingIndicator: UIView {
    
    // MARK: - Properties
    
    /// The offset that each dot will transform by during the bounce animation
    public var bounceOffset: CGFloat = 2.5
    
    /// A convenience accessor for the `backgroundColor` of each dot
    open var dotColor: UIColor = UIColor.lightGray {
        didSet {
            dots.forEach { $0.backgroundColor = dotColor }
        }
    }
    
    /// A flag that determines if the bounce animation is added in `startAnimating()`
    public var isBounceEnabled: Bool = false
    
    /// A flag that determines if the opacity animation is added in `startAnimating()`
    public var isFadeEnabled: Bool = true
    
    /// A flag indicating the animation state
    public private(set) var isAnimating: Bool = false
    
    /// Keys for each animation layer
    private struct AnimationKeys {
        static let offset = "typingIndicator.offset"
        static let bounce = "typingIndicator.bounce"
        static let opacity = "typingIndicator.opacity"
    }
    
    /// The `CABasicAnimation` applied when `isBounceEnabled` is TRUE to move the dot to the correct
    /// initial offset
    open var initialOffsetAnimationLayer: CABasicAnimation {
        let animation = CABasicAnimation(keyPath: "transform.translation.y")
        animation.byValue = -bounceOffset
        animation.duration = 0.5
        animation.isRemovedOnCompletion = true
        return animation
    }
    
    /// The `CABasicAnimation` applied when `isBounceEnabled` is TRUE
    open var bounceAnimationLayer: CABasicAnimation {
        let animation = CABasicAnimation(keyPath: "transform.translation.y")
        animation.toValue = -bounceOffset
        animation.fromValue = bounceOffset
        animation.duration = 0.5
        animation.repeatCount = .infinity
        animation.autoreverses = true
        return animation
    }
    
    /// The `CABasicAnimation` applied when `isFadeEnabled` is TRUE
    open var opacityAnimationLayer: CABasicAnimation {
        let animation = CABasicAnimation(keyPath: "opacity")
        animation.fromValue = 1
        animation.toValue = 0.5
        animation.duration = 0.5
        animation.repeatCount = .infinity
        animation.autoreverses = true
        return animation
    }
    
    // MARK: - Subviews
    
    public let stackView = UIStackView()
    
    public let dots: [BubbleCircle] = {
        return [BubbleCircle(), BubbleCircle(), BubbleCircle()]
    }()
    
    // MARK: - Initialization
    
    public override init(frame: CGRect) {
        super.init(frame: frame)
        setupView()
    }
    
    public required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setupView()
    }
    
    /// Sets up the view
    private func setupView() {
        dots.forEach {
            $0.backgroundColor = dotColor
            $0.heightAnchor.constraint(equalTo: $0.widthAnchor).isActive = true
            stackView.addArrangedSubview($0)
        }
        stackView.axis = .horizontal
        stackView.alignment = .center
        stackView.distribution = .fillEqually
        addSubview(stackView)
    }
    
    // MARK: - Layout
    
    open override func layoutSubviews() {
        super.layoutSubviews()
        stackView.frame = bounds
        stackView.spacing = bounds.width > 0 ? 5 : 0
    }
    
    // MARK: - Animation API
    
    /// Sets the state of the `TypingIndicator` to animating and applies animation layers
    open func startAnimating() {
        defer { isAnimating = true }
        guard !isAnimating else { return }
        var delay: TimeInterval = 0
        for dot in dots {
            DispatchQueue.main.asyncAfter(deadline: .now() + delay) { [weak self] in
                guard let `self` = self else { return }
                if self.isBounceEnabled {
                    dot.layer.add(self.initialOffsetAnimationLayer, forKey: AnimationKeys.offset)
                    let bounceLayer = self.bounceAnimationLayer
                    bounceLayer.timeOffset = delay + 0.33
                    dot.layer.add(bounceLayer, forKey: AnimationKeys.bounce)
                }
                if self.isFadeEnabled {
                    dot.layer.add(self.opacityAnimationLayer, forKey: AnimationKeys.opacity)
                }
            }
            delay += 0.33
        }
    }
    
    /// Sets the state of the `TypingIndicator` to not animating and removes animation layers
    open func stopAnimating() {
        defer { isAnimating = false }
        guard isAnimating else { return }
        dots.forEach {
            $0.layer.removeAnimation(forKey: AnimationKeys.bounce)
            $0.layer.removeAnimation(forKey: AnimationKeys.opacity)
        }
    }
    
}