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Chatto/Source/Chat Items/BaseChatItemPresenter.swift

@@ -116,4 +116,8 @@ open class BaseChatItemPresenter<CellT: UICollectionViewCell>: ChatItemPresenter
     open func performMenuControllerAction(_ action: Selector) {
         assert(self.canPerformMenuControllerAction(action))
     }
+
+    // MARK: - ChatItemSpotlighting
+
+    open func spotlight() {}
 }

Chatto/Source/Chat Items/ChatItemProtocolDefinitions.swift

@@ -40,7 +40,15 @@ public protocol ChatItemMenuPresenterProtocol {
     func performMenuControllerAction(_ action: Selector)
 }
 
-public protocol ChatItemPresenterProtocol: AnyObject, ChatItemMenuPresenterProtocol {
+public protocol ChatItemSpotlighting {
+    func spotlight()
+}
+
+extension ChatItemSpotlighting {
+    public func spotlight() {}
+}
+
+public protocol ChatItemPresenterProtocol: AnyObject, ChatItemMenuPresenterProtocol, ChatItemSpotlighting {
     static func registerCells(_ collectionView: UICollectionView)
 
     var isItemUpdateSupported: Bool { get }

Chatto/Source/ChatController/BaseChatViewController+Scrolling.swift

@@ -35,6 +35,12 @@ extension CGFloat {
 
 extension BaseChatViewController {
 
+    private static var nextDidEndScrollingAnimationHandlersKey: Int = 0
+    private var nextDidEndScrollingAnimationHandlers: [() -> Void] {
+        get { objc_getAssociatedObject(self, &Self.nextDidEndScrollingAnimationHandlersKey) as? [() -> Void] ?? [] }
+        set { objc_setAssociatedObject(self, &Self.nextDidEndScrollingAnimationHandlersKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC) }
+    }
+
     public func isScrolledAtBottom() -> Bool {
         guard let collectionView = self.collectionView else { return true }
         guard collectionView.numberOfSections > 0 && collectionView.numberOfItems(inSection: 0) > 0 else { return true }
@@ -113,7 +119,10 @@ extension BaseChatViewController {
         collectionView.contentOffset = CGPoint(x: 0, y: collectionView.contentOffset.y + diffY)
     }
 
-    public func scrollToItem(withId itemId: String, position: UICollectionView.ScrollPosition = .centeredVertically, animated: Bool = false) {
+    public func scrollToItem(withId itemId: String,
+                             position: UICollectionView.ScrollPosition = .centeredVertically,
+                             animated: Bool = false,
+                             spotlight: Bool = false) {
         guard let collectionView = self.collectionView else { return }
         guard let itemIndex = self.chatItemCompanionCollection.indexOf(itemId) else { return }
 
@@ -143,9 +152,28 @@ extension BaseChatViewController {
             }
         }
 
+        if spotlight {
+            guard let presenter = self.chatItemCompanionCollection[itemId]?.presenter else { return }
+            let contentOffsetWillBeChanged = !collectionView.indexPathsForVisibleItems.contains(indexPath)
+            if contentOffsetWillBeChanged {
+                self.nextDidEndScrollingAnimationHandlers.append { [weak presenter] in
+                    presenter?.spotlight()
+                }
+            } else {
+                presenter.spotlight()
+            }
+        }
+
         collectionView.scrollToItem(at: indexPath, at: position, animated: animated)
     }
 
+    open func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
+        for handler in self.nextDidEndScrollingAnimationHandlers {
+            handler()
+        }
+        self.nextDidEndScrollingAnimationHandlers = []
+    }
+
     open func scrollViewDidScroll(_ scrollView: UIScrollView) {
         guard let collectionView = self.collectionView else { return }
         if collectionView.isDragging {

ChattoAdditions/Source/Chat Items/CompoundMessage/CompoundMessagePresenter.swift

@@ -264,6 +264,12 @@ open class CompoundMessagePresenter<ViewModelBuilderT, InteractionHandlerT>
         self.menuPresenter?.performMenuControllerAction(action)
     }
 
+    // MARK: - ChatItemSpotlighting
+
+    override open func spotlight() {
+        self.cell?.bubbleView?.spotlight()
+    }
+
     // MARK: - MessageContentPresenterDelegate
 
     public func presenterDidInvalidateLayout(_ presenter: MessageContentPresenterProtocol) {

ChattoAdditions/Source/Chat Items/CompoundMessage/Views/CompoundBubbleView.swift

@@ -82,6 +82,32 @@ public final class CompoundBubbleView: UIView, MaximumLayoutWidthSpecificable, B
         didSet { self.setNeedsLayout() }
     }
 
+    // MARK: - Spotlighting
+
+    public func spotlight() {
+        // Covers the case when bubble is hidden
+        guard self.backgroundColor != nil else { return }
+
+        guard let viewModel = self.viewModel,
+              let style = self.style,
+              let spotlightedColor = style.spotlightedBackgroundColor(forViewModel: viewModel),
+              let originalColor = style.backgroundColor(forViewModel: viewModel) else { return }
+
+        let durationInMs = Int(style.spotlightDuration(forViewModel: viewModel) * 1000)
+
+        self.animateBackgroundColorChange(to: spotlightedColor)
+        DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(durationInMs)) { [weak self] in
+            self?.animateBackgroundColorChange(to: originalColor)
+        }
+    }
+
+    private static let backgroundColorChangeAnimationDuration: TimeInterval = 0.1
+    private func animateBackgroundColorChange(to color: UIColor) {
+        UIView.animate(withDuration: Self.backgroundColorChangeAnimationDuration) { [weak self] in
+            self?.backgroundColor = color
+        }
+    }
+
     // MARK: - MaximumLayoutWidthSpecificable
 
     public var preferredMaxLayoutWidth: CGFloat = 0

ChattoAdditions/Source/Chat Items/CompoundMessage/Views/CompoundBubbleViewStyle.swift

@@ -27,6 +27,8 @@ public protocol CompoundBubbleViewStyleProtocol {
     typealias ViewModel = MessageViewModelProtocol
     var hideBubbleForSingleContent: Bool { get }
     func backgroundColor(forViewModel viewModel: ViewModel) -> UIColor?
+    func spotlightedBackgroundColor(forViewModel viewModel: ViewModel) -> UIColor?
+    func spotlightDuration(forViewModel viewModel: ViewModel) -> TimeInterval
     func maskingImage(forViewModel viewModel: ViewModel) -> UIImage?
     func borderImage(forViewModel viewModel: ViewModel) -> UIImage?
     func tailWidth(forViewModel viewModel: ViewModel) -> CGFloat
@@ -55,13 +57,19 @@ public final class DefaultCompoundBubbleViewStyle: CompoundBubbleViewStyleProtoc
 
     private let baseStyle: BaseMessageCollectionViewCellDefaultStyle
     private let bubbleMasks: BubbleMasks
+    private let spotlightBrightnessScale: CGFloat
+    private let spotlightDuration: TimeInterval
 
     public init(baseStyle: BaseMessageCollectionViewCellDefaultStyle = BaseMessageCollectionViewCellDefaultStyle(),
                 bubbleMasks: BubbleMasks = .default,
-                hideBubbleForSingleContent: Bool = false) {
+                hideBubbleForSingleContent: Bool = false,
+                spotlightBrightnessScale: CGFloat = 0.85,
+                spotlightDuration: TimeInterval = 0.5) {
         self.baseStyle = baseStyle
         self.bubbleMasks = bubbleMasks
         self.hideBubbleForSingleContent = hideBubbleForSingleContent
+        self.spotlightBrightnessScale = spotlightBrightnessScale
+        self.spotlightDuration = spotlightDuration
     }
 
     // MARK: CompoundBubbleViewStyleProtocol
@@ -72,6 +80,14 @@ public final class DefaultCompoundBubbleViewStyle: CompoundBubbleViewStyleProtoc
         return viewModel.isIncoming ? self.baseStyle.baseColorIncoming : self.baseStyle.baseColorOutgoing
     }
 
+    public func spotlightedBackgroundColor(forViewModel viewModel: ViewModel) -> UIColor? {
+        self.backgroundColor(forViewModel: viewModel)?.changeBrightness(to: self.spotlightBrightnessScale)
+    }
+
+    public func spotlightDuration(forViewModel viewModel: ViewModel) -> TimeInterval {
+        self.spotlightDuration
+    }
+
     public func maskingImage(forViewModel viewModel: ViewModel) -> UIImage? {
         return self.bubbleMasks.image(incoming: viewModel.isIncoming,
                                       showTail: viewModel.decorationAttributes.isShowingTail)
@@ -111,3 +127,23 @@ extension DefaultCompoundBubbleViewStyle.BubbleMasks {
         )
     }
 }
+
+private extension UIColor {
+    func changeBrightness(to scale: CGFloat) -> UIColor {
+        var red: CGFloat = 0
+        var green: CGFloat = 0
+        var blue: CGFloat = 0
+        var alpha: CGFloat = 0
+
+        guard self.getRed(&red, green: &green, blue: &blue, alpha: &alpha) else {
+            assertionFailure("Couldn't get colors of: \(self)")
+            return self
+        }
+
+        red *= scale
+        green *= scale
+        blue *= scale
+
+        return UIColor(red: red, green: green, blue: blue, alpha: alpha)
+    }
+}