Externalize creation of Chat collection view layout models

Chatto/Chatto.xcodeproj/project.pbxproj

@@ -16,6 +16,8 @@
 		A410D4BD26C570B100A48342 /* ChatMessagesViewControllerHelpers.swift in Sources */ = {isa = PBXBuildFile; fileRef = A410D4BC26C570B100A48342 /* ChatMessagesViewControllerHelpers.swift */; };
 		A42C66DE273BC387006B032A /* TimingChatInputBarAnimation.swift in Sources */ = {isa = PBXBuildFile; fileRef = A42C66DD273BC387006B032A /* TimingChatInputBarAnimation.swift */; };
 		A42C66E0273BC3B1006B032A /* SpringChatInputBarAnimation.swift in Sources */ = {isa = PBXBuildFile; fileRef = A42C66DF273BC3B1006B032A /* SpringChatInputBarAnimation.swift */; };
+		A441C27C2787442C00988636 /* ChatCollectionViewLayoutModelFactory.swift in Sources */ = {isa = PBXBuildFile; fileRef = A441C27B2787442C00988636 /* ChatCollectionViewLayoutModelFactory.swift */; };
+		A441C27E2787446C00988636 /* ChatCollectionItemsDiffer.swift in Sources */ = {isa = PBXBuildFile; fileRef = A441C27D2787446C00988636 /* ChatCollectionItemsDiffer.swift */; };
 		A452A8C12705DAED00DCC8D5 /* Observable.swift in Sources */ = {isa = PBXBuildFile; fileRef = A452A8BF2705DAED00DCC8D5 /* Observable.swift */; };
 		A4724CDB27355829006B9562 /* ChatPanGestureRecogniserHandler.swift in Sources */ = {isa = PBXBuildFile; fileRef = A4724CDA27355829006B9562 /* ChatPanGestureRecogniserHandler.swift */; };
 		A4C03CFE26CE431D00360526 /* ChatInputBarPresenterProtocol.swift in Sources */ = {isa = PBXBuildFile; fileRef = A4C03CFD26CE431D00360526 /* ChatInputBarPresenterProtocol.swift */; };
@@ -69,6 +71,8 @@
 		A410D4BC26C570B100A48342 /* ChatMessagesViewControllerHelpers.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatMessagesViewControllerHelpers.swift; sourceTree = "<group>"; };
 		A42C66DD273BC387006B032A /* TimingChatInputBarAnimation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TimingChatInputBarAnimation.swift; sourceTree = "<group>"; };
 		A42C66DF273BC3B1006B032A /* SpringChatInputBarAnimation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SpringChatInputBarAnimation.swift; sourceTree = "<group>"; };
+		A441C27B2787442C00988636 /* ChatCollectionViewLayoutModelFactory.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatCollectionViewLayoutModelFactory.swift; sourceTree = "<group>"; };
+		A441C27D2787446C00988636 /* ChatCollectionItemsDiffer.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatCollectionItemsDiffer.swift; sourceTree = "<group>"; };
 		A452A8BF2705DAED00DCC8D5 /* Observable.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Observable.swift; sourceTree = "<group>"; };
 		A4724CDA27355829006B9562 /* ChatPanGestureRecogniserHandler.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ChatPanGestureRecogniserHandler.swift; sourceTree = "<group>"; };
 		A4C03CFD26CE431D00360526 /* ChatInputBarPresenterProtocol.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatInputBarPresenterProtocol.swift; sourceTree = "<group>"; };
@@ -224,6 +228,8 @@
 				A4F7666226BD417600008F24 /* ChatMessagesViewController.swift */,
 				A4F7666526BD4FA400008F24 /* ChatMessageCollectionAdapter.swift */,
 				A4F7666726BD59EF00008F24 /* ChatMessagesViewModel.swift */,
+				A441C27B2787442C00988636 /* ChatCollectionViewLayoutModelFactory.swift */,
+				A441C27D2787446C00988636 /* ChatCollectionItemsDiffer.swift */,
 			);
 			path = ChatMessages;
 			sourceTree = "<group>";
@@ -440,6 +446,8 @@
 				A42C66DE273BC387006B032A /* TimingChatInputBarAnimation.swift in Sources */,
 				C36281E71BF0F196004D6BCE /* UICollectionView+Scrolling.swift in Sources */,
 				26D653F2251043BD007BC13C /* ReplyFeedbackGenerator.swift in Sources */,
+				A441C27E2787446C00988636 /* ChatCollectionItemsDiffer.swift in Sources */,
+				A441C27C2787442C00988636 /* ChatCollectionViewLayoutModelFactory.swift in Sources */,
 				3565429D203DB99300B29DA1 /* ChatLayoutConfiguration.swift in Sources */,
 				C36281EB1BF0F62F004D6BCE /* DummyChatItemPresenter.swift in Sources */,
 				C3C7C3981CAC4BAC00A49929 /* ChatCollectionViewLayout.swift in Sources */,

Chatto/sources/ChatController/ChatMessages/ChatCollectionItemsDiffer.swift

@@ -0,0 +1,88 @@
+//
+// Copyright (c) Bumble, 2021-present. All rights reserved.
+//
+
+import CoreGraphics
+
+final class ChatCollectionItemsDiffer {
+
+    struct Diff {
+        let changes: CollectionChanges
+        let itemCompanionCollection: ChatItemCompanionCollection
+        let layoutModel: ChatCollectionViewLayoutModel
+    }
+
+    private let chatItemsDecorator: ChatItemsDecoratorProtocol
+    private let chatItemPresenterFactory: ChatItemPresenterFactoryProtocol
+    private let chatCollectionViewLayoutModelFactory: ChatCollectionViewLayoutModelFactoryProtocol
+
+    init(
+        chatItemsDecorator: ChatItemsDecoratorProtocol,
+        chatItemPresenterFactory: ChatItemPresenterFactoryProtocol,
+        chatCollectionViewLayoutModelFactory: ChatCollectionViewLayoutModelFactoryProtocol
+    ) {
+        self.chatItemsDecorator = chatItemsDecorator
+        self.chatItemPresenterFactory = chatItemPresenterFactory
+        self.chatCollectionViewLayoutModelFactory = chatCollectionViewLayoutModelFactory
+    }
+
+    func calculateChanges(
+        newItems: [ChatItemProtocol],
+        oldItems: ChatItemCompanionCollection,
+        collectionViewWidth: CGFloat
+    ) -> Diff {
+
+        let newDecoratedItems = self.chatItemsDecorator.decorateItems(newItems)
+        let changes = generateChanges(
+            oldCollection: oldItems.map(HashableItem.init),
+            newCollection: newDecoratedItems.map(HashableItem.init)
+        )
+        let itemCompanionCollection = self.createCompanionCollection(fromChatItems: newDecoratedItems, previousCompanionCollection: oldItems)
+        let layoutModel = self.chatCollectionViewLayoutModelFactory.createLayoutModel(itemCompanionCollection, collectionViewWidth: collectionViewWidth)
+
+        return Diff(
+            changes: changes,
+            itemCompanionCollection: itemCompanionCollection,
+            layoutModel: layoutModel
+        )
+    }
+
+    private func createCompanionCollection(fromChatItems newItems: [DecoratedChatItem], previousCompanionCollection oldItems: ChatItemCompanionCollection) -> ChatItemCompanionCollection {
+        return ChatItemCompanionCollection(items: newItems.map { (decoratedChatItem) -> ChatItemCompanion in
+
+            /*
+             We use an assumption, that message having a specific messageId never changes its type.
+             If such changes has to be supported, then generation of changes has to suppport reloading items.
+             Otherwise, updateVisibleCells may try to update the existing cells with new presenters which aren't able to work with another types.
+             */
+
+            let presenter: ChatItemPresenterProtocol = {
+                guard let oldChatItemCompanion = oldItems[decoratedChatItem.uid] ?? oldItems[decoratedChatItem.chatItem.uid],
+                    oldChatItemCompanion.chatItem.type == decoratedChatItem.chatItem.type,
+                    oldChatItemCompanion.presenter.isItemUpdateSupported else {
+                        return self.chatItemPresenterFactory.createChatItemPresenter(decoratedChatItem.chatItem)
+                }
+
+                oldChatItemCompanion.presenter.update(with: decoratedChatItem.chatItem)
+                return oldChatItemCompanion.presenter
+            }()
+
+            return ChatItemCompanion(uid: decoratedChatItem.uid, chatItem: decoratedChatItem.chatItem, presenter: presenter, decorationAttributes: decoratedChatItem.decorationAttributes)
+        })
+    }
+}
+
+private struct HashableItem: Hashable {
+    private let uid: String
+    private let type: String
+
+    init(_ decoratedChatItem: DecoratedChatItem) {
+        self.uid = decoratedChatItem.uid
+        self.type = decoratedChatItem.chatItem.type
+    }
+
+    init(_ chatItemCompanion: ChatItemCompanion) {
+        self.uid = chatItemCompanion.uid
+        self.type = chatItemCompanion.chatItem.type
+    }
+}

Chatto/sources/ChatController/ChatMessages/ChatCollectionViewLayoutModelFactory.swift

@@ -0,0 +1,57 @@
+//
+// Copyright (c) Bumble, 2021-present. All rights reserved.
+//
+
+import CoreGraphics
+import Foundation
+
+public protocol ChatCollectionViewLayoutModelFactoryProtocol {
+    func createLayoutModel(_ items: ChatItemCompanionCollection, collectionViewWidth: CGFloat) -> ChatCollectionViewLayoutModel
+}
+
+public final class ChatCollectionViewLayoutModelFactory: ChatCollectionViewLayoutModelFactoryProtocol {
+
+    public init() { }
+
+    public func createLayoutModel(_ items: ChatItemCompanionCollection, collectionViewWidth: CGFloat) -> ChatCollectionViewLayoutModel {
+        // swiftlint:disable:next nesting
+        typealias IntermediateItemLayoutData = (height: CGFloat?, bottomMargin: CGFloat)
+        typealias ItemLayoutData = (height: CGFloat, bottomMargin: CGFloat)
+        // swiftlint:disable:previous nesting
+
+        func createLayoutModel(intermediateLayoutData: [IntermediateItemLayoutData]) -> ChatCollectionViewLayoutModel {
+            let layoutData = intermediateLayoutData.map { (intermediateLayoutData: IntermediateItemLayoutData) -> ItemLayoutData in
+                return (height: intermediateLayoutData.height!, bottomMargin: intermediateLayoutData.bottomMargin)
+            }
+            return ChatCollectionViewLayoutModel.createModel(collectionViewWidth, itemsLayoutData: layoutData)
+        }
+
+        let isInBackground = !Thread.isMainThread
+        var intermediateLayoutData = [IntermediateItemLayoutData]()
+        var itemsForMainThread = [(index: Int, itemCompanion: ChatItemCompanion)]()
+
+        for (index, itemCompanion) in items.enumerated() {
+            var height: CGFloat?
+            let bottomMargin: CGFloat = itemCompanion.decorationAttributes?.bottomMargin ?? 0
+            if !isInBackground || itemCompanion.presenter.canCalculateHeightInBackground {
+                height = itemCompanion.presenter.heightForCell(maximumWidth: collectionViewWidth, decorationAttributes: itemCompanion.decorationAttributes)
+            } else {
+                itemsForMainThread.append((index: index, itemCompanion: itemCompanion))
+            }
+            intermediateLayoutData.append((height: height, bottomMargin: bottomMargin))
+        }
+
+        if itemsForMainThread.count > 0 {
+            DispatchQueue.main.sync {
+                for (index, itemCompanion) in itemsForMainThread {
+                    let height = itemCompanion.presenter.heightForCell(
+                        maximumWidth: collectionViewWidth,
+                        decorationAttributes: itemCompanion.decorationAttributes
+                    )
+                    intermediateLayoutData[index].height = height
+                }
+            }
+        }
+        return createLayoutModel(intermediateLayoutData: intermediateLayoutData)
+    }
+}