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submodules/TelegramUI/Sources/PreparedChatHistoryViewTransition.swift

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+import Foundation
+import SwiftSignalKit
+import Postbox
+import TelegramCore
+import SyncCore
+import Display
+import MergeLists
+
+func preparedChatHistoryViewTransition(from fromView: ChatHistoryView?, to toView: ChatHistoryView, reason: ChatHistoryViewTransitionReason, reverse: Bool, chatLocation: ChatLocation, controllerInteraction: ChatControllerInteraction, scrollPosition: ChatHistoryViewScrollPosition?, initialData: InitialMessageHistoryData?, keyboardButtonsMessage: Message?, cachedData: CachedPeerData?, cachedDataMessages: [MessageId: Message]?, readStateData: [PeerId: ChatHistoryCombinedInitialReadStateData]?, flashIndicators: Bool, updatedMessageSelection: Bool) -> ChatHistoryViewTransition {
+    let mergeResult: (deleteIndices: [Int], indicesAndItems: [(Int, ChatHistoryEntry, Int?)], updateIndices: [(Int, ChatHistoryEntry, Int)])
+    let allUpdated = fromView?.associatedData != toView.associatedData
+    if reverse {
+        mergeResult = mergeListsStableWithUpdatesReversed(leftList: fromView?.filteredEntries ?? [], rightList: toView.filteredEntries, allUpdated: allUpdated)
+    } else {
+        mergeResult = mergeListsStableWithUpdates(leftList: fromView?.filteredEntries ?? [], rightList: toView.filteredEntries, allUpdated: allUpdated)
+    }
+    
+    var adjustedDeleteIndices: [ListViewDeleteItem] = []
+    let previousCount: Int
+    if let fromView = fromView {
+        previousCount = fromView.filteredEntries.count
+    } else {
+        previousCount = 0
+    }
+    for index in mergeResult.deleteIndices {
+        adjustedDeleteIndices.append(ListViewDeleteItem(index: previousCount - 1 - index, directionHint: nil))
+    }
+    
+    var adjustedIndicesAndItems: [ChatHistoryViewTransitionInsertEntry] = []
+    var adjustedUpdateItems: [ChatHistoryViewTransitionUpdateEntry] = []
+    let updatedCount = toView.filteredEntries.count
+    
+    var options: ListViewDeleteAndInsertOptions = []
+    var animateIn = false
+    var maxAnimatedInsertionIndex = -1
+    var stationaryItemRange: (Int, Int)?
+    var scrollToItem: ListViewScrollToItem?
+    
+    switch reason {
+    case let .Initial(fadeIn):
+        if fadeIn {
+            animateIn = true
+        } else {
+            let _ = options.insert(.LowLatency)
+            let _ = options.insert(.Synchronous)
+            let _ = options.insert(.PreferSynchronousResourceLoading)
+        }
+    case .InteractiveChanges:
+        let _ = options.insert(.AnimateAlpha)
+        let _ = options.insert(.AnimateInsertion)
+        
+        for (index, _, _) in mergeResult.indicesAndItems.sorted(by: { $0.0 > $1.0 }) {
+            let adjustedIndex = updatedCount - 1 - index
+            if adjustedIndex == maxAnimatedInsertionIndex + 1 {
+                maxAnimatedInsertionIndex += 1
+            }
+        }
+    case .Reload:
+        stationaryItemRange = (0, Int.max)
+    case .HoleReload:
+        stationaryItemRange = (0, Int.max)
+    }
+    
+    for (index, entry, previousIndex) in mergeResult.indicesAndItems {
+        let adjustedIndex = updatedCount - 1 - index
+        
+        let adjustedPrevousIndex: Int?
+        if let previousIndex = previousIndex {
+            adjustedPrevousIndex = previousCount - 1 - previousIndex
+        } else {
+            adjustedPrevousIndex = nil
+        }
+        
+        var directionHint: ListViewItemOperationDirectionHint?
+        if maxAnimatedInsertionIndex >= 0 && adjustedIndex <= maxAnimatedInsertionIndex {
+            directionHint = .Down
+        }
+        
+        adjustedIndicesAndItems.append(ChatHistoryViewTransitionInsertEntry(index: adjustedIndex, previousIndex: adjustedPrevousIndex, entry: entry, directionHint: directionHint))
+    }
+    
+    for (index, entry, previousIndex) in mergeResult.updateIndices {
+        let adjustedIndex = updatedCount - 1 - index
+        let adjustedPreviousIndex = previousCount - 1 - previousIndex
+        
+        let directionHint: ListViewItemOperationDirectionHint? = nil
+        adjustedUpdateItems.append(ChatHistoryViewTransitionUpdateEntry(index: adjustedIndex, previousIndex: adjustedPreviousIndex, entry: entry, directionHint: directionHint))
+    }
+    
+    var scrolledToIndex: MessageHistoryAnchorIndex?
+    
+    if let scrollPosition = scrollPosition {
+        switch scrollPosition {
+            case let .unread(unreadIndex):
+                var index = toView.filteredEntries.count - 1
+                for entry in toView.filteredEntries {
+                    if case .UnreadEntry = entry {
+                        scrollToItem = ListViewScrollToItem(index: index, position: .bottom(0.0), animated: false, curve: .Default(duration: nil), directionHint: .Down)
+                        break
+                    }
+                    index -= 1
+                }
+                
+                if scrollToItem == nil {
+                    var index = toView.filteredEntries.count - 1
+                    for entry in toView.filteredEntries {
+                        if entry.index >= unreadIndex {
+                            scrollToItem = ListViewScrollToItem(index: index, position: .bottom(0.0), animated: false, curve: .Default(duration: nil),  directionHint: .Down)
+                            break
+                        }
+                        index -= 1
+                    }
+                }
+                
+                if scrollToItem == nil {
+                    var index = 0
+                    for entry in toView.filteredEntries.reversed() {
+                        if entry.index < unreadIndex {
+                            scrollToItem = ListViewScrollToItem(index: index, position: .bottom(0.0), animated: false, curve: .Default(duration: nil), directionHint: .Down)
+                            break
+                        }
+                        index += 1
+                    }
+                }
+            case let .positionRestoration(scrollIndex, relativeOffset):
+                var index = toView.filteredEntries.count - 1
+                for entry in toView.filteredEntries {
+                    if entry.index >= scrollIndex {
+                        scrollToItem = ListViewScrollToItem(index: index, position: .top(relativeOffset), animated: false, curve: .Default(duration: nil),  directionHint: .Down)
+                        break
+                    }
+                    index -= 1
+                }
+                
+                if scrollToItem == nil {
+                    var index = 0
+                    for entry in toView.filteredEntries.reversed() {
+                        if entry.index < scrollIndex {
+                            scrollToItem = ListViewScrollToItem(index: index, position: .top(0.0), animated: false, curve: .Default(duration: nil), directionHint: .Down)
+                            break
+                        }
+                        index += 1
+                    }
+                }
+            case let .index(scrollIndex, position, directionHint, animated):
+                if case .center = position {
+                    scrolledToIndex = scrollIndex
+                }
+                var index = toView.filteredEntries.count - 1
+                for entry in toView.filteredEntries {
+                    if scrollIndex.isLessOrEqual(to: entry.index) {
+                        scrollToItem = ListViewScrollToItem(index: index, position: position, animated: animated, curve: .Default(duration: nil), directionHint: directionHint)
+                        break
+                    }
+                    index -= 1
+                }
+                
+                if scrollToItem == nil {
+                    var index = 0
+                    for entry in toView.filteredEntries.reversed() {
+                        if !scrollIndex.isLess(than: entry.index) {
+                            scrollToItem = ListViewScrollToItem(index: index, position: position, animated: animated, curve: .Default(duration: nil), directionHint: directionHint)
+                            break
+                        }
+                        index += 1
+                    }
+                }
+        }
+    }
+    
+    if updatedMessageSelection {
+        options.insert(.Synchronous)
+    }
+    
+    return ChatHistoryViewTransition(historyView: toView, deleteItems: adjustedDeleteIndices, insertEntries: adjustedIndicesAndItems, updateEntries: adjustedUpdateItems, options: options, scrollToItem: scrollToItem, stationaryItemRange: stationaryItemRange, initialData: initialData, keyboardButtonsMessage: keyboardButtonsMessage, cachedData: cachedData, cachedDataMessages: cachedDataMessages, readStateData: readStateData, scrolledToIndex: scrolledToIndex, animateIn: animateIn, reason: reason, flashIndicators: flashIndicators)
+}