mirror of https://github.com/oxen-io/session-ios
Introduce conversation view mapping; rework conversation view scrolling.
Matthew Chen
6 years ago
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//
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// Copyright (c) 2019 Open Whisper Systems. All rights reserved.
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//
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import Foundation
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@objc
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public class ConversationMessageMapping: NSObject {
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private let viewName: String
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private let group: String?
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// The desired number of the items to load BEFORE the pivot (see below).
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@objc
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public var desiredLength: UInt
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typealias ItemId = String
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// The list currently loaded items
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private var itemIds = [ItemId]()
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// We could use this to detect synchronization errors.
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private var snapshotOfLastUpdate: UInt64?
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// When we enter a conversation, we want to load up to N interactions. This
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// in the "initial load window".
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//
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// We subsequently expand the load window in two directions using two very
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// different behaviors.
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//
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// * We expand the load window "upwards" (backwards in time) only when
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// loadMore() is called, in "pages".
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// * We auto-expand the load window "downwards" (forward in time) to include
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// any new interactions created after the initial load.
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//
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// We define the "pivot" as the last item in the initial load window. This
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// value is only set once.
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//
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// For example, if you enter a conversation with messages, 1..15:
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//
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// 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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//
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// We initially load just the last 5 (if 5 is the initial desired length):
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//
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// 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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// | pivot ^ | <-- load window
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// pivot: 15, desired length=5.
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//
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// If a few more messages (16..18) are sent or received, we'll always load
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// them immediately (they're after the pivot):
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//
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// 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
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// | pivot ^ | <-- load window
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// pivot: 15, desired length=5.
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//
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// To load an additional page of items (perhaps due to user scrolling
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// upward), we extend the desired length and thereby load more items
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// before the pivot.
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//
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// 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
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// | pivot ^ | <-- load window
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// pivot: 15, desired length=10.
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//
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// To reiterate:
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//
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// * The pivot doesn't move.
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// * The desired length applies _before_ the pivot.
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// * Everything after the pivot is auto-loaded.
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//
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// And note: we use the pivot's sort id, not its uniqueId, which works
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// even if the pivot itself is deleted.
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private var pivotSortId: UInt64?
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@objc
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public var canLoadMore = false
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@objc
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public required init(group: String?, desiredLength: UInt) {
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self.viewName = TSMessageDatabaseViewExtensionName
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self.group = group
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self.desiredLength = desiredLength
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}
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@objc
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public func loadedUniqueIds() -> [String] {
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return itemIds
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}
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@objc
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public func contains(uniqueId: String) -> Bool {
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return loadedUniqueIds().contains(uniqueId)
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}
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// This method can be used to extend the desired length
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// and update.
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@objc
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public func update(withDesiredLength desiredLength: UInt, transaction: YapDatabaseReadTransaction) {
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assert(desiredLength >= self.desiredLength)
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self.desiredLength = desiredLength
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update(transaction: transaction)
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}
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// This is the core method of the class. It updates the state to
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// reflect the latest database state & the current desired length.
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@objc
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public func update(transaction: YapDatabaseReadTransaction) {
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AssertIsOnMainThread()
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guard let view = transaction.ext(viewName) as? YapDatabaseAutoViewTransaction else {
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owsFailDebug("Could not load view.")
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return
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}
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guard let group = group else {
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owsFailDebug("No group.")
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return
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}
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// Deserializing interactions is expensive, so we only
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// do that when necessary.
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let sortIdForItemId: (String) -> UInt64? = { (itemId) in
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guard let interaction = TSInteraction.fetch(uniqueId: itemId, transaction: transaction) else {
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owsFailDebug("Could not load interaction.")
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return nil
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}
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return interaction.sortId
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}
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// If we have a "pivot", load all items AFTER the pivot and up to minDesiredLength items BEFORE the pivot.
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// If we do not have a "pivot", load up to minDesiredLength BEFORE the pivot.
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var newItemIds = [ItemId]()
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var canLoadMore = false
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let desiredLength = self.desiredLength
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// Not all items "count" towards the desired length. On an initial load, all items count. Subsequently,
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// only items above the pivot count.
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var afterPivotCount: UInt = 0
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var beforePivotCount: UInt = 0
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// (void (^)(NSString *collection, NSString *key, id object, NSUInteger index, BOOL *stop))block;
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view.enumerateKeys(inGroup: group, with: NSEnumerationOptions.reverse) { (_, key, _, stop) in
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let itemId = key
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// Load "uncounted" items after the pivot if possible.
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//
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// As an optimization, we can skip this check (which requires
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// deserializing the interaction) if beforePivotCount is zero,
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// e.g. we haven't "passed" the pivot yet.
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if beforePivotCount == 0,
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let pivotSortId = self.pivotSortId {
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if let sortId = sortIdForItemId(itemId) {
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let isAfterPivot = sortId > pivotSortId
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if isAfterPivot {
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newItemIds.append(itemId)
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afterPivotCount += 1
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return
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}
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} else {
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owsFailDebug("Could not determine sort id for interaction: \(itemId)")
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}
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}
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// Load "counted" items unless the load window overflows.
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if beforePivotCount >= desiredLength {
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// Overflow
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canLoadMore = true
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stop.pointee = true
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} else {
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newItemIds.append(itemId)
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beforePivotCount += 1
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}
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}
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// The items need to be reversed, since we load them in reverse order.
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self.itemIds = Array(newItemIds.reversed())
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self.canLoadMore = canLoadMore
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self.snapshotOfLastUpdate = transaction.connection.snapshot
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// Establish the pivot, if necessary and possible.
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//
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// Deserializing interactions is expensive. We only need to deserialize
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// interactions that are "after" the pivot. So there would be performance
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// benefits to moving the pivot after each update to the last loaded item.
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//
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// However, this would undesirable side effects. The desired length for
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// conversations with very short disappearing message durations would
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// continuously grow as messages appeared and disappeared.
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//
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// NOTE: if we do end up "moving" the pivot, we also need to increment
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// `self.desiredLength` by `afterPivotCount`.
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if self.pivotSortId == nil {
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if let newLastItemId = newItemIds.first {
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// newItemIds is in reverse order, so its "first" element is actually last.
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if let sortId = sortIdForItemId(newLastItemId) {
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// Update the pivot.
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self.pivotSortId = sortId
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} else {
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owsFailDebug("Could not determine sort id for interaction: \(newLastItemId)")
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}
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}
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}
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}
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// Tries to ensure that the load window includes a given item.
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// On success, returns the index path of that item.
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// On failure, returns nil.
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@objc
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public func ensureLoadWindowContains(uniqueId: String,
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transaction: YapDatabaseReadTransaction) -> IndexPath? {
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if let oldIndex = loadedUniqueIds().firstIndex(of: uniqueId) {
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return IndexPath(row: oldIndex, section: 0)
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}
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guard let view = transaction.ext(viewName) as? YapDatabaseAutoViewTransaction else {
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owsFailDebug("Could not load view.")
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return nil
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}
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guard let group = group else {
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owsFailDebug("No group.")
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return nil
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}
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let indexPtr: UnsafeMutablePointer<UInt> = UnsafeMutablePointer<UInt>.allocate(capacity: 1)
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let wasFound = view.getGroup(nil, index: indexPtr, forKey: uniqueId, inCollection: TSInteraction.collection())
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guard wasFound else {
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owsFailDebug("Could not find interaction.")
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return nil
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}
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let index = indexPtr.pointee
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let threadInteractionCount = view.numberOfItems(inGroup: group)
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guard index < threadInteractionCount else {
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owsFailDebug("Invalid index.")
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return nil
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}
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// This math doesn't take into account the number of items loaded _after_ the pivot.
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// That's fine; it's okay to load too many interactions here.
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let desiredWindowSize: UInt = threadInteractionCount - index
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self.update(withDesiredLength: desiredWindowSize, transaction: transaction)
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guard let newIndex = loadedUniqueIds().firstIndex(of: uniqueId) else {
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owsFailDebug("Couldn't find interaction.")
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return nil
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}
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return IndexPath(row: newIndex, section: 0)
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}
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@objc
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public class ConversationMessageMappingDiff: NSObject {
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@objc
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public let addedItemIds: Set<String>
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@objc
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public let removedItemIds: Set<String>
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@objc
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public let updatedItemIds: Set<String>
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init(addedItemIds: Set<String>, removedItemIds: Set<String>, updatedItemIds: Set<String>) {
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self.addedItemIds = addedItemIds
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self.removedItemIds = removedItemIds
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self.updatedItemIds = updatedItemIds
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}
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}
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// Updates and then calculates which items were inserted, removed or modified.
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@objc
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public func updateAndCalculateDiff(transaction: YapDatabaseReadTransaction,
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notifications: [NSNotification]) -> ConversationMessageMappingDiff? {
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let oldItemIds = Set(self.itemIds)
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self.update(transaction: transaction)
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let newItemIds = Set(self.itemIds)
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let removedItemIds = oldItemIds.subtracting(newItemIds)
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let addedItemIds = newItemIds.subtracting(oldItemIds)
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// We only notify for updated items that a) were previously loaded b) weren't also inserted or removed.
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let updatedItemIds = (self.updatedItemIds(for: notifications)
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.subtracting(addedItemIds)
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.subtracting(removedItemIds)
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.intersection(oldItemIds))
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return ConversationMessageMappingDiff(addedItemIds: addedItemIds,
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removedItemIds: removedItemIds,
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updatedItemIds: updatedItemIds)
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}
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// For performance reasons, the database modification notifications are used
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// to determine which items were modified. If YapDatabase ever changes the
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// structure or semantics of these notifications, we'll need to update this
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// code to reflect that.
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private func updatedItemIds(for notifications: [NSNotification]) -> Set<String> {
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var updatedItemIds = Set<String>()
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for notification in notifications {
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// Unpack the YDB notification, looking for row changes.
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guard let userInfo =
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notification.userInfo else {
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owsFailDebug("Missing userInfo.")
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continue
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}
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guard let viewChangesets =
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userInfo[YapDatabaseExtensionsKey] as? NSDictionary else {
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// No changes for any views, skip.
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continue
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}
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guard let changeset =
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viewChangesets[viewName] as? NSDictionary else {
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// No changes for this view, skip.
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continue
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}
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// This constant matches a private constant in YDB.
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let changeset_key_changes: String = "changes"
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guard let changesetChanges = changeset[changeset_key_changes] as? [Any] else {
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owsFailDebug("Missing changeset changes.")
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continue
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}
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for change in changesetChanges {
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if change as? YapDatabaseViewSectionChange != nil {
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// Ignore.
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} else if let rowChange = change as? YapDatabaseViewRowChange {
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updatedItemIds.insert(rowChange.collectionKey.key)
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} else {
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owsFailDebug("Invalid change: \(type(of: change)).")
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continue
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}
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}
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}
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return updatedItemIds
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}
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}
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