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268// Created by Laura Skelton on 11/25/16.
// Copyright © 2016 Airbnb. All rights reserved.
// MARK: - Collection
extension Collection where Element: Diffable, Index == Int {
/// Diffs two collections (e.g. `Array`s) of `Diffable` items, returning an `IndexChangeset`
/// representing the minimal set of changes to get from the other collection to this collection.
///
/// - Parameters:
/// - from other: The collection of old data.
func makeChangeset(from other: Self) -> IndexChangeset {
// Arranging the elements contiguously prior to diffing improves performance by ~40%.
let new = ContiguousArray(self)
let old = ContiguousArray(other)
/// The entries in both this and the other collection, keyed by their `dataID`s.
var entries = [AnyHashable: EpoxyEntry](minimumCapacity: new.count)
var duplicates = [EpoxyEntry]()
var newResults = ContiguousArray<NewRecord>()
newResults.reserveCapacity(new.count)
for index in new.indices {
let id = new[index].diffIdentifier
let entry = entries[id, default: EpoxyEntry()]
if entry.trackNewIndex(index) {
duplicates.append(entry)
}
entries[id] = entry
newResults.append(NewRecord(entry: entry))
}
var oldResults = ContiguousArray<OldRecord>()
oldResults.reserveCapacity(old.count)
for index in old.indices {
let id = old[index].diffIdentifier
let entry = entries[id]
entry?.pushOldIndex(index)
oldResults.append(OldRecord(entry: entry))
}
for newIndex in new.indices {
let entry = newResults[newIndex].entry
if let oldIndex = entry.popOldIndex() {
let newItem = new[newIndex]
let oldItem = other[oldIndex]
if !oldItem.isDiffableItemEqual(to: newItem) {
entry.isUpdated = true
}
newResults[newIndex].correspondingOldIndex = oldIndex
oldResults[oldIndex].correspondingNewIndex = newIndex
}
}
var deletes = [Int]()
var deleteOffsets = [Int]()
deleteOffsets.reserveCapacity(old.count)
var runningDeleteOffset = 0
for index in old.indices {
deleteOffsets.append(runningDeleteOffset)
let record = oldResults[index]
if record.correspondingNewIndex == nil {
deletes.append(index)
runningDeleteOffset += 1
}
}
var inserts = [Int]()
var updates = [(Int, Int)]()
var moves = [(Int, Int)]()
var insertOffsets = [Int]()
insertOffsets.reserveCapacity(new.count)
var runningInsertOffset = 0
for index in new.indices {
insertOffsets.append(runningInsertOffset)
let record = newResults[index]
if let oldArrayIndex = record.correspondingOldIndex {
if record.entry.isUpdated {
updates.append((oldArrayIndex, index))
}
let insertOffset = insertOffsets[index]
let deleteOffset = deleteOffsets[oldArrayIndex]
if (oldArrayIndex - deleteOffset + insertOffset) != index {
moves.append((oldArrayIndex, index))
}
} else {
inserts.append(index)
runningInsertOffset += 1
}
}
EpoxyLogger.shared.assert(
old.count + inserts.count - deletes.count == new.count,
"Failed sanity check for old count with changes matching new count."
)
return IndexChangeset(
inserts: inserts,
deletes: deletes,
updates: updates,
moves: moves,
newIndices: oldResults.map { $0.correspondingNewIndex },
duplicates: duplicates.map { $0.newIndices }
)
}
/// Diffs between two collections (eg. `Array`s) of `Diffable` items, and returns an `IndexPathChangeset`
/// representing the minimal set of changes to get from the other collection to this collection.
///
/// - Parameters:
/// - from other: The collection of old data.
/// - fromSection: The section the other collection's data exists within. Defaults to `0`.
/// - toSection: The section this collection's data exists within. Defaults to `0`.
func makeIndexPathChangeset(
from other: Self,
fromSection: Int = 0,
toSection: Int = 0
) -> IndexPathChangeset {
let indexChangeset = makeChangeset(from: other)
return IndexPathChangeset(
inserts: indexChangeset.inserts.map { index in
[toSection, index]
},
deletes: indexChangeset.deletes.map { index in
[fromSection, index]
},
updates: indexChangeset.updates.map { fromIndex, toIndex in
([fromSection, fromIndex], [toSection, toIndex])
},
moves: indexChangeset.moves.map { fromIndex, toIndex in
([fromSection, fromIndex], [toSection, toIndex])
},
duplicates: indexChangeset.duplicates.map { duplicate in
duplicate.map { index in
[toSection, index]
}
}
)
}
/// Diffs between two collections (e.g. `Array`s) of `Diffable` items, returning an
/// `IndexSetChangeset` representing the minimal set of changes to get from the other collection
/// to this collection.
///
/// - Parameters:
/// - from other: The collection of old data.
func makeIndexSetChangeset(from other: Self) -> IndexSetChangeset {
let indexChangeset = makeChangeset(from: other)
return IndexSetChangeset(
inserts: .init(indexChangeset.inserts),
deletes: .init(indexChangeset.deletes),
updates: indexChangeset.updates,
moves: indexChangeset.moves,
newIndices: indexChangeset.newIndices,
duplicates: indexChangeset.duplicates.map { .init($0) }
)
}
}
extension Collection where Element: DiffableSection, Index == Int {
/// Diffs between two collections (e.g. `Array`s) of `DiffableSection` items, returning an
/// `SectionedChangeset` representing the minimal set of changes to get from the other collection
/// to this collection.
///
/// - Parameters:
/// - from other: The collection of old data.
func makeSectionedChangeset(from other: Self) -> SectionedChangeset {
let sectionChangeset = makeIndexSetChangeset(from: other)
var itemChangeset = IndexPathChangeset()
for fromSectionIndex in other.indices {
guard let toSectionIndex = sectionChangeset.newIndices[fromSectionIndex] else {
continue
}
let fromItems = other[fromSectionIndex].diffableItems
let toItems = self[toSectionIndex].diffableItems
let itemIndexChangeset = toItems.makeIndexPathChangeset(
from: fromItems,
fromSection: fromSectionIndex,
toSection: toSectionIndex
)
itemChangeset += itemIndexChangeset
}
return SectionedChangeset(sectionChangeset: sectionChangeset, itemChangeset: itemChangeset)
}
}
// MARK: - EpoxyEntry
/// A bookkeeping reference type for the diffing algorithm.
private final class EpoxyEntry {
// MARK: Internal
private(set) var oldIndices = [Int]()
private(set) var newIndices = [Int]()
var isUpdated = false
/// Tracks an index from the new indices, returning `true` if this entry has previously tracked
/// a new index as a means to identify duplicates and `false` otherwise.
func trackNewIndex(_ index: Int) -> Bool {
let previouslyEmpty = newIndices.isEmpty
newIndices.append(index)
// We've encountered a duplicate, return true so we can track it.
if !previouslyEmpty, newIndices.count == 2 {
return true
}
return false
}
func pushOldIndex(_ index: Int) {
oldIndices.append(index)
}
func popOldIndex() -> Int? {
guard currentOldIndex < oldIndices.endIndex else {
return nil
}
defer {
currentOldIndex += 1
}
return oldIndices[currentOldIndex]
}
// MARK: Private
private var currentOldIndex = 0
}
// MARK: - OldRecord
/// A bookkeeping type for pairing up an old element with its new index.
private struct OldRecord {
var entry: EpoxyEntry?
var correspondingNewIndex: Int? = nil
}
// MARK: - NewRecord
/// A bookkeeping type for pairing up a new element with its old index.
private struct NewRecord {
var entry: EpoxyEntry
var correspondingOldIndex: Int? = nil
}