Initial commit

Sources/AppKit/CocoaCollectionViewDiffableDataSource.swift

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+#if os(macOS)
+
+import AppKit
+import DifferenceKit
+
+/// A class for backporting `NSCollectionViewDiffableDataSource` introduced in macOS 10.15+.
+/// Represents the data model object for `NSCollectionView` that can be applies the
+/// changes with automatic diffing.
+open class CocoaCollectionViewDiffableDataSource<SectionIdentifierType: Hashable, ItemIdentifierType: Hashable>: NSObject, NSCollectionViewDataSource {
+    /// The type of closure providing the item.
+    public typealias ItemProvider = (NSCollectionView, IndexPath, ItemIdentifierType) -> NSCollectionViewItem?
+
+    private weak var collectionView: NSCollectionView?
+    private let itemProvider: ItemProvider
+    private let core = DiffableDataSourceCore<SectionIdentifierType, ItemIdentifierType>()
+
+    /// Creates a new data source.
+    ///
+    /// - Parameters:
+    ///   - collectionView: A collection view instance to be managed.
+    ///   - itemProvider: A closure to make the item.
+    public init(collectionView: NSCollectionView, itemProvider: @escaping ItemProvider) {
+        self.collectionView = collectionView
+        self.itemProvider = itemProvider
+        super.init()
+
+        collectionView.dataSource = self
+    }
+
+    /// Applies given snapshot to perform automatic diffing update.
+    ///
+    /// - Parameters:
+    ///   - snapshot: A snapshot object to be applied to data model.
+    ///   - animatingDifferences: A Boolean value indicating whether to update with
+    ///                           diffing animation.
+    public func apply(_ snapshot: DiffableDataSourceSnapshot<SectionIdentifierType, ItemIdentifierType>, animatingDifferences: Bool = true) {
+        core.apply(
+            snapshot,
+            view: collectionView,
+            animatingDifferences: animatingDifferences,
+            performUpdates: { collectionView, changeset, setSections in
+                collectionView.reload(using: changeset, setData: setSections)
+        })
+    }
+
+    /// Returns a new snapshot object of current state.
+    ///
+    /// - Returns: A new snapshot object of current state.
+    public func snapshot() -> DiffableDataSourceSnapshot<SectionIdentifierType, ItemIdentifierType> {
+        return core.snapshot()
+    }
+
+    /// Returns an item identifier for given index path.
+    ///
+    /// - Parameters:
+    ///   - indexPath: An index path for the item identifier.
+    ///
+    /// - Returns: An item identifier for given index path.
+    public func itemIdentifier(for indexPath: IndexPath) -> ItemIdentifierType? {
+        return core.itemIdentifier(for: indexPath)
+    }
+
+    /// Returns an index path for given item identifier.
+    ///
+    /// - Parameters:
+    ///   - itemIdentifier: An identifier of item.
+    ///
+    /// - Returns: An index path for given item identifier.
+    public func indexPath(for itemIdentifier: ItemIdentifierType) -> IndexPath? {
+        return core.indexPath(for: itemIdentifier)
+    }
+
+    /// Returns the number of sections in the data source.
+    ///
+    /// - Parameters:
+    ///   - collectionView: A collection view instance managed by `self`.
+    ///
+    /// - Returns: The number of sections in the data source.
+    public func numberOfSections(in collectionView: NSCollectionView) -> Int {
+        return core.numberOfSections()
+    }
+
+    /// Returns the number of items in the specified section.
+    ///
+    /// - Parameters:
+    ///   - collectionView: A collection view instance managed by `self`.
+    ///   - section: An index of section.
+    ///
+    /// - Returns: The number of items in the specified section.
+    public func collectionView(_ collectionView: NSCollectionView, numberOfItemsInSection section: Int) -> Int {
+        return core.numberOfItems(inSection: section)
+    }
+
+    /// Returns an item at specified index path.
+    ///
+    /// - Parameters:
+    ///   - collectionView: A collection view instance managed by `self`.
+    ///   - indexPath: An index path for item.
+    ///
+    /// - Returns: An item at specified index path.
+    open func collectionView(_ collectionView: NSCollectionView, itemForRepresentedObjectAt indexPath: IndexPath) -> NSCollectionViewItem {
+        let itemIdentifier = core.unsafeItemIdentifier(for: indexPath)
+        guard let item = itemProvider(collectionView, indexPath, itemIdentifier) else {
+            universalError("NSCollectionView dataSource returned a nil item at index path: \(indexPath), collectionView: \(collectionView), itemIdentifier: \(itemIdentifier)")
+        }
+
+        return item
+    }
+}
+
+#endif