Switch asset picker to use diffable data sources

Tusker/Screens/Asset Picker/AssetCollectionViewController.swift

@@ -22,20 +22,22 @@ class AssetCollectionViewController: UICollectionViewController {
 
     weak var delegate: AssetCollectionViewControllerDelegate?
     
-    var flowLayout: UICollectionViewFlowLayout {
+    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
+    private var flowLayout: UICollectionViewFlowLayout {
         return collectionViewLayout as! UICollectionViewFlowLayout
     }
     
-    var availableWidth: CGFloat!
+    private var availableWidth: CGFloat!
-    var thumbnailSize: CGSize!
+    private var thumbnailSize: CGSize!
     
-    let imageManager = PHCachingImageManager()
+    private let imageManager = PHCachingImageManager()
-    var fetchResult: PHFetchResult<PHAsset>!
+    private var fetchResult: PHFetchResult<PHAsset>!
     
     var selectedAssets: [PHAsset] {
-        return collectionView.indexPathsForSelectedItems?.map({ (indexPath) in
+        return collectionView.indexPathsForSelectedItems?.compactMap { (indexPath) in
-            fetchResult.object(at: indexPath.row - 1)
+            guard case let .asset(asset) = dataSource.itemIdentifier(for: indexPath) else { return nil }
-        }) ?? []
+            return asset
+        } ?? []
     }
     
     init() {
@@ -71,14 +73,42 @@ class AssetCollectionViewController: UICollectionViewController {
         collectionView.register(UINib(nibName: "AssetCollectionViewCell", bundle: .main), forCellWithReuseIdentifier: reuseIdentifier)
         collectionView.register(UINib(nibName: "ShowCameraCollectionViewCell", bundle: .main), forCellWithReuseIdentifier: cameraReuseIdentifier)
         
+        dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: collectionView, cellProvider: { (collectionView, indexPath, item) -> UICollectionViewCell? in
+            switch item {
+            case .showCamera:
+                return collectionView.dequeueReusableCell(withReuseIdentifier: cameraReuseIdentifier, for: indexPath)
+            case let .asset(asset):
+                let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! AssetCollectionViewCell
+        
+                cell.updateUI(asset: asset)
+                self.imageManager.requestImage(for: asset, targetSize: self.thumbnailSize, contentMode: .aspectFill, options: nil) { (image, _) in
+                    guard let image = image else { return }
+                    DispatchQueue.main.async {
+                        guard cell.assetIdentifier == asset.localIdentifier else { return }
+                        cell.thumbnailImage = image
+                    }
+                }
+
+                return cell
+            }
+        })
+        
         let options = PHFetchOptions()
         options.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
         fetchResult = fetchAssets(with: options)
+        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
+        snapshot.appendSections([.assets])
+        var items: [Item] = [.showCamera]
+        fetchResult.enumerateObjects { (asset, _, _) in
+            items.append(.asset(asset))
+        }
+        snapshot.appendItems(items)
+        dataSource.apply(snapshot, animatingDifferences: false)
         
         collectionView.allowsMultipleSelection = true
         setEditing(true, animated: false)
         
-        updateItemsSelected()
+        updateItemsSelectedCount()
 
         if let singleFingerPanGesture = collectionView.gestureRecognizers?.first(where: {
                 $0.name == "multi-select.singleFingerPanGesture"
@@ -115,43 +145,12 @@ class AssetCollectionViewController: UICollectionViewController {
         return PHAsset.fetchAssets(with: options)
     }
     
-    func updateItemsSelected() {
+    func updateItemsSelectedCount() {
         let selected = collectionView.indexPathsForSelectedItems?.count ?? 0
         
         navigationItem.title = "\(selected) selected"
     }
 
-    // MARK: UICollectionViewDataSource
-
-    override func numberOfSections(in collectionView: UICollectionView) -> Int {
-        return 1
-    }
-
-    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
-        return fetchResult.count + 1
-    }
-
-    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
-        if indexPath.row == 0 {
-            return collectionView.dequeueReusableCell(withReuseIdentifier: cameraReuseIdentifier, for: indexPath)
-        } else {
-            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! AssetCollectionViewCell
-    
-            let asset = fetchResult.object(at: indexPath.row - 1)
-    
-            cell.updateUI(asset: asset)
-            imageManager.requestImage(for: asset, targetSize: thumbnailSize, contentMode: .aspectFill, options: nil) { (image, _) in
-                guard let image = image else { return }
-                DispatchQueue.main.async {
-                    guard cell.assetIdentifier == asset.localIdentifier else { return }
-                    cell.thumbnailImage = image
-                }
-            }
-
-            return cell
-        }
-    }
-
     // MARK: UICollectionViewDelegate
 
     override func collectionView(_ collectionView: UICollectionView, shouldBeginMultipleSelectionInteractionAt indexPath: IndexPath) -> Bool {
@@ -159,37 +158,35 @@ class AssetCollectionViewController: UICollectionViewController {
     }
     
     override func collectionView(_ collectionView: UICollectionView, shouldSelectItemAt indexPath: IndexPath) -> Bool {
-        if indexPath.row > 0,
+        guard let item = dataSource.itemIdentifier(for: indexPath) else { return false }
-            let delegate = delegate {
+        if let delegate = delegate,
-            let asset = fetchResult.object(at: indexPath.row - 1)
+           case let .asset(asset) = item {
             return delegate.shouldSelectAsset(asset)
         }
         return true
     }
     
     override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
-        if indexPath.row == 0 {
+        guard let item = dataSource.itemIdentifier(for: indexPath) else { return }
+        switch item {
+        case .showCamera:
             collectionView.deselectItem(at: indexPath, animated: false)
             delegate?.captureFromCamera()
-        } else {
+        case .asset(_):
-            updateItemsSelected()
+            updateItemsSelectedCount()
         }
     }
     
     override func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
-        updateItemsSelected()
+        updateItemsSelectedCount()
     }
     
     override func collectionView(_ collectionView: UICollectionView, contextMenuConfigurationForItemAt indexPath: IndexPath, point: CGPoint) -> UIContextMenuConfiguration? {
-        if indexPath.row == 0 {
+        guard case let .asset(asset) = dataSource.itemIdentifier(for: indexPath) else { return nil }
-            return nil
-        } else {
-            let asset = fetchResult.object(at: indexPath.row - 1)
         return UIContextMenuConfiguration(identifier: indexPath as NSIndexPath, previewProvider: { () -> UIViewController? in
             return AssetPreviewViewController(asset: asset)
         }, actionProvider: nil)
     }
-    }
     
     override func collectionView(_ collectionView: UICollectionView, previewForHighlightingContextMenuWithConfiguration configuration: UIContextMenuConfiguration) -> UITargetedPreview? {
         if let indexPath = (configuration.identifier as? NSIndexPath) as IndexPath?,
@@ -210,3 +207,13 @@ class AssetCollectionViewController: UICollectionViewController {
     }
     
 }
+
+extension AssetCollectionViewController {
+    enum Section: Hashable {
+        case assets
+    }
+    enum Item: Hashable {
+        case showCamera
+        case asset(PHAsset)
+    }
+}