Sync and show items

Fervor/Feed.swift

@@ -10,7 +10,7 @@ import Foundation
 public struct Feed: Decodable {
     public let id: FervorID
     public let title: String
-    public let url: URL
+    public let url: URL?
     public let serviceURL: URL?
     public let feedURL: URL
     public let lastUpdated: Date
@@ -21,7 +21,7 @@ public struct Feed: Decodable {
         
         self.id = try container.decode(FervorID.self, forKey: .id)
         self.title = try container.decode(String.self, forKey: .title)
-        self.url = try container.decode(URL.self, forKey: .url)
+        self.url = try container.decode(URL?.self, forKey: .url)
         self.serviceURL = try container.decodeIfPresent(URL.self, forKey: .serviceURL)
         self.feedURL = try container.decode(URL.self, forKey: .feedURL)
         self.lastUpdated = try container.decode(Date.self, forKey: .lastUpdated)

Fervor/FervorClient.swift

@@ -15,7 +15,22 @@ public class FervorClient {
     
     private let decoder: JSONDecoder = {
         let d = JSONDecoder()
-        d.dateDecodingStrategy = .iso8601
+        let withFractionalSeconds = ISO8601DateFormatter()
+        withFractionalSeconds.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
+        let without = ISO8601DateFormatter()
+        without.formatOptions = [.withInternetDateTime]
+        // because fucking ISO8601DateFormatter isn't a DateFormatter
+        d.dateDecodingStrategy = .custom({ decoder in
+            let s = try decoder.singleValueContainer().decode(String.self)
+            // try both because Elixir's DateTime.to_iso8601 omits the .0 if the date doesn't have fractional seconds
+            if let d = withFractionalSeconds.date(from: s) {
+                return d
+            } else if let d = without.date(from: s) {
+                return d
+            } else {
+                throw DateDecodingError()
+            }
+        })
         return d
     }()
     
@@ -25,9 +40,10 @@ public class FervorClient {
         self.session = session
     }
     
-    private func buildURL(path: String) -> URL {
+    private func buildURL(path: String, queryItems: [URLQueryItem] = []) -> URL {
         var components = URLComponents(url: instanceURL, resolvingAgainstBaseURL: false)!
         components.path = path
+        components.queryItems = queryItems
         return components.url!
     }
     
@@ -36,7 +52,10 @@ public class FervorClient {
         if let accessToken = accessToken {
             request.addValue("Bearer \(accessToken)", forHTTPHeaderField: "Authorization")
         }
-        let (data, _) = try await session.data(for: request, delegate: nil)
+        let (data, response) = try await session.data(for: request, delegate: nil)
+        if (response as! HTTPURLResponse).statusCode == 404 {
+            throw Error.notFound
+        }
         let decoded = try decoder.decode(T.self, from: data)
         return decoded
     }
@@ -75,6 +94,31 @@ public class FervorClient {
         return try await performRequest(request)
     }
     
+    public func syncItems(lastSync: Date?) async throws -> ItemsSyncUpdate {
+        let request = URLRequest(url: buildURL(path: "/api/v1/items/sync", queryItems: [
+            URLQueryItem(name: "last_sync", value: lastSync?.formatted(.iso8601))
+        ]))
+        return try await performRequest(request)
+    }
+    
+    public func items(feed id: FervorID) async throws -> [Item] {
+        let request = URLRequest(url: buildURL(path: "/api/v1/feeds/\(id)/items"))
+        return try await performRequest(request)
+    }
+    
+    public func item(id: FervorID) async throws -> Item? {
+        let request = URLRequest(url: buildURL(path: "/api/v1/items/\(id)"))
+        do {
+            return try await performRequest(request)
+        } catch {
+            if let error = error as? Error, case .notFound = error {
+                return nil
+            } else {
+                throw error
+            }
+        }
+    }
+    
     public struct Auth {
         public let accessToken: String
         public let refreshToken: String?
@@ -83,6 +127,11 @@ public class FervorClient {
     public enum Error: Swift.Error {
         case urlSession(Swift.Error)
         case decode(Swift.Error)
+        case notFound
     }
     
 }
+
+private struct DateDecodingError: Error {
+    
+}

Fervor/Item.swift

@@ -8,17 +8,17 @@
 import Foundation
 
 public struct Item: Decodable {
-    let id: FervorID
+    public let id: FervorID
-    let feedID: FervorID
+    public let feedID: FervorID
-    let title: String
+    public let title: String
-    let author: String
+    public let author: String
-    let published: Date?
+    public let published: Date?
-    let createdAt: Date?
+    public let createdAt: Date?
-    let content: String?
+    public let content: String?
-    let summary: String?
+    public let summary: String?
-    let url: URL
+    public let url: URL
-    let serviceURL: URL?
+    public let serviceURL: URL?
-    let read: Bool?
+    public let read: Bool?
     
     public init(from decoder: Decoder) throws {
         let container = try decoder.container(keyedBy: CodingKeys.self)

Fervor/ItemsSyncUpdate.swift

@@ -0,0 +1,30 @@
+//
+//  ItemsSyncUpdate.swift
+//  Fervor
+//
+//  Created by Shadowfacts on 1/9/22.
+//
+
+import Foundation
+
+public struct ItemsSyncUpdate: Decodable {
+    
+    public let syncTimestamp: Date
+    public let delete: [FervorID]
+    public let upsert: [Item]
+    
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+        
+        self.syncTimestamp = try container.decode(Date.self, forKey: .syncTimestamp)
+        self.delete = try container.decode([FervorID].self, forKey: .delete)
+        self.upsert = try container.decode([Item].self, forKey: .upsert)
+    }
+    
+    private enum CodingKeys: String, CodingKey {
+        case syncTimestamp = "sync_timestamp"
+        case delete
+        case upsert
+    }
+    
+}

Reader.xcodeproj/project.pbxproj

@@ -33,6 +33,9 @@
 		D6C68834272CD44900874C10 /* Fervor.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6C68833272CD44900874C10 /* Fervor.swift */; };
 		D6C68856272CD7C600874C10 /* Item.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6C68855272CD7C600874C10 /* Item.swift */; };
 		D6C68858272CD8CD00874C10 /* Group.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6C68857272CD8CD00874C10 /* Group.swift */; };
+		D6E2434C278B456A0005E546 /* ItemsViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6E2434B278B456A0005E546 /* ItemsViewController.swift */; };
+		D6E24350278B62F60005E546 /* Item.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6E2434F278B62F60005E546 /* Item.swift */; };
+		D6E24352278B6DF90005E546 /* ItemsSyncUpdate.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6E24351278B6DF90005E546 /* ItemsSyncUpdate.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -103,6 +106,9 @@
 		D6C68833272CD44900874C10 /* Fervor.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Fervor.swift; sourceTree = "<group>"; };
 		D6C68855272CD7C600874C10 /* Item.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Item.swift; sourceTree = "<group>"; };
 		D6C68857272CD8CD00874C10 /* Group.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Group.swift; sourceTree = "<group>"; };
+		D6E2434B278B456A0005E546 /* ItemsViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ItemsViewController.swift; sourceTree = "<group>"; };
+		D6E2434F278B62F60005E546 /* Item.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Item.swift; sourceTree = "<group>"; };
+		D6E24351278B6DF90005E546 /* ItemsSyncUpdate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ItemsSyncUpdate.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -143,6 +149,7 @@
 			children = (
 				D65B18BF2750533E004A9448 /* Home */,
 				D65B18B027504691004A9448 /* Login */,
+				D6E2434A278B455C0005E546 /* Items */,
 			);
 			path = Screens;
 			sourceTree = "<group>";
@@ -207,6 +214,7 @@
 				D6C687F9272CD27700874C10 /* LaunchScreen.storyboard */,
 				D6C687FC272CD27700874C10 /* Info.plist */,
 				D6C687F4272CD27600874C10 /* Reader.xcdatamodeld */,
+				D6E2434F278B62F60005E546 /* Item.swift */,
 			);
 			path = Reader;
 			sourceTree = "<group>";
@@ -240,11 +248,20 @@
 				D6C68857272CD8CD00874C10 /* Group.swift */,
 				D6C6882F272CD2CF00874C10 /* Instance.swift */,
 				D6C68855272CD7C600874C10 /* Item.swift */,
+				D6E24351278B6DF90005E546 /* ItemsSyncUpdate.swift */,
 				D65B18BB27504FE7004A9448 /* Token.swift */,
 			);
 			path = Fervor;
 			sourceTree = "<group>";
 		};
+		D6E2434A278B455C0005E546 /* Items */ = {
+			isa = PBXGroup;
+			children = (
+				D6E2434B278B456A0005E546 /* ItemsViewController.swift */,
+			);
+			path = Items;
+			sourceTree = "<group>";
+		};
 /* End PBXGroup section */
 
 /* Begin PBXHeadersBuildPhase section */
@@ -423,6 +440,8 @@
 				D6C687EC272CD27600874C10 /* AppDelegate.swift in Sources */,
 				D6C687F6272CD27600874C10 /* Reader.xcdatamodeld in Sources */,
 				D6A8A33727766EA100CCEC72 /* ManagedObjectExtensions.swift in Sources */,
+				D6E2434C278B456A0005E546 /* ItemsViewController.swift in Sources */,
+				D6E24350278B62F60005E546 /* Item.swift in Sources */,
 				D65B18BE275051A1004A9448 /* LocalData.swift in Sources */,
 				D65B18B22750469D004A9448 /* LoginViewController.swift in Sources */,
 				D65B18C127505348004A9448 /* HomeViewController.swift in Sources */,
@@ -454,6 +473,7 @@
 				D65B18BC27504FE7004A9448 /* Token.swift in Sources */,
 				D6C68856272CD7C600874C10 /* Item.swift in Sources */,
 				D6C68830272CD2CF00874C10 /* Instance.swift in Sources */,
+				D6E24352278B6DF90005E546 /* ItemsSyncUpdate.swift in Sources */,
 				D6C68832272CD40600874C10 /* Feed.swift in Sources */,
 				D6C68858272CD8CD00874C10 /* Group.swift in Sources */,
 				D6C68834272CD44900874C10 /* Fervor.swift in Sources */,

Reader/CoreData/ManagedObjectExtensions.swift

@@ -36,3 +36,23 @@ extension Feed {
     }
     
 }
+
+extension Item {
+    
+    func updateFromServer(_ serverItem: Fervor.Item) {
+        guard self.id == nil || self.id == serverItem.id else { return }
+        self.id = serverItem.id
+        self.author = serverItem.author
+        self.content = serverItem.content
+        self.title = serverItem.title
+        self.read = serverItem.read ?? false
+        self.published = serverItem.published
+        self.url = serverItem.url
+        if self.feed?.id != serverItem.feedID {
+            let feedReq = Feed.fetchRequest()
+            feedReq.predicate = NSPredicate(format: "id = %@", serverItem.feedID)
+            self.feed = try! self.managedObjectContext!.fetch(feedReq).first!
+        }
+    }
+    
+}

Reader/CoreData/PersistentContainer.swift

@@ -7,6 +7,7 @@
 
 import CoreData
 import Fervor
+import OSLog
 
 class PersistentContainer: NSPersistentContainer {
     
@@ -22,7 +23,13 @@ class PersistentContainer: NSPersistentContainer {
         return context
     }()
     
-    init(account: LocalData.Account) {
+    private weak var fervorController: FervorController?
+    
+    private let logger = Logger(subsystem: Bundle.main.bundleIdentifier!, category: "PersistentContainer")
+    
+    init(account: LocalData.Account, fervorController: FervorController) {
+        self.fervorController = fervorController
+        
         super.init(name: "\(account.id)", managedObjectModel: PersistentContainer.managedObjectModel)
         
         loadPersistentStores { description, error in
@@ -32,6 +39,27 @@ class PersistentContainer: NSPersistentContainer {
         }
     }
     
+    func lastSyncDate() async throws -> Date? {
+        return try await backgroundContext.perform {
+            let state = try self.backgroundContext.fetch(SyncState.fetchRequest()).first
+            return state?.lastSync
+        }
+    }
+    
+    func updateLastSyncDate(_ date: Date) async throws {
+        try await backgroundContext.perform {
+            if let state = try self.backgroundContext.fetch(SyncState.fetchRequest()).first {
+                state.lastSync = date
+            } else {
+                let state = SyncState(context: self.backgroundContext)
+                state.lastSync = date
+            }
+            
+            try self.backgroundContext.save()
+            try self.viewContext.save()
+        }
+    }
+    
     func sync(serverGroups: [Fervor.Group], serverFeeds: [Fervor.Feed]) async throws {
         try await backgroundContext.perform {
             let existingGroups = try self.backgroundContext.fetch(Group.fetchRequest())
@@ -64,4 +92,40 @@ class PersistentContainer: NSPersistentContainer {
         }
     }
     
+    func syncItems(_ syncUpdate: ItemsSyncUpdate) async throws {
+        try await backgroundContext.perform {
+            self.logger.debug("syncItems: deleting \(syncUpdate.delete.count, privacy: .public) items")
+            let deleteReq = Item.fetchRequest()
+            deleteReq.predicate = NSPredicate(format: "id in %@", syncUpdate.delete)
+            let delete = NSBatchDeleteRequest(fetchRequest: deleteReq as! NSFetchRequest<NSFetchRequestResult>)
+            delete.resultType = .resultTypeObjectIDs
+            let result = try self.backgroundContext.execute(delete)
+            
+            if let deleteResult = result as? NSBatchDeleteResult,
+               let objectIDs = deleteResult.result as? [NSManagedObjectID] {
+                NSManagedObjectContext.mergeChanges(fromRemoteContextSave: [NSDeletedObjectsKey: objectIDs], into: [self.backgroundContext])
+                // todo: does the background/view contexts need to get saved then?
+            }
+            
+            let req = Item.fetchRequest()
+            req.predicate = NSPredicate(format: "id in %@", syncUpdate.upsert.map(\.id))
+            let existing = try self.backgroundContext.fetch(req)
+            self.logger.debug("syncItems: updating \(existing.count, privacy: .public) items, inserting \(syncUpdate.upsert.count - existing.count, privacy: .public)")
+            // todo: this feels like it'll be slow when there are many items
+            for item in syncUpdate.upsert {
+                if let existing = existing.first(where: { $0.id == item.id }) {
+                    existing.updateFromServer(item)
+                } else {
+                    let mo = Item(context: self.backgroundContext)
+                    mo.updateFromServer(item)
+                }
+            }
+            
+            if self.backgroundContext.hasChanges {
+                try self.backgroundContext.save()
+                try self.viewContext.save()
+            }
+        }
+    }
+    
 }

Reader/FervorController.swift

@@ -7,6 +7,7 @@
 
 import Foundation
 import Fervor
+import OSLog
 
 class FervorController {
     
@@ -14,7 +15,9 @@ class FervorController {
     
     let instanceURL: URL
     
-    private let client: FervorClient
+    private let logger = Logger(subsystem: Bundle.main.bundleIdentifier!, category: "FervorController")
+    
+    let client: FervorClient
     private(set) var clientID: String?
     private(set) var clientSecret: String?
     private(set) var accessToken: String?
@@ -34,7 +37,7 @@ class FervorController {
         
         self.client.accessToken = account.accessToken
         
-        self.persistentContainer = PersistentContainer(account: account)
+        self.persistentContainer = PersistentContainer(account: account, fervorController: self)
     }
     
     func register() async throws -> ClientRegistration {
@@ -50,10 +53,17 @@ class FervorController {
         accessToken = token.accessToken
     }
     
-    func syncGroupsAndFeeds() async {
+    func syncAll() async {
+        logger.info("Syncing groups and feeds")
         async let groups = try! client.groups()
         async let feeds = try! client.feeds()
         try! await persistentContainer.sync(serverGroups: groups, serverFeeds: feeds)
+        
+        let lastSync = try! await persistentContainer.lastSyncDate()
+        logger.info("Syncing items with last sync date: \(String(describing: lastSync), privacy: .public)")
+        let update = try! await client.syncItems(lastSync: lastSync)
+        try! await persistentContainer.syncItems(update)
+        try! await persistentContainer.updateLastSyncDate(update.syncTimestamp)
     }
     
 }

Reader/Item.swift

@@ -0,0 +1,27 @@
+//
+//  Item.swift
+//  Reader
+//
+//  Created by Shadowfacts on 1/9/22.
+//
+
+import CoreData
+
+@objc(Item)
+public final class Item: NSManagedObject {
+    
+    @nonobjc public class func fetchRequest() -> NSFetchRequest<Item> {
+        return NSFetchRequest<Item>(entityName: "Item")
+    }
+    
+    @NSManaged public var author: String?
+    @NSManaged public var content: String?
+    @NSManaged public var id: String?
+    @NSManaged public var title: String?
+    @NSManaged public var read: Bool
+    @NSManaged public var published: Date?
+    @NSManaged public var url: URL?
+    
+    @NSManaged public var feed: Feed?
+    
+}

Reader/Reader.xcdatamodeld/Reader.xcdatamodel/contents

@@ -4,7 +4,7 @@
         <attribute name="id" attributeType="String"/>
         <attribute name="lastUpdated" optional="YES" attributeType="Date" usesScalarValueType="NO"/>
         <attribute name="title" attributeType="String"/>
-        <attribute name="url" attributeType="URI"/>
+        <attribute name="url" optional="YES" attributeType="URI"/>
         <relationship name="groups" toMany="YES" deletionRule="Nullify" destinationEntity="Group" inverseName="feeds" inverseEntity="Group"/>
         <relationship name="items" toMany="YES" deletionRule="Nullify" destinationEntity="Item" inverseName="feed" inverseEntity="Item"/>
     </entity>
@@ -13,19 +13,23 @@
         <attribute name="title" attributeType="String"/>
         <relationship name="feeds" toMany="YES" deletionRule="Nullify" destinationEntity="Feed" inverseName="groups" inverseEntity="Feed"/>
     </entity>
-    <entity name="Item" representedClassName="Item" syncable="YES" codeGenerationType="class">
+    <entity name="Item" representedClassName="Item" syncable="YES">
         <attribute name="author" optional="YES" attributeType="String"/>
         <attribute name="content" optional="YES" attributeType="String"/>
-        <attribute name="id" optional="YES" attributeType="String"/>
+        <attribute name="id" attributeType="String"/>
         <attribute name="published" optional="YES" attributeType="Date" usesScalarValueType="NO"/>
-        <attribute name="read" optional="YES" attributeType="Boolean" usesScalarValueType="YES"/>
+        <attribute name="read" attributeType="Boolean" usesScalarValueType="YES"/>
         <attribute name="title" optional="YES" attributeType="String"/>
         <attribute name="url" optional="YES" attributeType="URI"/>
         <relationship name="feed" maxCount="1" deletionRule="Nullify" destinationEntity="Feed" inverseName="items" inverseEntity="Feed"/>
     </entity>
+    <entity name="SyncState" representedClassName="SyncState" syncable="YES" codeGenerationType="class">
+        <attribute name="lastSync" attributeType="Date" usesScalarValueType="NO"/>
+    </entity>
     <elements>
-        <element name="Group" positionX="-63" positionY="-18" width="128" height="74"/>
         <element name="Feed" positionX="-54" positionY="9" width="128" height="119"/>
+        <element name="Group" positionX="-63" positionY="-18" width="128" height="74"/>
         <element name="Item" positionX="-45" positionY="63" width="128" height="149"/>
+        <element name="SyncState" positionX="-63" positionY="90" width="128" height="44"/>
     </elements>
 </model>

Reader/SceneDelegate.swift

@@ -70,7 +70,7 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
         window!.rootViewController = nav
             
         Task(priority: .userInitiated) {
-            await self.fervorController.syncGroupsAndFeeds()
+            await self.fervorController.syncAll()
             await self.fetchFeeds()
         }
     }

Reader/Screens/Home/HomeViewController.swift

@@ -8,7 +8,7 @@
 import UIKit
 import CoreData
 
-class HomeViewController: UIViewController, UICollectionViewDelegate {
+class HomeViewController: UIViewController {
     
     let fervorController: FervorController
     
@@ -50,8 +50,6 @@ class HomeViewController: UIViewController, UICollectionViewDelegate {
         
         dataSource = createDataSource()
         
-        // todo: maybe NSFetchedResultsController to automatically update when the database changes?
-//        applyInitialSnapshot()
         var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
         snapshot.appendSections([.groups, .feeds])
         dataSource.apply(snapshot, animatingDifferences: false)
@@ -83,17 +81,6 @@ class HomeViewController: UIViewController, UICollectionViewDelegate {
         return dataSource
     }
     
-//    private func applyInitialSnapshot() {
-//        let groups = try! fervorController.persistentContainer.viewContext.fetch(Group.fetchRequest())
-//        let feeds = try! fervorController.persistentContainer.viewContext.fetch(Feed.fetchRequest())
-//
-//        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
-//        snapshot.appendSections([.groups, .feeds])
-//        snapshot.appendItems(groups.map { .group($0) }, toSection: .groups)
-//        snapshot.appendItems(feeds.map { .feed($0) }, toSection: .feeds)
-//        dataSource.apply(snapshot, animatingDifferences: false)
-//    }
-    
 }
 
 extension HomeViewController {
@@ -134,3 +121,20 @@ extension HomeViewController: NSFetchedResultsControllerDelegate {
         dataSource.apply(snapshot, animatingDifferences: false)
     }
 }
+
+extension HomeViewController: UICollectionViewDelegate {
+    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
+        collectionView.deselectItem(at: indexPath, animated: true)
+        guard let item = dataSource.itemIdentifier(for: indexPath) else {
+            return
+        }
+        let req = Reader.Item.fetchRequest()
+        switch item {
+        case .group(let group):
+            req.predicate = NSPredicate(format: "feed in %@", group.feeds!)
+        case .feed(let feed):
+            req.predicate = NSPredicate(format: "feed = %@", feed)
+        }
+        show(ItemsViewController(fervorController: fervorController, fetchRequest: req), sender: nil)
+    }
+}

Reader/Screens/Items/ItemsViewController.swift

@@ -0,0 +1,82 @@
+//
+//  ItemsViewController.swift
+//  Reader
+//
+//  Created by Shadowfacts on 1/9/22.
+//
+
+import UIKit
+import CoreData
+
+class ItemsViewController: UIViewController {
+    
+    let fervorController: FervorController
+    let fetchRequest: NSFetchRequest<Item>
+    
+    private var collectionView: UICollectionView!
+    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
+    private var resultsController: NSFetchedResultsController<Item>!
+    
+    init(fervorController: FervorController, fetchRequest: NSFetchRequest<Item>) {
+        self.fervorController = fervorController
+        self.fetchRequest = fetchRequest
+        
+        super.init(nibName: nil, bundle: nil)
+    }
+    
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+
+    override func viewDidLoad() {
+        super.viewDidLoad()
+
+        let configuration = UICollectionLayoutListConfiguration(appearance: .plain)
+        let layout = UICollectionViewCompositionalLayout.list(using: configuration)
+        collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
+        collectionView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
+        view.addSubview(collectionView)
+        
+        dataSource = createDataSource()
+        
+        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
+        snapshot.appendSections([.items])
+        dataSource.apply(snapshot, animatingDifferences: false)
+        
+        fetchRequest.sortDescriptors = [NSSortDescriptor(key: "published", ascending: false)]
+        resultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: fervorController.persistentContainer.viewContext, sectionNameKeyPath: nil, cacheName: nil)
+        resultsController.delegate = self
+        try! resultsController.performFetch()
+    }
+    
+    private func createDataSource() -> UICollectionViewDiffableDataSource<Section, Item> {
+        let listCell = UICollectionView.CellRegistration<UICollectionViewListCell, Item> { cell, indexPath, item in
+            var config = cell.defaultContentConfiguration()
+            config.text = item.title
+            cell.contentConfiguration = config
+            
+            cell.accessories = [.disclosureIndicator()]
+        }
+        let dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: collectionView) { collectionView, indexPath, item in
+            return collectionView.dequeueConfiguredReusableCell(using: listCell, for: indexPath, item: item)
+        }
+        return dataSource
+    }
+
+}
+
+extension ItemsViewController {
+    enum Section: Hashable {
+        case items
+    }
+}
+
+extension ItemsViewController: NSFetchedResultsControllerDelegate {
+    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith snapshot: NSDiffableDataSourceSnapshotReference) {
+        var snapshot = self.dataSource.snapshot()
+        snapshot.deleteItems(snapshot.itemIdentifiers(inSection: .items))
+        // use resultsController here instead of controller so we don't have to cast
+        snapshot.appendItems(resultsController.fetchedObjects!, toSection: .items)
+        self.dataSource.apply(snapshot, animatingDifferences: false)
+    }
+}