Refactoring and tidy up.

Make the preview manager a singleton (passing in the MXSession to functions). Fix tests.

PreviewManager → URLPreviewManager
URLPreviewViewData → URLPreviewData
URLPreviewCache → URLPreviewStore

Riot/Managers/URLPreviews/URLPreviewStore.swift

@@ -0,0 +1,158 @@
+// 
+// Copyright 2021 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import CoreData
+
+/// A cache for URL previews backed by Core Data.
+class URLPreviewStore {
+    
+    // MARK: - Properties
+    
+    /// The Core Data container for persisting the cache to disk.
+    private let container: NSPersistentContainer
+    
+    /// The Core Data context used to store and load data on.
+    private var context: NSManagedObjectContext {
+        container.viewContext
+    }
+    
+    /// A time interval that represents how long an item in the cache is valid for.
+    private let dataValidityTime: TimeInterval = 60 * 60 * 24
+    
+    /// The oldest `creationDate` allowed for valid data.
+    private var expiryDate: Date {
+        Date().addingTimeInterval(-dataValidityTime)
+    }
+    
+    // MARK: - Lifecycle
+    
+    /// Create a URLPreview Cache optionally storing the data in memory.
+    /// - Parameter inMemory: Whether to store the data in memory.
+    init(inMemory: Bool = false) {
+        // Register the transformer for the `image` field.
+        ValueTransformer.setValueTransformer(URLPreviewImageTransformer(), forName: .urlPreviewImageTransformer)
+        
+        // Create the container, updating it's path if storing the data in memory.
+        container = NSPersistentContainer(name: "URLPreviewStore")
+        
+        if inMemory {
+            container.persistentStoreDescriptions.first?.url = URL(fileURLWithPath: "/dev/null")
+        }
+        
+        // Load the persistent stores into the container
+        container.loadPersistentStores { storeDescription, error in
+            if let error = error {
+                MXLog.error("[URLPreviewStore] Core Data container error: \(error.localizedDescription)")
+            }
+        }
+    }
+    
+    // MARK: - Public
+    
+    /// Store a preview in the cache. If a preview already exists with the same URL it will be updated from the new preview.
+    /// - Parameter preview: The preview to add to the cache.
+    /// - Parameter date: Optional: The date the preview was generated.
+    func store(_ preview: URLPreviewData, generatedOn generationDate: Date? = nil) {
+        // Create a fetch request for an existing preview.
+        let request: NSFetchRequest<URLPreviewCacheData> = URLPreviewCacheData.fetchRequest()
+        request.predicate = NSPredicate(format: "url == %@", preview.url as NSURL)
+        
+        // Use the custom date if supplied (currently this is for testing purposes)
+        let date = generationDate ?? Date()
+        
+        // Update existing data if found otherwise create new data.
+        if let cachedPreview = try? context.fetch(request).first {
+            cachedPreview.update(from: preview, on: date)
+        } else {
+            _ = URLPreviewCacheData(context: context, preview: preview, creationDate: date)
+        }
+        
+        save()
+    }
+    
+    /// Fetches the preview from the cache for the supplied URL. If a preview doesn't exist or
+    /// if the preview is older than the ``dataValidityTime`` the returned value will be nil.
+    /// - Parameter url: The URL to fetch the preview for.
+    /// - Returns: The preview if found, otherwise nil.
+    func preview(for url: URL, and event: MXEvent) -> URLPreviewData? {
+        // Create a request for the url excluding any expired items
+        let request: NSFetchRequest<URLPreviewCacheData> = URLPreviewCacheData.fetchRequest()
+        request.predicate = NSCompoundPredicate(type: .and, subpredicates: [
+            NSPredicate(format: "url == %@", url as NSURL),
+            NSPredicate(format: "creationDate > %@", expiryDate as NSDate)
+        ])
+        
+        // Fetch the request, returning nil if nothing was found
+        guard
+            let cachedPreview = try? context.fetch(request).first
+        else { return nil }
+        
+        // Convert and return
+        return cachedPreview.preview(for: event)
+    }
+    
+    /// Returns the number of URL previews cached in the store.
+    func cacheCount() -> Int {
+        let request: NSFetchRequest<NSFetchRequestResult> = URLPreviewCacheData.fetchRequest()
+        return (try? context.count(for: request)) ?? 0
+    }
+    
+    /// Removes any expired cache data from the store.
+    func removeExpiredItems() {
+        let request: NSFetchRequest<NSFetchRequestResult> = URLPreviewCacheData.fetchRequest()
+        request.predicate = NSPredicate(format: "creationDate < %@", expiryDate as NSDate)
+        
+        do {
+            try context.execute(NSBatchDeleteRequest(fetchRequest: request))
+        } catch {
+            MXLog.error("[URLPreviewStore] Error executing batch delete request: \(error.localizedDescription)")
+        }
+    }
+    
+    /// Deletes all cache data and all closed previews from the store.
+    func deleteAll() {
+        do {
+            _ = try context.execute(NSBatchDeleteRequest(fetchRequest: URLPreviewCacheData.fetchRequest()))
+            _ = try context.execute(NSBatchDeleteRequest(fetchRequest: ClosedURLPreview.fetchRequest()))
+        } catch {
+            MXLog.error("[URLPreviewStore] Error executing batch delete request: \(error.localizedDescription)")
+        }
+    }
+    
+    func closePreview(for eventID: String, in roomID: String) {
+        _ = ClosedURLPreview(context: context, eventID: eventID, roomID: roomID)
+        save()
+    }
+    
+    func hasClosedPreview(for eventID: String, in roomID: String) -> Bool {
+        // Create a request for the url excluding any expired items
+        let request: NSFetchRequest<ClosedURLPreview> = ClosedURLPreview.fetchRequest()
+        request.predicate = NSCompoundPredicate(type: .and, subpredicates: [
+            NSPredicate(format: "eventID == %@", eventID),
+            NSPredicate(format: "roomID == %@", roomID)
+        ])
+        
+        return (try? context.count(for: request)) ?? 0 > 0
+    }
+    
+    // MARK: - Private
+    
+    /// Saves any changes that are found on the context
+    private func save() {
+        guard context.hasChanges else { return }
+        try? context.save()
+    }
+}