Update for PR feedback.

URLPreviewManager becomes URLPreviewService.
addVerticalWhitespaceToString used instead of heightForCellData multiple times.
All newline characters removed.

Riot/Managers/URLPreviews/URLPreviewService.swift

@@ -0,0 +1,159 @@
+//
+// 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 Foundation
+
+enum URLPreviewServiceError: Error {
+    case missingResponse
+}
+
+@objcMembers
+/// A service for URL preview data that handles fetching, caching and clean-up
+/// as well as remembering which previews have been closed by the user.
+class URLPreviewService: NSObject {
+    
+    // MARK: - Properties
+    
+    /// The shared service object.
+    static let shared = URLPreviewService()
+    
+    /// A persistent store backed by Core Data to reduce network requests
+    private let store = URLPreviewStore()
+    
+    // MARK: - Public
+    
+    /// Generates preview data for a URL to be previewed as part of the supplied event,
+    /// first checking the cache, and if necessary making a request to the homeserver.
+    /// You should call `hasClosedPreview` first to ensure that a preview is required.
+    /// - Parameters:
+    ///   - url: The URL to generate the preview for.
+    ///   - event: The event that the preview is for.
+    ///   - session: The session to use to contact the homeserver.
+    ///   - success: The closure called when the operation complete. The generated preview data is passed in.
+    ///   - failure: The closure called when something goes wrong. The error that occured is passed in.
+    func preview(for url: URL,
+                 and event: MXEvent,
+                 with session: MXSession,
+                 success: @escaping (URLPreviewData) -> Void,
+                 failure: @escaping (Error?) -> Void) {
+        // Sanitize the URL before checking the store or performing lookup
+        let sanitizedURL = sanitize(url)
+        
+        // Check for a valid preview in the store, and use this if found
+        if let preview = store.preview(for: sanitizedURL, and: event) {
+            MXLog.debug("[URLPreviewService] Using cached preview.")
+            success(preview)
+            return
+        }
+        
+        // Otherwise make a request to the homeserver to generate a preview
+        session.matrixRestClient.preview(for: sanitizedURL, success: { previewResponse in
+            MXLog.debug("[URLPreviewService] Cached preview not found. Requesting from homeserver.")
+            
+            guard let previewResponse = previewResponse else {
+                failure(URLPreviewServiceError.missingResponse)
+                return
+            }
+            
+            // Convert the response to preview data, fetching the image if provided.
+            self.makePreviewData(from: previewResponse, for: sanitizedURL, and: event, with: session) { previewData in
+                self.store.cache(previewData)
+                success(previewData)
+            }
+            
+        }, failure: failure)
+    }
+    
+    /// Removes any cached preview data that has expired.
+    func removeExpiredCacheData() {
+        store.removeExpiredItems()
+    }
+    
+    /// Deletes all cached preview data and closed previews from the store.
+    func clearStore() {
+        store.deleteAll()
+    }
+    
+    /// Store the `eventId` and `roomId` of a closed preview.
+    func closePreview(for eventId: String, in roomId: String) {
+        store.closePreview(for: eventId, in: roomId)
+    }
+    
+    /// Whether a preview for the given event has been closed or not.
+    func hasClosedPreview(from event: MXEvent) -> Bool {
+        store.hasClosedPreview(for: event.eventId, in: event.roomId)
+    }
+    
+    // MARK: - Private
+    
+    /// Convert an `MXURLPreview` object into `URLPreviewData` whilst also getting the image via the media manager.
+    /// - Parameters:
+    ///   - previewResponse: The `MXURLPreview` object to convert.
+    ///   - url: The URL that response was for.
+    ///   - event: The event that the URL preview is for.
+    ///   - session: The session to use to for media management.
+    ///   - completion: A closure called when the operation completes. This contains the preview data.
+    private func makePreviewData(from previewResponse: MXURLPreview,
+                         for url: URL,
+                         and event: MXEvent,
+                         with session: MXSession,
+                         completion: @escaping (URLPreviewData) -> Void) {
+        // Create the preview data and return if no image is needed.
+        let previewData = URLPreviewData(url: url,
+                                         eventID: event.eventId,
+                                         roomID: event.roomId,
+                                         siteName: previewResponse.siteName,
+                                         title: previewResponse.title,
+                                         text: previewResponse.text)
+        
+        guard let imageURL = previewResponse.imageURL else {
+            completion(previewData)
+            return
+        }
+        
+        // Check for an image in the media cache and use this if found.
+        if let cachePath = MXMediaManager.cachePath(forMatrixContentURI: imageURL, andType: previewResponse.imageType, inFolder: nil),
+           let image = MXMediaManager.loadThroughCache(withFilePath: cachePath) {
+            previewData.image = image
+            completion(previewData)
+            return
+        }
+        
+        // Don't de-dupe image downloads as the service should de-dupe preview generation.
+        
+        // Otherwise download the image from the homeserver, treating an error as a preview without an image.
+        session.mediaManager.downloadMedia(fromMatrixContentURI: imageURL, withType: previewResponse.imageType, inFolder: nil) { path in
+            guard let image = MXMediaManager.loadThroughCache(withFilePath: path) else {
+                completion(previewData)
+                return
+            }
+            previewData.image = image
+            completion(previewData)
+        } failure: { error in
+            completion(previewData)
+        }
+    }
+    
+    /// Returns a URL created from the URL passed in, with sanitizations applied to reduce
+    /// queries and duplicate cache data for URLs that will return the same preview data.
+    private func sanitize(_ url: URL) -> URL {
+        // Remove the fragment from the URL.
+        var components = URLComponents(url: url, resolvingAgainstBaseURL: false)
+        components?.fragment = nil
+        
+        return components?.url ?? url
+    }
+}