Prefetch media

Caches/PrefetchRequestModifier.swift

@@ -0,0 +1,15 @@
+// Copyright © 2021 Metabolist. All rights reserved.
+
+import Foundation
+import Kingfisher
+
+struct PrefetchRequestModifier: ImageDownloadRequestModifier {
+    func modified(for request: URLRequest) -> URLRequest? {
+        var mutableRequest = request
+
+        mutableRequest.allowsExpensiveNetworkAccess = false
+        mutableRequest.allowsConstrainedNetworkAccess = false
+
+        return request
+    }
+}

Extensions/CollectionItem+Extensions.swift

@@ -1,5 +1,6 @@
 // Copyright © 2020 Metabolist. All rights reserved.
 
+import Mastodon
 import UIKit
 import ViewModels
 
@@ -61,4 +62,50 @@ extension CollectionItem {
             return UITableView.automaticDimension
         }
     }
+
+    func mediaPrefetchURLs(identityContext: IdentityContext) -> Set<URL> {
+        switch self {
+        case let .status(status, _):
+            return status.mediaPrefetchURLs(identityContext: identityContext)
+        case let .account(account, _):
+            return account.mediaPrefetchURLs(identityContext: identityContext)
+        case let .notification(notification, _):
+            var urls = notification.account.mediaPrefetchURLs(identityContext: identityContext)
+
+            if let status = notification.status {
+                urls.formUnion(status.mediaPrefetchURLs(identityContext: identityContext))
+            }
+
+            return urls
+        case let .conversation(conversation):
+            return conversation.accounts.reduce(Set<URL>()) {
+                $0.union($1.mediaPrefetchURLs(identityContext: identityContext))
+            }
+        default:
+            return []
+        }
+    }
+}
+
+private extension Account {
+    func mediaPrefetchURLs(identityContext: IdentityContext) -> Set<URL> {
+        var urls = Set(emojis.map(\.url))
+
+        if !identityContext.appPreferences.shouldReduceMotion
+            && identityContext.appPreferences.animateAvatars == .everywhere {
+            urls.insert(avatar)
+        } else {
+            urls.insert(avatarStatic)
+        }
+
+        return urls
+    }
+}
+
+private extension Status {
+    func mediaPrefetchURLs(identityContext: IdentityContext) -> Set<URL> {
+        displayStatus.account.mediaPrefetchURLs(identityContext: identityContext)
+            .union(displayStatus.mediaAttachments.compactMap(\.previewUrl))
+            .union(displayStatus.emojis.map(\.url))
+    }
 }

Metatext.xcodeproj/project.pbxproj

@@ -56,6 +56,7 @@
 		D036EBB8259FE29800EC1CFC /* Status+Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0849C7E25903C4900A5EBCC /* Status+Extensions.swift */; };
 		D036EBC2259FE2AD00EC1CFC /* UIVIewController+Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0E7AD3825870B13005F5E2D /* UIVIewController+Extensions.swift */; };
 		D03D87F425C23C44004DCBB2 /* SecondaryNavigationTitleView.swift in Sources */ = {isa = PBXBuildFile; fileRef = D03D87F325C23C44004DCBB2 /* SecondaryNavigationTitleView.swift */; };
+		D0477F1525C68BAC005C5368 /* PrefetchRequestModifier.swift in Sources */ = {isa = PBXBuildFile; fileRef = D0477F1425C68BAC005C5368 /* PrefetchRequestModifier.swift */; };
 		D04F9E8E259E9C950081B0C9 /* ViewModels in Frameworks */ = {isa = PBXBuildFile; productRef = D04F9E8D259E9C950081B0C9 /* ViewModels */; };
 		D05936CF25A8D79800754FDF /* EditAttachmentViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D05936CE25A8D79800754FDF /* EditAttachmentViewController.swift */; };
 		D05936D025A8D79800754FDF /* EditAttachmentViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D05936CE25A8D79800754FDF /* EditAttachmentViewController.swift */; };
@@ -251,6 +252,7 @@
 		D036AA0B254B612B009094DF /* NotificationContentConfiguration.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NotificationContentConfiguration.swift; sourceTree = "<group>"; };
 		D036AA16254CA823009094DF /* StatusBodyView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StatusBodyView.swift; sourceTree = "<group>"; };
 		D03D87F325C23C44004DCBB2 /* SecondaryNavigationTitleView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SecondaryNavigationTitleView.swift; sourceTree = "<group>"; };
+		D0477F1425C68BAC005C5368 /* PrefetchRequestModifier.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PrefetchRequestModifier.swift; sourceTree = "<group>"; };
 		D047FA8C24C3E21200AF17C5 /* Metatext.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = Metatext.app; sourceTree = BUILT_PRODUCTS_DIR; };
 		D05936CE25A8D79800754FDF /* EditAttachmentViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = EditAttachmentViewController.swift; sourceTree = "<group>"; };
 		D05936DD25A937EC00754FDF /* EditThumbnailView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = EditThumbnailView.swift; sourceTree = "<group>"; };
@@ -737,6 +739,7 @@
 				D025B14C25C4E482001C69A8 /* ImageCacheConfiguration.swift */,
 				D025B14525C4D26A001C69A8 /* ImageCacheSerializer.swift */,
 				D0FE1C9725368A9D003EF1EB /* PlayerCache.swift */,
+				D0477F1425C68BAC005C5368 /* PrefetchRequestModifier.swift */,
 			);
 			path = Caches;
 			sourceTree = "<group>";
@@ -967,6 +970,7 @@
 				D08B8D622540DE3B00B1EBEF /* ZoomTransitionController.swift in Sources */,
 				D0F0B12E251A97E400942152 /* TableViewController.swift in Sources */,
 				D0DD50CB256B1F24004A04F7 /* ReportView.swift in Sources */,
+				D0477F1525C68BAC005C5368 /* PrefetchRequestModifier.swift in Sources */,
 				D097F41B25BE3E1A00859F2C /* SearchScope+Extensions.swift in Sources */,
 				D035F8B325B9616000DC75ED /* Timeline+Extensions.swift in Sources */,
 				D0FE1C8F253686F9003EF1EB /* PlayerView.swift in Sources */,

View Controllers/TableViewController.swift

@@ -2,6 +2,7 @@
 
 import AVKit
 import Combine
+import Kingfisher
 import Mastodon
 import SafariServices
 import SwiftUI
@@ -48,6 +49,7 @@ class TableViewController: UITableViewController {
         super.viewDidLoad()
 
         tableView.dataSource = dataSource
+        tableView.prefetchDataSource = self
         tableView.cellLayoutMarginsFollowReadableWidth = true
         tableView.tableFooterView = UIView()
         tableView.contentInset.bottom = bottomInset
@@ -189,6 +191,20 @@ extension TableViewController {
     }
 }
 
+extension TableViewController: UITableViewDataSourcePrefetching {
+    func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
+        let urls = indexPaths.compactMap(dataSource.itemIdentifier(for:))
+            .reduce(Set<URL>()) { $0.union($1.mediaPrefetchURLs(identityContext: viewModel.identityContext)) }
+        var imageOptions = KingfisherManager.shared.defaultOptions
+
+        imageOptions.append(.requestModifier(PrefetchRequestModifier()))
+
+        for url in urls {
+            KingfisherManager.shared.retrieveImage(with: url, completionHandler: nil)
+        }
+    }
+}
+
 extension TableViewController: AVPlayerViewControllerDelegate {
     func playerViewController(
         _ playerViewController: AVPlayerViewController,