Add image prefetch to the timeline + resize close #931 (#930)

* Add image prefectch to the timeline

* Use preview url for post with multiple attachements

* Add image resize

* Prefetch link cards

---------

Co-authored-by: Thomas Ricouard <ricouard77@gmail.com>

Packages/Status/Sources/Status/Row/Subviews/StatusRowMediaPreviewView.swift

@@ -166,6 +166,7 @@ public struct StatusRowMediaPreviewView: View {
               .frame(width: newSize.width, height: newSize.height)
           }
         }
+        .processors([ImageProcessors.Resize(size: .init(width: newSize.width, height: newSize.height))])
         .frame(width: newSize.width, height: newSize.height)
 
       case .gifv, .video, .audio:
@@ -205,13 +206,14 @@ public struct StatusRowMediaPreviewView: View {
         GeometryReader { proxy in
           switch type {
           case .image:
+            let width = isNotifications ? imageMaxHeight : proxy.frame(in: .local).width
             ZStack(alignment: .bottomTrailing) {
-              LazyImage(url: attachment.url) { state in
+              LazyImage(url: attachment.previewUrl ?? attachment.url) { state in
                 if let image = state.imageContainer?.image {
                   SwiftUI.Image(uiImage: image)
                     .resizable()
                     .aspectRatio(contentMode: .fill)
-                    .frame(maxWidth: isNotifications ? imageMaxHeight : proxy.frame(in: .local).width)
+                    .frame(maxWidth: width)
                     .frame(maxHeight: imageMaxHeight)
                     .clipped()
                     .cornerRadius(4)
@@ -219,9 +221,10 @@ public struct StatusRowMediaPreviewView: View {
                   RoundedRectangle(cornerRadius: 4)
                     .fill(Color.gray)
                     .frame(maxHeight: imageMaxHeight)
-                    .frame(maxWidth: isNotifications ? imageMaxHeight : proxy.frame(in: .local).width)
+                    .frame(maxWidth: width)
                 }
               }
+              .processors([ImageProcessors.Resize(size: .init(width: width, height: imageMaxHeight))])
               if sensitive {
                 cornerSensitiveButton
               }

Packages/Timeline/Sources/Timeline/TimelinePrefetcher.swift

@@ -0,0 +1,42 @@
+import SwiftUI
+import UIKit
+import Models
+import Nuke
+
+final class TimelinePrefetcher: NSObject, ObservableObject, UICollectionViewDataSourcePrefetching {
+  private let prefetcher = ImagePrefetcher()
+
+  weak var viewModel: TimelineViewModel?
+
+  func collectionView(_ collectionView: UICollectionView, prefetchItemsAt indexPaths: [IndexPath]) {
+    let imageURLs = getImageURLs(for: indexPaths)
+    prefetcher.startPrefetching(with: imageURLs)
+  }
+
+    func collectionView(_ collectionView: UICollectionView, cancelPrefetchingForItemsAt indexPaths: [IndexPath]) {
+    let imageURLs = getImageURLs(for: indexPaths)
+    prefetcher.stopPrefetching(with: imageURLs)
+  }
+
+  private func getImageURLs(for indexPaths: [IndexPath]) -> [URL] {
+    guard let viewModel, case .display(let statuses, _) = viewModel.statusesState else {
+      return []
+    }
+    return indexPaths.compactMap {
+      $0.row < statuses.endIndex ? statuses[$0.row] : nil
+    }.flatMap(getImages)
+  }
+}
+
+private func getImages(for status: Status) -> [URL] {
+  var urls = status.mediaAttachments.compactMap {
+    if $0.supportedType == .image {
+      return status.mediaAttachments.count > 1 ? $0.previewUrl ?? $0.url : $0.url
+    }
+    return nil
+  }
+  if let url = status.card?.image {
+    urls.append(url)
+  }
+  return urls
+}

Packages/Timeline/Sources/Timeline/TimelineView.swift

@@ -20,6 +20,7 @@ public struct TimelineView: View {
   @EnvironmentObject private var routerPath: RouterPath
 
   @StateObject private var viewModel = TimelineViewModel()
+  @StateObject private var prefetcher = TimelinePrefetcher()
 
   @State private var wasBackgrounded: Bool = false
   @State private var collectionView: UICollectionView?
@@ -53,10 +54,12 @@ public struct TimelineView: View {
         .listStyle(.plain)
         .scrollContentBackground(.hidden)
         .background(theme.primaryBackgroundColor)
-        .introspect(selector: TargetViewSelector.ancestorOrSiblingContaining,
-                    customize: { (collectionView: UICollectionView) in
-                      self.collectionView = collectionView
-                    })
+        .introspect(selector: TargetViewSelector.ancestorOrSiblingContaining) { (collectionView: UICollectionView) in
+          self.collectionView = collectionView
+          self.prefetcher.viewModel = viewModel
+          collectionView.isPrefetchingEnabled = true
+          collectionView.prefetchDataSource = self.prefetcher
+        }
         if viewModel.pendingStatusesEnabled {
           PendingStatusesObserverView(observer: viewModel.pendingStatusesObserver)
         }