Use thumbnails in media views.

Signal/src/ViewControllers/MediaGalleryViewController.swift

@@ -8,17 +8,28 @@ public enum GalleryDirection {
     case before, after, around
 }
 
-public struct MediaGalleryItem: Equatable, Hashable {
+public class MediaGalleryItem: Equatable, Hashable {
     let logTag = "[MediaGalleryItem]"
 
     let message: TSMessage
     let attachmentStream: TSAttachmentStream
     let galleryDate: GalleryDate
 
+    var presentationImage: UIImage?
+
     init(message: TSMessage, attachmentStream: TSAttachmentStream) {
         self.message = message
         self.attachmentStream = attachmentStream
         self.galleryDate = GalleryDate(message: message)
+
+        self.presentationImage = attachmentStream.thumbnailImageLarge(success: { [weak self] (image) in
+            guard let strongSelf = self else {
+                return
+            }
+            strongSelf.presentationImage = image
+        }, failure: {
+            Logger.warn("Could not load presentation image.")
+        })
     }
 
     var isVideo: Bool {
@@ -38,15 +49,6 @@ public struct MediaGalleryItem: Equatable, Hashable {
         return attachmentStream.thumbnailImageSmall(success: async, failure: {})
     }
 
-    var fullSizedImage: UIImage {
-        guard let image = attachmentStream.originalImage else {
-            owsFail("\(logTag) in \(#function) unexpectedly unable to build attachment image")
-            return UIImage()
-        }
-
-        return image
-    }
-
     // MARK: Equatable
 
     public static func == (lhs: MediaGalleryItem, rhs: MediaGalleryItem) -> Bool {
@@ -304,7 +306,7 @@ class MediaGalleryViewController: OWSNavigationController, MediaGalleryDataSourc
 
         // loadView hasn't necessarily been called yet.
         self.loadViewIfNeeded()
-        self.presentationView.image = initialDetailItem.fullSizedImage
+        self.presentationView.image = initialDetailItem.presentationImage
         self.applyInitialMediaViewConstraints()
 
         // Restore presentationView.alpha in case a previous dismiss left us in a bad state.
@@ -481,7 +483,7 @@ class MediaGalleryViewController: OWSNavigationController, MediaGalleryDataSourc
         // it sits on the screen in the conversation view.
         let changedItems = currentItem != self.initialDetailItem
         if changedItems {
-            self.presentationView.image = currentItem.fullSizedImage
+            self.presentationView.image = currentItem.presentationImage
             self.applyOffscreenMediaViewConstraints()
         } else {
             self.applyInitialMediaViewConstraints()