fix: empty banner could be preview issue

Mastodon/Protocol/Provider/DataSourceFacade+Media.swift

@@ -5,6 +5,7 @@
 //  Created by MainasuK on 2022-1-26.
 //
 
+import os.log
 import UIKit
 import CoreDataStack
 import MastodonUI
@@ -153,6 +154,8 @@ extension DataSourceFacade {
         user: ManagedObjectRecord<MastodonUser>,
         previewContext: ImagePreviewContext
     ) async throws {
+        let logger = Logger(subsystem: "DataSourceFacade", category: "Media")
+        
         let managedObjectContext = dependency.context.managedObjectContext
         
         var _avatarAssetURL: String?
@@ -216,13 +219,18 @@ extension DataSourceFacade {
                     thumbnail: thumbnail
                 ))
             case .profileBanner:
-                return .profileAvatar(.init(
+                return .profileBanner(.init(
                     assetURL: _headerAssetURL,
                     thumbnail: thumbnail
                 ))
             }
         }()
         
+        guard mediaPreviewItem.isAssetURLValid else {
+            logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): discard preview due to assetURL invalid")
+            return
+        }
+        
         coordinateToMediaPreviewScene(
             dependency: dependency,
             mediaPreviewItem: mediaPreviewItem,

Mastodon/Scene/MediaPreview/MediaPreviewViewModel.swift

@@ -116,6 +116,19 @@ extension MediaPreviewViewModel {
         case profileAvatar(ProfileAvatarPreviewContext)
         case profileBanner(ProfileBannerPreviewContext)
 //        case local(LocalImagePreviewMeta)
+        
+        var isAssetURLValid: Bool {
+            switch self {
+            case .attachment:
+                return true     // default valid
+            case .profileAvatar:
+                return true     // default valid
+            case .profileBanner(let item):
+                guard let assertURL = item.assetURL else { return false }
+                guard !assertURL.hasSuffix("missing.png") else { return false }
+                return true
+            }
+        }
     }
     
     struct AttachmentPreviewContext {