Hide the ALT button when alt text is unavailable

Mastodon/Scene/MediaPreview/AltViewController.swift

@@ -8,12 +8,12 @@
 import SwiftUI
 
 class AltViewController: UIViewController {
-    var alt: String?
+    private var alt: String
     let label = UILabel()
 
-    convenience init(alt: String?, sourceView: UIView?) {
-        self.init(nibName: nil, bundle: nil)
+    init(alt: String, sourceView: UIView?) {
         self.alt = alt
+        super.init(nibName: nil, bundle: nil)
         self.modalPresentationStyle = .popover
         self.popoverPresentationController?.delegate = self
         self.popoverPresentationController?.permittedArrowDirections = .up
@@ -21,10 +21,6 @@ class AltViewController: UIViewController {
         self.overrideUserInterfaceStyle = .dark
     }
 
-    @objc override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
-        super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
-    }
-
     @MainActor required dynamic init?(coder aDecoder: NSCoder) {
         fatalError("init(coder:) has not been implemented")
     }
@@ -37,7 +33,7 @@ class AltViewController: UIViewController {
         label.lineBreakMode = .byWordWrapping
         label.lineBreakStrategy = .standard
         label.font = .preferredFont(forTextStyle: .callout)
-        label.text = alt ?? "ummmmmmm tbd but you shouldn’t see this"
+        label.text = alt
 
         view.translatesAutoresizingMaskIntoConstraints = false
         view.addSubview(label)

Mastodon/Scene/MediaPreview/Image/MediaPreviewImageViewController.swift

@@ -110,10 +110,6 @@ extension MediaPreviewImageViewController: MediaPreviewPage {
             }
         }
     }
-
-    var altText: String? {
-        viewModel.item.altText
-    }
 }
 
 // MARK: - ImageAnalysisInteractionDelegate

Mastodon/Scene/MediaPreview/MediaPreviewViewController.swift

@@ -141,6 +141,20 @@ extension MediaPreviewViewController {
             }
             .store(in: &disposeBag)
 
+        viewModel.$altText
+            .receive(on: DispatchQueue.main)
+            .sink { [weak self] altText in
+                guard let self else { return }
+                UIView.animate(withDuration: 0.3) {
+                    if altText == nil {
+                        self.altButton.alpha = 0
+                    } else {
+                        self.altButton.alpha = 1
+                    }
+                }
+            }
+            .store(in: &disposeBag)
+
         viewModel.$showingChrome
             .receive(on: DispatchQueue.main)
             .removeDuplicates()
@@ -184,7 +198,8 @@ extension MediaPreviewViewController {
 
     @objc private func altButtonPressed(_ sender: UIButton) {
         os_log(.info, log: .debug, "%{public}s[%{public}ld], %{public}s", ((#file as NSString).lastPathComponent), #line, #function)
-        present(AltViewController(alt: viewModel.viewControllers[viewModel.currentPage].altText, sourceView: sender), animated: true)
+        guard let alt = viewModel.altText else { return }
+        present(AltViewController(alt: alt, sourceView: sender), animated: true)
     }
 
 }

Mastodon/Scene/MediaPreview/MediaPreviewViewModel.swift

@@ -14,7 +14,6 @@ import MastodonCore
 
 protocol MediaPreviewPage: UIViewController {
     func setShowingChrome(_ showingChrome: Bool)
-    var altText: String? { get }
 }
 
 final class MediaPreviewViewModel: NSObject {
@@ -28,6 +27,7 @@ final class MediaPreviewViewModel: NSObject {
     
     @Published var currentPage: Int
     @Published var showingChrome = true
+    @Published var altText: String?
 
     // output
     let viewControllers: [MediaPreviewPage]
@@ -43,8 +43,11 @@ final class MediaPreviewViewModel: NSObject {
         self.item = item
         var currentPage = 0
         var viewControllers: [MediaPreviewPage] = []
+        var getAltText = { (page: Int) -> String? in nil }
         switch item {
         case .attachment(let previewContext):
+            getAltText = { previewContext.attachments[$0].altDescription }
+
             currentPage = previewContext.initialIndex
             for (i, attachment) in previewContext.attachments.enumerated() {
                 switch attachment.kind {
@@ -117,6 +120,10 @@ final class MediaPreviewViewModel: NSObject {
         self.transitionItem = transitionItem
         super.init()
 
+        self.$currentPage
+            .map(getAltText)
+            .assign(to: &$altText)
+
         for viewController in viewControllers {
             self.$showingChrome
                 .sink { [weak viewController] showingChrome in

Mastodon/Scene/MediaPreview/Video/MediaPreviewVideoViewController.swift

@@ -111,10 +111,6 @@ extension MediaPreviewVideoViewController: MediaPreviewPage {
     func setShowingChrome(_ showingChrome: Bool) {
         // TODO: does this do anything?
     }
-
-    var altText: String? {
-        viewModel.item.altText
-    }
 }
 
 // MARK: - AVPlayerViewControllerDelegate

Mastodon/Scene/MediaPreview/Video/MediaPreviewVideoViewModel.swift

@@ -125,13 +125,6 @@ extension MediaPreviewVideoViewModel {
             case .gif(let mediaContext):        return mediaContext.assetURL
             }
         }
-
-        var altText: String? {
-            switch self {
-            case .video(let mediaContext):      return mediaContext.altText
-            case .gif(let mediaContext):        return mediaContext.altText
-            }
-        }
     }
     
     struct RemoteVideoContext {