From bcf2a2f0266c3363256f921d09f24478615384fa Mon Sep 17 00:00:00 2001
From: Shadowfacts <me@shadowfacts.net>
Date: Mon, 22 Jul 2024 22:48:00 -0700
Subject: [PATCH] Improve compose reply view avatar scrolling animation

---
 .../ComposeUI/TextViewCaretScrolling.swift    |  1 +
 .../ComposeUI/Views/ReplyStatusView.swift     | 52 ++++++++++++++++---
 2 files changed, 46 insertions(+), 7 deletions(-)

diff --git a/Packages/ComposeUI/Sources/ComposeUI/TextViewCaretScrolling.swift b/Packages/ComposeUI/Sources/ComposeUI/TextViewCaretScrolling.swift
index aa38ce18..a1f81f7d 100644
--- a/Packages/ComposeUI/Sources/ComposeUI/TextViewCaretScrolling.swift
+++ b/Packages/ComposeUI/Sources/ComposeUI/TextViewCaretScrolling.swift
@@ -39,6 +39,7 @@ extension TextViewCaretScrolling {
         
         let animator = UIViewPropertyAnimator(duration: 0.2, curve: .easeInOut) {
             scrollView.scrollRectToVisible(rectToMakeVisible, animated: false)
+            scrollView.layoutIfNeeded()
         }
         self.caretScrollPositionAnimator = animator
         animator.startAnimation()
diff --git a/Packages/ComposeUI/Sources/ComposeUI/Views/ReplyStatusView.swift b/Packages/ComposeUI/Sources/ComposeUI/Views/ReplyStatusView.swift
index 91706952..c6198897 100644
--- a/Packages/ComposeUI/Sources/ComposeUI/Views/ReplyStatusView.swift
+++ b/Packages/ComposeUI/Sources/ComposeUI/Views/ReplyStatusView.swift
@@ -76,13 +76,15 @@ struct ReplyStatusView: View {
         // once you scroll past the in-reply-to-content, the bottom of the avatar should be pinned to the bottom of the content
         offset = min(offset, maxOffset)
 
-        return AvatarImageView(
-            url: status.account.avatar,
-            size: 50,
-            style: controller.config.avatarStyle,
-            fetchAvatar: controller.fetchAvatar
-        )
-        .offset(x: 0, y: offset)
+        return AvatarContainerRepresentable(offset: offset) {
+            AvatarImageView(
+                url: status.account.avatar,
+                size: 50,
+                style: controller.config.avatarStyle,
+                fetchAvatar: controller.fetchAvatar
+            )
+        }
+        .frame(width: 50, height: 50)
         .accessibilityHidden(true)
     }
 
@@ -94,3 +96,39 @@ private struct DisplayNameHeightPrefKey: PreferenceKey {
         value = nextValue()
     }
 }
+
+// This whole dance is necessary so that the offset can be animatable from
+// UIKit animations, like TextViewCaretScrolling.
+private struct AvatarContainerRepresentable<Content: View>: UIViewControllerRepresentable {
+    let offset: CGFloat
+    @ViewBuilder let content: Content
+
+    func makeUIViewController(context: Context) -> Controller {
+        Controller(host: UIHostingController(rootView: content))
+    }
+    
+    func updateUIViewController(_ uiViewController: Controller, context: Context) {
+        uiViewController.host.rootView = content
+        uiViewController.host.view.transform = CGAffineTransform(translationX: 0, y: offset)
+    }
+ 
+    // This extra layer is necessary because applying a transform to the
+    // representable's VC's view doesn't seem to have an effect.
+    class Controller: UIViewController {
+        let host: UIHostingController<Content>
+        
+        init(host: UIHostingController<Content>) {
+            self.host = host
+            super.init(nibName: nil, bundle: nil)
+            addChild(host)
+            host.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
+            view.addSubview(host.view)
+            host.view.frame = view.bounds
+            host.didMove(toParent: self)
+        }
+        
+        required init?(coder: NSCoder) {
+            fatalError("init(coder:) has not been implemented")
+        }
+    }
+}