feat(swift-ios): reveal message timestamps on swipe

apps/swift-ios/Features/Chat/ThreadDetailView.swift

@@ -657,7 +657,6 @@ private struct FeatureTranscriptCollectionView: UIViewRepresentable {
         )
         collectionView.backgroundColor = T3Colors.uiBackground
         collectionView.alwaysBounceVertical = true
-        collectionView.keyboardDismissMode = .onDrag
         collectionView.delaysContentTouches = false
         collectionView.contentInsetAdjustmentBehavior = .never
         collectionView.isPrefetchingEnabled = true
@@ -710,7 +709,9 @@ private struct FeatureTranscriptCollectionView: UIViewRepresentable {
     }
 
     @MainActor
-    final class Coordinator: NSObject, UICollectionViewDataSourcePrefetching, UICollectionViewDelegate {
+    final class Coordinator: NSObject, UICollectionViewDataSourcePrefetching,
+        UICollectionViewDelegate, UIGestureRecognizerDelegate
+    {
         private struct MarkdownPrefetch {
             let revision: MarkdownContentRevision
             let task: Task<Void, Never>
@@ -731,12 +732,22 @@ private struct FeatureTranscriptCollectionView: UIViewRepresentable {
         private var markdownPrefetches: [String: MarkdownPrefetch] = [:]
         private var onLoadEarlier: (() -> Void)?
         private var onDismissKeyboard: (() -> Void)?
+        private let timestampReveal = FeatureTimestampRevealState()
+        private var verticalDragStartOffset: CGFloat?
+        private lazy var timestampPanGesture = UIPanGestureRecognizer(
+            target: self,
+            action: #selector(handleTimestampPan(_:))
+        )
 
         deinit {
             markdownPrefetches.values.forEach { $0.task.cancel() }
         }
 
         func connect(to collectionView: UICollectionView) {
+            timestampPanGesture.cancelsTouchesInView = false
+            timestampPanGesture.delegate = self
+            collectionView.addGestureRecognizer(timestampPanGesture)
+
             let registration = UICollectionView.CellRegistration<UICollectionViewCell, String> {
                 [weak self] cell, _, messageID in
                 if messageID == FeatureTranscriptCollectionView.loadEarlierID {
@@ -770,7 +781,10 @@ private struct FeatureTranscriptCollectionView: UIViewRepresentable {
                 }
 
                 cell.contentConfiguration = UIHostingConfiguration {
-                    FeatureMessageView(message: message)
+                    FeatureTimestampRevealMessageView(
+                        message: message,
+                        reveal: self?.timestampReveal ?? FeatureTimestampRevealState()
+                    )
                         .frame(maxWidth: .infinity, alignment: .leading)
                 }
                 .margins(.all, 0)
@@ -791,6 +805,71 @@ private struct FeatureTranscriptCollectionView: UIViewRepresentable {
             collectionView.delegate = self
         }
 
+        @objc private func handleTimestampPan(_ gesture: UIPanGestureRecognizer) {
+            switch gesture.state {
+            case .changed:
+                timestampReveal.width = TranscriptTimestampRevealGeometry.width(
+                    translationX: gesture.translation(in: gesture.view).x
+                )
+            case .ended, .cancelled, .failed:
+                guard timestampReveal.width > 0 else { return }
+                let duration = UIAccessibility.isReduceMotionEnabled ? 0 : 0.22
+                withAnimation(.easeOut(duration: duration)) {
+                    timestampReveal.width = 0
+                }
+            default:
+                break
+            }
+        }
+
+        func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
+            guard gestureRecognizer === timestampPanGesture,
+                  let collectionView = gestureRecognizer.view as? UICollectionView,
+                  let pan = gestureRecognizer as? UIPanGestureRecognizer else {
+                return true
+            }
+            let velocity = pan.velocity(in: collectionView)
+            guard collectionView.effectiveUserInterfaceLayoutDirection == .leftToRight else {
+                return false
+            }
+            return TranscriptTimestampRevealGeometry.shouldBegin(
+                velocityX: velocity.x,
+                velocityY: velocity.y
+            ) && !isNestedHorizontalScroller(
+                at: pan.location(in: collectionView),
+                in: collectionView
+            )
+        }
+
+        func gestureRecognizer(
+            _ gestureRecognizer: UIGestureRecognizer,
+            shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer
+        ) -> Bool {
+            guard let collectionView = timestampPanGesture.view as? UICollectionView else {
+                return false
+            }
+            return (gestureRecognizer === timestampPanGesture
+                    && otherGestureRecognizer === collectionView.panGestureRecognizer)
+                || (otherGestureRecognizer === timestampPanGesture
+                    && gestureRecognizer === collectionView.panGestureRecognizer)
+        }
+
+        private func isNestedHorizontalScroller(
+            at point: CGPoint,
+            in collectionView: UICollectionView
+        ) -> Bool {
+            var candidate = collectionView.hitTest(point, with: nil)
+            while let view = candidate, view !== collectionView {
+                if let scrollView = view as? UIScrollView,
+                   scrollView.alwaysBounceHorizontal
+                    || scrollView.contentSize.width > scrollView.bounds.width + 1 {
+                    return true
+                }
+                candidate = view.superview
+            }
+            return false
+        }
+
         func update(
             threadID: String,
             messages: [FeatureMessage],
@@ -1154,12 +1233,22 @@ private struct FeatureTranscriptCollectionView: UIViewRepresentable {
         }
 
         func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
+            verticalDragStartOffset = scrollView.contentOffset.y
+        }
+
+        func scrollViewDidScroll(_ scrollView: UIScrollView) {
+            guard let startOffset = verticalDragStartOffset,
+                  abs(scrollView.contentOffset.y - startOffset) > 0.5 else {
+                return
+            }
+            verticalDragStartOffset = nil
             (scrollView as? BottomAnchoredTranscriptCollectionView)?.maintainsBottomAnchor = false
             scrollView.window?.endEditing(false)
             onDismissKeyboard?()
         }
 
         func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
+            verticalDragStartOffset = nil
             guard !decelerate else { return }
             updateBottomAnchor(for: scrollView)
         }
@@ -1177,6 +1266,58 @@ private struct FeatureTranscriptCollectionView: UIViewRepresentable {
     }
 }
 
+enum TranscriptTimestampRevealGeometry {
+    static let maximumWidth: CGFloat = 76
+    static let minimumHorizontalVelocity: CGFloat = 120
+    static let horizontalIntentRatio: CGFloat = 1.35
+
+    static func shouldBegin(velocityX: CGFloat, velocityY: CGFloat) -> Bool {
+        let horizontalSpeed = abs(velocityX)
+        return velocityX < 0
+            && horizontalSpeed >= minimumHorizontalVelocity
+            && horizontalSpeed >= abs(velocityY) * horizontalIntentRatio
+    }
+
+    static func width(translationX: CGFloat) -> CGFloat {
+        min(maximumWidth, max(0, -translationX))
+    }
+}
+
+@MainActor
+private final class FeatureTimestampRevealState: ObservableObject {
+    @Published var width: CGFloat = 0
+}
+
+private struct FeatureTimestampRevealMessageView: View {
+    let message: FeatureMessage
+    @ObservedObject var reveal: FeatureTimestampRevealState
+
+    var body: some View {
+        ZStack(alignment: .topTrailing) {
+            FeatureMessageView(message: message)
+
+            if message.createdAt != .distantPast {
+                Text(message.createdAt, format: .dateTime.hour().minute())
+                    .font(T3Typography.supporting.monospacedDigit())
+                    .foregroundStyle(T3Colors.textTertiary)
+                    .lineLimit(1)
+                    .minimumScaleFactor(0.7)
+                    .dynamicTypeSize(.small ... .accessibility1)
+                    .frame(
+                        width: TranscriptTimestampRevealGeometry.maximumWidth,
+                        alignment: .trailing
+                    )
+                    .padding(.vertical, 5)
+                    .background(T3Colors.surface, in: Capsule())
+                    .frame(width: reveal.width, alignment: .trailing)
+                    .clipped()
+                    .opacity(reveal.width > 0 ? 1 : 0)
+                    .accessibilityHidden(true)
+            }
+        }
+    }
+}
+
 private struct FeatureLoadEarlierTurnsButton: View {
     let isLoading: Bool
     let onLoad: () -> Void
@@ -1532,6 +1673,7 @@ struct FeatureMessageView: View {
             .accessibilityLabel("You")
             .accessibilityValue(accessibilityValue)
             .accessibilityIdentifier("message-\(message.id)")
+            .modifier(FeatureMessageTimestampAccessibilityModifier(message: message))
         case .assistant:
             VStack(alignment: .leading, spacing: 10) {
                 if message.state == .streaming {
@@ -1553,6 +1695,7 @@ struct FeatureMessageView: View {
             }
             .frame(maxWidth: .infinity, alignment: .leading)
             .accessibilityIdentifier("message-\(message.id)")
+            .modifier(FeatureMessageTimestampAccessibilityModifier(message: message))
         case .tool:
             DisclosureGroup {
                 Text(message.text)
@@ -1569,12 +1712,14 @@ struct FeatureMessageView: View {
             .padding(.vertical, 6)
             .frame(minHeight: T3Metrics.minimumTapTarget)
             .accessibilityIdentifier("message-\(message.id)")
+            .modifier(FeatureMessageTimestampAccessibilityModifier(message: message))
         case .system:
             Text(message.text)
                 .font(T3Typography.supporting)
                 .foregroundStyle(T3Colors.textSecondary)
                 .frame(maxWidth: .infinity, alignment: .center)
                 .accessibilityIdentifier("message-\(message.id)")
+                .modifier(FeatureMessageTimestampAccessibilityModifier(message: message))
         }
     }
 
@@ -1589,6 +1734,31 @@ struct FeatureMessageView: View {
     }
 }
 
+private struct FeatureMessageTimestampAccessibilityModifier: ViewModifier {
+    let message: FeatureMessage
+
+    @ViewBuilder
+    func body(content: Content) -> some View {
+        if message.createdAt == .distantPast {
+            content
+        } else {
+            content.accessibilityCustomContent(
+                Text(accessibilityLabel),
+                Text(message.createdAt.formatted(date: .omitted, time: .shortened)),
+                importance: .default
+            )
+        }
+    }
+
+    private var accessibilityLabel: String {
+        switch message.role {
+        case .user: "Sent"
+        case .assistant: "Received"
+        case .tool, .system: "Timestamp"
+        }
+    }
+}
+
 private struct FeatureMessageAttachmentsView: View {
     let attachments: [FeatureMessageAttachment]
     @State private var previewedAttachment: FeatureMessageAttachment?

apps/swift-ios/Tests/FeatureTests/TranscriptViewportGeometryTests.swift

@@ -1,8 +1,41 @@
 import Testing
 @testable import T3Code
 
-@Suite("Transcript viewport anchoring")
+@Suite("Transcript viewport and timestamp gestures")
 struct TranscriptViewportGeometryTests {
+    @Test
+    func timestampRevealTracksLeftwardDragWithinBounds() {
+        #expect(TranscriptTimestampRevealGeometry.width(translationX: -32) == 32)
+    }
+
+    @Test
+    func timestampRevealClampsAtRestAndMaximumWidth() {
+        #expect(TranscriptTimestampRevealGeometry.width(translationX: 24) == 0)
+        #expect(
+            TranscriptTimestampRevealGeometry.width(translationX: -200)
+                == TranscriptTimestampRevealGeometry.maximumWidth
+        )
+    }
+
+    @Test
+    func timestampRevealClaimsOnlyDeliberateLeftwardHorizontalPans() {
+        #expect(
+            TranscriptTimestampRevealGeometry.shouldBegin(velocityX: -240, velocityY: 40)
+        )
+        #expect(
+            !TranscriptTimestampRevealGeometry.shouldBegin(velocityX: -40, velocityY: 240)
+        )
+        #expect(
+            !TranscriptTimestampRevealGeometry.shouldBegin(velocityX: 240, velocityY: 40)
+        )
+        #expect(
+            !TranscriptTimestampRevealGeometry.shouldBegin(velocityX: -40, velocityY: 2)
+        )
+        #expect(
+            !TranscriptTimestampRevealGeometry.shouldBegin(velocityX: -120, velocityY: 100)
+        )
+    }
+
     @Test
     func firstLoadedTranscriptAnchorsToLatestMessage() {
         let empty = TranscriptViewportGeometry(

docs/user/swiftui-thread-transcript.md

@@ -0,0 +1,6 @@
+# Native iPhone thread transcript
+
+In the native iPhone app, swipe left across the transcript to reveal the time on each message.
+The gesture requires a deliberate horizontal swipe so ordinary vertical scrolling and text
+selection keep their normal behavior. VoiceOver exposes the same time as custom content on each
+message without requiring the gesture.