iOS client for Grain
grain.social
ios
photography
atproto
feat: smooth drag-to-dismiss for story viewer with prefetch
Use UIKit UIPanGestureRecognizer for buttery smooth drag-to-dismiss,
bypassing SwiftUI's rendering pipeline. Fade-out dismiss animation
for both drag and auto-advance. Prefetch next author's stories for
instant transitions between authors.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
+285
-48
+198
Grain/Views/Stories/DragToDismiss.swift
+198
Grain/Views/Stories/DragToDismiss.swift
···
1
+
import SwiftUI
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/// Shared handle so StoryViewer can trigger a fade-dismiss programmatically
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/// (e.g. when all stories finish) using the same UIKit path as the drag gesture.
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@MainActor
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final class FadeDismissHandle {
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fileprivate weak var targetView: UIView?
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fileprivate var performDismiss: (() -> Void)?
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func fadeDismiss() {
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guard let view = targetView else {
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performDismiss?()
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return
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}
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UIView.animate(withDuration: 0.2, delay: 0, options: .curveEaseOut, animations: {
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view.alpha = 0
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view.transform = CGAffineTransform(scaleX: 0.92, y: 0.92)
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}) { _ in
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if let vc = view.findViewController(),
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let presented = vc.presentedViewController ?? (vc.isBeingPresented ? vc : nil) {
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presented.dismiss(animated: false) {
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view.alpha = 1
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view.transform = .identity
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self.performDismiss?()
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}
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} else {
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view.isHidden = true
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self.performDismiss?()
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}
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}
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}
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}
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/// Installs a UIKit UIPanGestureRecognizer on the hosting view controller's view
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/// and applies CGAffineTransform directly — bypassing SwiftUI's rendering pipeline
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/// for buttery smooth drag-to-dismiss.
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struct DragToDismissInstaller: UIViewRepresentable {
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let handle: FadeDismissHandle
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let onDismiss: () -> Void
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let onDragStart: () -> Void
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let onDragCancel: () -> Void
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let onSwipeLeft: () -> Void
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let onSwipeRight: () -> Void
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func makeUIView(context: Context) -> UIView {
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let view = UIView(frame: .zero)
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view.backgroundColor = .clear
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view.isUserInteractionEnabled = false
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context.coordinator.anchorView = view
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DispatchQueue.main.async {
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context.coordinator.installGestureIfNeeded()
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}
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return view
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}
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func updateUIView(_ uiView: UIView, context: Context) {
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context.coordinator.onDismiss = onDismiss
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context.coordinator.onDragStart = onDragStart
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context.coordinator.onDragCancel = onDragCancel
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context.coordinator.onSwipeLeft = onSwipeLeft
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context.coordinator.onSwipeRight = onSwipeRight
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handle.performDismiss = onDismiss
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}
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func makeCoordinator() -> Coordinator {
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Coordinator(
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handle: handle,
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onDismiss: onDismiss,
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onDragStart: onDragStart,
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onDragCancel: onDragCancel,
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onSwipeLeft: onSwipeLeft,
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onSwipeRight: onSwipeRight
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)
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}
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private enum DragDirection {
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case none, vertical, horizontal
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}
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final class Coordinator: NSObject, UIGestureRecognizerDelegate {
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let handle: FadeDismissHandle
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var onDismiss: () -> Void
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var onDragStart: () -> Void
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var onDragCancel: () -> Void
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var onSwipeLeft: () -> Void
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var onSwipeRight: () -> Void
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weak var anchorView: UIView?
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private weak var targetView: UIView?
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private var panGesture: UIPanGestureRecognizer?
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private var direction: DragDirection = .none
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init(handle: FadeDismissHandle, onDismiss: @escaping () -> Void, onDragStart: @escaping () -> Void, onDragCancel: @escaping () -> Void, onSwipeLeft: @escaping () -> Void, onSwipeRight: @escaping () -> Void) {
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self.handle = handle
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self.onDismiss = onDismiss
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self.onDragStart = onDragStart
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self.onDragCancel = onDragCancel
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self.onSwipeLeft = onSwipeLeft
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self.onSwipeRight = onSwipeRight
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}
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func installGestureIfNeeded() {
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guard panGesture == nil, let anchor = anchorView else { return }
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guard let vc = anchor.findViewController() else { return }
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let target = vc.view!
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targetView = target
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handle.targetView = target
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handle.performDismiss = onDismiss
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let pan = UIPanGestureRecognizer(target: self, action: #selector(handlePan))
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pan.delegate = self
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target.addGestureRecognizer(pan)
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panGesture = pan
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}
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// Allow SwiftUI tap gestures to work simultaneously
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func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith other: UIGestureRecognizer) -> Bool {
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return !(other is UIPanGestureRecognizer)
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}
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@objc private func handlePan(_ gesture: UIPanGestureRecognizer) {
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guard let view = targetView else { return }
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let translation = gesture.translation(in: view.superview ?? view)
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let velocity = gesture.velocity(in: view.superview ?? view)
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switch gesture.state {
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case .began:
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direction = .none
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case .changed:
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// Lock direction after enough movement
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if direction == .none {
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let absX = abs(translation.x)
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let absY = abs(translation.y)
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if absX > 15 || absY > 15 {
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if absY > absX && translation.y > 0 {
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direction = .vertical
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onDragStart()
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} else if absX > absY {
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direction = .horizontal
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}
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}
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}
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if direction == .vertical {
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let ty = max(translation.y, 0)
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let progress = min(ty / 300, 1)
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let scale = 1 - progress * 0.1
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view.transform = CGAffineTransform(translationX: 0, y: ty)
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.scaledBy(x: scale, y: scale)
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view.layer.cornerRadius = progress * 24
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view.clipsToBounds = true
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}
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case .ended, .cancelled:
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if direction == .vertical {
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let ty = max(translation.y, 0)
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let dismissThreshold = view.bounds.height * 0.35
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if ty > dismissThreshold || velocity.y > 1200 {
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handle.fadeDismiss()
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} else {
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// Spring back
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UIView.animate(withDuration: 0.35, delay: 0, usingSpringWithDamping: 0.85, initialSpringVelocity: 0, options: [.allowUserInteraction]) {
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view.transform = .identity
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view.layer.cornerRadius = 0
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view.clipsToBounds = false
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}
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onDragCancel()
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}
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} else if direction == .horizontal {
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if translation.x < -80 || velocity.x < -500 {
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onSwipeLeft()
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} else if translation.x > 80 || velocity.x > 500 {
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onSwipeRight()
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}
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}
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direction = .none
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default:
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break
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}
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}
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}
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}
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private extension UIView {
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func findViewController() -> UIViewController? {
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var responder: UIResponder? = self
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while let next = responder?.next {
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if let vc = next as? UIViewController {
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return vc
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}
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responder = next
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}
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return nil
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}
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}
+87
-48
Grain/Views/Stories/StoryViewer.swift
+87
-48
Grain/Views/Stories/StoryViewer.swift
···
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@State private var reportStoryCid = ""
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@State private var lastNavTime: Date = .distantPast
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@State private var labelRevealed = false
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@State private var fadeDismissHandle = FadeDismissHandle()
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@State private var prefetchedStories: [String: [GrainStory]] = [:]
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init(authors: [GrainStoryAuthor], startIndex: Int = 0, startAuthorDid: String? = nil, client: XRPCClient, onProfileTap: ((String) -> Void)? = nil, onDismiss: (() -> Void)? = nil) {
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self.authors = authors
···
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}
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var body: some View {
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storyContent
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.background(
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DragToDismissInstaller(
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handle: fadeDismissHandle,
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onDismiss: { onDismiss?() },
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onDragStart: { timer.stop() },
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onDragCancel: {
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let lr = storyLabelResult
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if lr.action == .none || lr.action == .badge { timer.start() }
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},
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onSwipeLeft: { goToNextAuthor() },
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onSwipeRight: { goToPreviousAuthor() }
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)
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)
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.statusBarHidden()
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.confirmationDialog("Delete this story?", isPresented: $showDeleteConfirm, titleVisibility: .visible) {
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Button("Delete", role: .destructive) {
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if let story = currentStory {
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Task { await deleteStory(story) }
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}
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}
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Button("Cancel", role: .cancel) {
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timer.start()
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}
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}
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.fullScreenCover(isPresented: $showReportSheet) {
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ReportView(client: client, subjectUri: reportStoryUri, subjectCid: reportStoryCid)
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.environment(auth)
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}
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.onChange(of: showReportSheet) {
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if !showReportSheet {
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timer.start()
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}
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}
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.task {
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timer.onComplete = { [self] in goToNext() }
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timer.onHalfway = { [self] in markCurrentStoryViewed() }
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await loadStoriesForCurrentAuthor()
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}
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}
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@ViewBuilder
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private var storyContent: some View {
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ZStack {
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Color.black.ignoresSafeArea()
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···
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.frame(maxWidth: .infinity)
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}
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}
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.simultaneousGesture(
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DragGesture(minimumDistance: 80)
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.onEnded { value in
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if value.translation.width < -80 {
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goToNextAuthor()
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} else if value.translation.width > 80 {
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goToPreviousAuthor()
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}
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}
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)
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}
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.allowsHitTesting(!showReportSheet && !showDeleteConfirm && (labelRevealed || storyLabelResult.action == .none || storyLabelResult.action == .badge))
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// Header overlay (on top of tap zones)
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// Header overlay
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VStack(spacing: 0) {
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StoryProgressBars(timer: timer, stories: stories, currentStoryIndex: currentStoryIndex)
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.padding(.horizontal)
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.padding(.top, 8)
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// Creator info + actions
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HStack(alignment: .center) {
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Button {
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close()
···
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Spacer()
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.allowsHitTesting(false)
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// Location pill
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if let locationText = storyLocationText(story) {
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HStack {
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HStack(spacing: 4) {
···
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.tint(.white)
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}
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}
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.statusBarHidden()
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.confirmationDialog("Delete this story?", isPresented: $showDeleteConfirm, titleVisibility: .visible) {
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Button("Delete", role: .destructive) {
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if let story = currentStory {
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Task { await deleteStory(story) }
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}
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}
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Button("Cancel", role: .cancel) {
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timer.start()
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}
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}
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.fullScreenCover(isPresented: $showReportSheet) {
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ReportView(client: client, subjectUri: reportStoryUri, subjectCid: reportStoryCid)
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.environment(auth)
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}
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.onChange(of: showReportSheet) {
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if !showReportSheet {
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timer.start()
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}
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}
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.task {
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timer.onComplete = { [self] in goToNext() }
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timer.onHalfway = { [self] in markCurrentStoryViewed() }
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await loadStoriesForCurrentAuthor()
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}
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}
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280
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// MARK: - Navigation
281
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private func close() {
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timer.stop()
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onDismiss?()
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fadeDismissHandle.fadeDismiss()
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}
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private func goToNext() {
···
320
328
private func goToNextAuthor() {
321
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if currentAuthorIndex < authors.count - 1 {
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currentAuthorIndex += 1
323
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currentStoryIndex = 0
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stories = []
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isLoadingStories = true
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timer.stop()
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Task { await loadStoriesForCurrentAuthor() }
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switchToCurrentAuthor()
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} else {
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close()
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}
···
333
337
private func goToPreviousAuthor() {
334
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if currentAuthorIndex > 0 {
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currentAuthorIndex -= 1
340
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switchToCurrentAuthor()
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}
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}
343
+
344
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private func switchToCurrentAuthor() {
345
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timer.stop()
346
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let did = authors[currentAuthorIndex].profile.did
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if let cached = prefetchedStories.removeValue(forKey: did) {
348
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stories = cached
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currentStoryIndex = viewedStories.firstUnviewedIndex(in: cached)
350
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labelRevealed = false
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isLoadingStories = false
352
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let lr = storyLabelResult
353
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if lr.action == .none || lr.action == .badge { timer.start() }
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prefetchAdjacentAuthors()
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} else {
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currentStoryIndex = 0
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stories = []
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isLoadingStories = true
339
-
timer.stop()
340
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Task { await loadStoriesForCurrentAuthor() }
341
360
}
342
361
}
···
350
369
timer.stop()
351
370
352
371
do {
353
-
let response = try await client.getStories(actor: did, auth: auth.authContext())
354
-
stories = response.stories
355
-
currentStoryIndex = viewedStories.firstUnviewedIndex(in: response.stories)
372
+
let fetched: [GrainStory]
373
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if let cached = prefetchedStories.removeValue(forKey: did) {
374
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fetched = cached
375
+
} else {
376
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fetched = try await client.getStories(actor: did, auth: auth.authContext()).stories
377
+
}
378
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stories = fetched
379
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currentStoryIndex = viewedStories.firstUnviewedIndex(in: fetched)
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380
labelRevealed = false
357
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let lr = storyLabelResult
358
382
if lr.action == .none || lr.action == .badge {
···
362
386
stories = []
363
387
}
364
388
isLoadingStories = false
389
+
390
+
// Prefetch next author's stories
391
+
prefetchAdjacentAuthors()
392
+
}
393
+
394
+
private func prefetchAdjacentAuthors() {
395
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let nextIndex = currentAuthorIndex + 1
396
+
guard nextIndex < authors.count else { return }
397
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let did = authors[nextIndex].profile.did
398
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guard prefetchedStories[did] == nil else { return }
399
+
Task {
400
+
if let response = try? await client.getStories(actor: did, auth: auth.authContext()) {
401
+
prefetchedStories[did] = response.stories
402
+
}
403
+
}
365
404
}
366
405
367
406
private func markCurrentStoryViewed() {