use scroll view delegate to watch scroll changes and update nav bar visibility

apple/OmnivoreKit/Sources/Views/Article/WebAppView.swift

@@ -10,6 +10,7 @@ import WebKit
     let rawAuthCookie: String?
     let openLinkAction: (URL) -> Void
     let webViewActionHandler: (WKScriptMessage) -> Void
+    let navBarVisibilityRatioUpdater: (Double) -> Void
     @Binding var annotation: String
     @Binding var annotationSaveTransactionID: UUID?
     @Binding var sendIncreaseFontSignal: Bool
@@ -33,6 +34,7 @@ import WebKit
       webView.isOpaque = false
       webView.backgroundColor = UIColor.clear
       webView.configuration.userContentController = contentController
+      webView.scrollView.delegate = context.coordinator
 
       for action in WebViewAction.allCases {
         webView.configuration.userContentController.add(context.coordinator, name: action.rawValue)
@@ -53,6 +55,7 @@ import WebKit
 
       context.coordinator.linkHandler = openLinkAction
       context.coordinator.webViewActionHandler = webViewActionHandler
+      context.coordinator.updateNavBarVisibilityRatio = navBarVisibilityRatioUpdater
 
       return webView
     }

apple/OmnivoreKit/Sources/Views/Article/WebAppViewCoordinator.swift

@@ -1,6 +1,4 @@
-// import Models
 import SwiftUI
-// import Utils
 import WebKit
 
 final class WebAppViewCoordinator: NSObject {
@@ -8,6 +6,10 @@ final class WebAppViewCoordinator: NSObject {
   var linkHandler: (URL) -> Void = { _ in }
   var needsReload = true
   var lastSavedAnnotationID: UUID?
+  var updateNavBarVisibilityRatio: (Double) -> Void = { _ in }
+  private var yOffsetAtStartOfDrag: Double?
+  private var lastYOffset: Double = 0
+  private var hasDragged = false
 
   override init() {
     super.init()
@@ -34,6 +36,44 @@ extension WebAppViewCoordinator: WKNavigationDelegate {
   }
 }
 
+extension WebAppViewCoordinator: UIScrollViewDelegate {
+  func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
+    hasDragged = true
+    yOffsetAtStartOfDrag = scrollView.contentOffset.y
+  }
+
+  func scrollViewDidScroll(_ scrollView: UIScrollView) {
+    guard hasDragged else { return }
+
+    let yOffset = scrollView.contentOffset.y
+
+    if yOffset <= 0 {
+      updateNavBarVisibilityRatio(1)
+      return
+    }
+
+    if yOffset < 30 {
+      updateNavBarVisibilityRatio(1) // yOffset / 30)
+      return
+    }
+
+    guard let yOffsetAtStartOfDrag = yOffsetAtStartOfDrag else { return }
+
+    if yOffset > yOffsetAtStartOfDrag {
+      let translation = yOffset - yOffsetAtStartOfDrag
+      let ratio = 0.0 // translation < 30 ? translation / 30 : 0
+      updateNavBarVisibilityRatio(ratio)
+    }
+  }
+
+  func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
+    if decelerate, scrollView.contentOffset.y < (yOffsetAtStartOfDrag ?? 0) {
+      updateNavBarVisibilityRatio(1)
+    }
+    yOffsetAtStartOfDrag = nil
+  }
+}
+
 struct WebViewConfig {
   let url: URL
   let themeId: String

apple/OmnivoreKit/Sources/Views/Article/WebAppWrapperView.swift

@@ -35,9 +35,11 @@ public struct WebAppWrapperView: View {
   @State private var annotation = String()
   @State var annotationSaveTransactionID: UUID?
   @State var safariWebLink: SafariWebLink?
+  let navBarVisibilityRatioUpdater: (Double) -> Void
 
-  public init(viewModel: WebAppWrapperViewModel) {
+  public init(viewModel: WebAppWrapperViewModel, navBarVisibilityRatioUpdater: ((Double) -> Void)? = nil) {
     self.viewModel = viewModel
+    self.navBarVisibilityRatioUpdater = navBarVisibilityRatioUpdater ?? { _ in }
   }
 
   public var body: some View {
@@ -53,6 +55,7 @@ public struct WebAppWrapperView: View {
         #endif
       },
       webViewActionHandler: webViewActionHandler,
+      navBarVisibilityRatioUpdater: navBarVisibilityRatioUpdater,
       annotation: $annotation,
       annotationSaveTransactionID: $annotationSaveTransactionID,
       sendIncreaseFontSignal: $viewModel.sendIncreaseFontSignal,

apple/OmnivoreKit/Sources/Views/LinkedItemDetail/LinkItemDetailView.swift

@@ -25,8 +25,11 @@ public final class LinkItemDetailViewModel: ObservableObject {
 }
 
 public struct LinkItemDetailView: View {
+  @Environment(\.presentationMode) var presentationMode: Binding<PresentationMode>
+
   @ObservedObject private var viewModel: LinkItemDetailViewModel
   @State private var showFontSizePopover = false
+  @State private var navBarVisibilityRatio = 1.0
 
   public init(viewModel: LinkItemDetailViewModel) {
     self.viewModel = viewModel
@@ -51,12 +54,69 @@ public struct LinkItemDetailView: View {
   }
 
   public var body: some View {
-    innerBody
     #if os(iOS)
-      .navigationBarTitleDisplayMode(.inline)
+      if UIDevice.isIPhone, !viewModel.item.isPDF {
+        compactInnerBody
+      } else {
+        innerBody
+      }
+    #else
+      innerBody
     #endif
   }
 
+  @ViewBuilder private var compactInnerBody: some View {
+    VStack {
+      withAnimation {
+        HStack(alignment: .center) {
+          Button(
+            action: { self.presentationMode.wrappedValue.dismiss() },
+            label: {
+              Image(systemName: "chevron.backward")
+                .font(.appTitleThree)
+                .foregroundColor(.appGrayTextContrast)
+                .padding(.horizontal)
+                .padding(.bottom, 5)
+            }
+          )
+          Spacer()
+          Button(
+            action: { showFontSizePopover = true },
+            label: {
+              Image(systemName: "textformat.size")
+            }
+          )
+          .padding(.horizontal)
+          #if os(iOS)
+            .fittedPopover(isPresented: $showFontSizePopover) {
+              FontSizeAdjustmentPopoverView(
+                increaseFontAction: { viewModel.webAppWrapperViewModel?.sendIncreaseFontSignal = true },
+                decreaseFontAction: { viewModel.webAppWrapperViewModel?.sendDecreaseFontSignal = true }
+              )
+            }
+          #endif
+        }
+        .scaleEffect(x: 1, y: navBarVisibilityRatio)
+        .frame(height: 30 * navBarVisibilityRatio)
+      }
+      if let webAppWrapperViewModel = viewModel.webAppWrapperViewModel {
+        WebAppWrapperView(
+          viewModel: webAppWrapperViewModel,
+          navBarVisibilityRatioUpdater: {
+            print($0)
+            navBarVisibilityRatio = $0
+          }
+        )
+      } else {
+        Spacer()
+          .onAppear {
+            viewModel.performActionSubject.send(.load)
+          }
+      }
+    }
+    .navigationBarHidden(true)
+  }
+
   @ViewBuilder private var innerBody: some View {
     if let pdfURL = viewModel.item.pdfURL {
       #if os(iOS)