wikimedia · mazevedofs · Jan 13, 2023 · Jan 6, 2023 · Jan 6, 2023 · Jan 6, 2023
diff --git a/WMF Framework/Theme.swift b/WMF Framework/Theme.swift
@@ -696,7 +696,6 @@ public class Colors: NSObject {
     }
 }
 
-
 @objc(WMFTheme)
 public class Theme: NSObject {
 
@@ -894,3 +893,12 @@ public protocol Themeable: AnyObject {
     @objc(applyTheme:)
     func apply(theme: Theme) // this might be better as a var theme: Theme { get set } - common VC superclasses could check for viewIfLoaded and call an update method in the setter. This would elminate the need for the viewIfLoaded logic in every applyTheme:
 }
+
+// Use for SwiftUI environment objects
+public final class ObservableTheme: ObservableObject {
+    @Published public var theme: Theme
+
+    public init(theme: Theme) {
+        self.theme = theme
+    }
+}
diff --git a/Wikipedia.xcodeproj/project.pbxproj b/Wikipedia.xcodeproj/project.pbxproj
diff --git a/Wikipedia/Code/DemoShiftingThreeLineHeaderView.swift b/Wikipedia/Code/DemoShiftingThreeLineHeaderView.swift
@@ -0,0 +1,80 @@
+import UIKit
+
+class DemoShiftingThreeLineHeaderView: ShiftingTopView, Themeable {
+
+    private(set) var theme: Theme
+
+    private lazy var headerView: ThreeLineHeaderView = {
+        let view = ThreeLineHeaderView()
+        view.topSmallLine.text = "Test 1"
+        view.middleLargeLine.text = "Test 2"
+        view.bottomSmallLine.text = "Test 3"
+        view.translatesAutoresizingMaskIntoConstraints = false
+        return view
+    }()
+
+    private var topConstraint: NSLayoutConstraint?
+
+    init(shiftOrder: Int, theme: Theme) {
+        self.theme = theme
+        super.init(shiftOrder: shiftOrder)
+    }
+
+    required init?(coder aDecoder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+
+    override func setup() {
+        super.setup()
+
+        addSubview(headerView)
+
+        let top = headerView.topAnchor.constraint(equalTo: topAnchor)
+        let bottom = bottomAnchor.constraint(equalTo: headerView.bottomAnchor)
+        let leading = headerView.leadingAnchor.constraint(equalTo: leadingAnchor)
+        let trailing = trailingAnchor.constraint(equalTo: headerView.trailingAnchor)
+
+        NSLayoutConstraint.activate([
+            top,
+            bottom,
+            leading,
+            trailing
+        ])
+
+        self.topConstraint = top
+        clipsToBounds = true
+        apply(theme: theme)
+    }
+
+    // MARK: Overrides
+
+    override var contentHeight: CGFloat {
+        return headerView.frame.height
+    }
+
+    private var isFullyHidden: Bool {
+       return -(topConstraint?.constant ?? 0) == contentHeight
+    }
+
+    override func shift(amount: CGFloat) -> ShiftingTopView.AmountShifted {
+
+        let limitedShiftAmount = max(0, min(amount, contentHeight))
+
+        let percent = limitedShiftAmount / contentHeight
+        alpha = 1.0 - percent
+
+        if (self.topConstraint?.constant ?? 0) != -limitedShiftAmount {
+            self.topConstraint?.constant = -limitedShiftAmount
+        }
+
+        return limitedShiftAmount
+    }
+
+    // MARK: Themeable
+
+    func apply(theme: Theme) {
+        self.theme = theme
+        backgroundColor = theme.colors.paperBackground
+        headerView.apply(theme: theme)
+    }
+}
diff --git a/Wikipedia/Code/ShiftingNavigationBarView.swift b/Wikipedia/Code/ShiftingNavigationBarView.swift
@@ -0,0 +1,117 @@
+import UIKit
+
+class ShiftingNavigationBarView: ShiftingTopView, Themeable {
+
+    private let navigationItems: [UINavigationItem]
+    private weak var popDelegate: UIViewController? // Navigation back actions will be forwarded to this view controller
+
+    private var topConstraint: NSLayoutConstraint?
+
+    private lazy var bar: UINavigationBar = {
+        let bar = UINavigationBar()
+        bar.translatesAutoresizingMaskIntoConstraints = false
+        bar.delegate = self
+        return bar
+    }()
+
+    init(shiftOrder: Int, navigationItems: [UINavigationItem], popDelegate: UIViewController) {
+        self.navigationItems = navigationItems
+        self.popDelegate = popDelegate
+        super.init(shiftOrder: shiftOrder)
+    }
+
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+
+    override func setup() {
+        super.setup()
+
+        bar.setItems(navigationItems, animated: false)
+        addSubview(bar)
+
+        let top = bar.topAnchor.constraint(equalTo: topAnchor)
+        let bottom = bottomAnchor.constraint(equalTo: bar.bottomAnchor)
+        let leading = bar.leadingAnchor.constraint(equalTo: leadingAnchor)
+        let trailing = trailingAnchor.constraint(equalTo: bar.trailingAnchor)
+
+        NSLayoutConstraint.activate([
+            top,
+            bottom,
+            leading,
+            trailing
+        ])
+
+        self.topConstraint = top
+
+        clipsToBounds = true
+    }
+
+    // MARK: Overrides
+
+    override var contentHeight: CGFloat {
+        return bar.frame.height
+    }
+
+    private var isFullyHidden: Bool {
+       return -(topConstraint?.constant ?? 0) == contentHeight
+    }
+
+    override func shift(amount: CGFloat) -> ShiftingTopView.AmountShifted {
+
+        // Only allow navigation bar to move just out of frame
+        let limitedShiftAmount = max(0, min(amount, contentHeight))
+
+        // Shrink and fade
+        let percent = limitedShiftAmount / contentHeight
+        let barScaleTransform = CGAffineTransformMakeScale(1.0 - (percent/2), 1.0 - (percent/2))
+        for subview in self.bar.subviews {
+            for subview in subview.subviews {
+                subview.transform = barScaleTransform
+            }
+        }
+        alpha = 1.0 - percent
+
+        // Shift Y placement
+        if (self.topConstraint?.constant ?? 0) != -limitedShiftAmount {
+            self.topConstraint?.constant = -limitedShiftAmount
+        }
+
+        return limitedShiftAmount
+    }
+
+    // MARK: Themeable
+
+    func apply(theme: Theme) {
+        bar.setBackgroundImage(theme.navigationBarBackgroundImage, for: .default)
+        bar.titleTextAttributes = theme.navigationBarTitleTextAttributes
+        bar.isTranslucent = false
+        bar.barTintColor = theme.colors.chromeBackground
+        bar.shadowImage = theme.navigationBarShadowImage
+        bar.tintColor = theme.colors.chromeText
+    }
+}
+
+// MARK: Themeable
+
+extension ShiftingNavigationBarView: UINavigationBarDelegate {
+    func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {
+        popDelegate?.navigationController?.popViewController(animated: true)
+        return false
+    }
+
+    // Taken from NavigationBar.swift
+    func navigationBar(_ navigationBar: UINavigationBar, didPop item: UINavigationItem) {
+        // During iOS 14's long press to access back history, this function is called *after* the unneeded navigationItems have been popped off.
+        // However, with our custom navBar the actual articleVC isn't changed. So we need to find the articleVC for the top navItem, and pop to it.
+        // This should be in `shouldPop`, but as of iOS 14.0, `shouldPop` isn't called when long pressing a back button. Once this is fixed by Apple,
+        // we should move this to `shouldPop` to improve animations. (Update: A bug tracker was filed w/ Apple, and this won't be fixed anytime soon.
+        // Apple: "This is expected behavior. Due to side effects that many clients have in the shouldPop handler, we do not consult it when using the back
+        // button menu. We instead recommend that you hide the back button when you wish to disallow popping past a particular point in the navigation stack.")
+        if let topNavigationItem = navigationBar.items?.last,
+           let navController = popDelegate?.navigationController,
+           let tappedViewController = navController.viewControllers.first(where: {$0.navigationItem == topNavigationItem}) {
+            popDelegate?.navigationController?.popToViewController(tappedViewController, animated: true)
+        }
+    }
+}
diff --git a/Wikipedia/Code/ShiftingScrollView.swift b/Wikipedia/Code/ShiftingScrollView.swift
@@ -0,0 +1,48 @@
+import SwiftUI
+
+struct ShiftingScrollView<Content: View>: View {
+
+    @EnvironmentObject var data: ShiftingTopViewsData
+
+    let axes: Axis.Set
+    let showsIndicators: Bool
+    let content: Content
+
+    init(
+        axes: Axis.Set = .vertical,
+        showsIndicators: Bool = true,
+        @ViewBuilder content: () -> Content
+    ) {
+        self.axes = axes
+        self.showsIndicators = showsIndicators
+        self.content = content()
+    }
+
+    var body: some View {
+        ScrollView(axes, showsIndicators: showsIndicators) {
+            ZStack(alignment:.topLeading) {
+                GeometryReader { geometry in
+                    Color.clear.preference(
+                        key: ScrollOffsetPreferenceKey.self,
+                        value: geometry.frame(in: .named("scrollView")).origin
+                    )
+                }
+                .frame(width: 0, height: 0)
+                content
+                    .padding(.top, data.totalHeight)
+            }
+        }
+        .coordinateSpace(name: "scrollView")
+        .onPreferenceChange(ScrollOffsetPreferenceKey.self, perform: offsetChanged)
+    }
+
+    func offsetChanged(_ offset: CGPoint) {
+        data.scrollAmount = -offset.y
+    }
+}
+
+private struct ScrollOffsetPreferenceKey: PreferenceKey {
+    static var defaultValue: CGPoint = .zero
+
+    static func reduce(value: inout CGPoint, nextValue: () -> CGPoint) {}
+}
diff --git a/Wikipedia/Code/ShiftingTopView.swift b/Wikipedia/Code/ShiftingTopView.swift
@@ -0,0 +1,43 @@
+import Foundation
+import CocoaLumberjackSwift
+
+class ShiftingTopView: SetupView {
+    typealias AmountShifted = CGFloat
+
+    weak var stackView: ShiftingTopViewsStack?
+    let shiftOrder: Int
+
+    init(shiftOrder: Int) {
+        self.shiftOrder = shiftOrder
+        super.init(frame: .zero)
+    }
+
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+
+    override func setup() {
+        super.setup()
+
+        translatesAutoresizingMaskIntoConstraints = false
+    }
+
+    override func layoutSubviews() {
+        super.layoutSubviews()
+
+        if stackView == nil {
+            DDLogError("Missing stackView assignment in ShiftingSubview, which could potentially cause incorrect content inset/padding calculations.")
+        }
+        stackView?.calculateTotalHeight()
+    }
+
+    var contentHeight: CGFloat {
+        assertionFailure("Must override")
+        return 0
+    }
+
+    func shift(amount: CGFloat) -> AmountShifted {
+        assertionFailure("Must override")
+        return 0
+    }
+}
diff --git a/Wikipedia/Code/ShiftingTopViewsContaining.swift b/Wikipedia/Code/ShiftingTopViewsContaining.swift
@@ -0,0 +1,65 @@
+import Foundation
+import SwiftUI
+
+protocol ShiftingTopViewsContaining: UIViewController {
+    var shiftingTopViewsStack: ShiftingTopViewsStack? { get set }
+}
+
+// Note: This subclass only seems necessary for proper nav bar hiding in iOS 14 & 15. It can be removed and switched to raw UIHostingControllers for iOS16+
+private class NavigationBarHidingHostingVC<Content: View>: UIHostingController<Content> {
+
+    override func viewWillAppear(_ animated: Bool) {
+        super.viewWillAppear(animated)
+
+        self.navigationController?.isNavigationBarHidden = true
+    }
+}
+
+extension ShiftingTopViewsContaining {
+    func setup(shiftingTopViews: [ShiftingTopView], swiftuiView: some View, observableTheme: ObservableTheme) {
+
+        navigationController?.isNavigationBarHidden = true
+
+        let shiftingTopViewsStack = ShiftingTopViewsStack()
+
+        // Add needed environment objects to SwiftUI view, then embed hosting view controller, then embed SwiftUI hosting view controller
+        let finalSwiftUIView = swiftuiView
+            .environmentObject(shiftingTopViewsStack.data)
+            .environmentObject(observableTheme)
+
+        let childHostingVC: UIViewController
+
+        if #available(iOS 16, *) {
+            childHostingVC = UIHostingController(rootView: finalSwiftUIView)
+        } else {
+            childHostingVC = NavigationBarHidingHostingVC(rootView: finalSwiftUIView)
+        }
+
+        childHostingVC.view.translatesAutoresizingMaskIntoConstraints = false
+        view.addSubview(childHostingVC.view)
+
+        NSLayoutConstraint.activate([
+            view.safeAreaLayoutGuide.topAnchor.constraint(equalTo: childHostingVC.view.topAnchor),
+            view.safeAreaLayoutGuide.leadingAnchor.constraint(equalTo: childHostingVC.view.leadingAnchor),
+            view.safeAreaLayoutGuide.trailingAnchor.constraint(equalTo: childHostingVC.view.trailingAnchor),
+            view.safeAreaLayoutGuide.bottomAnchor.constraint(equalTo: childHostingVC.view.bottomAnchor)
+        ])
+
+        addChild(childHostingVC)
+        childHostingVC.didMove(toParent: self)
+        childHostingVC.view.backgroundColor = .clear
+
+        // Add shiftingTopViewsStack
+        view.addSubview(shiftingTopViewsStack)
+
+        NSLayoutConstraint.activate([
+            view.safeAreaLayoutGuide.topAnchor.constraint(equalTo: shiftingTopViewsStack.topAnchor),
+            view.leadingAnchor.constraint(equalTo: shiftingTopViewsStack.leadingAnchor),
+            view.trailingAnchor.constraint(equalTo: shiftingTopViewsStack.trailingAnchor)
+        ])
+
+        shiftingTopViewsStack.addShiftingTopViews(shiftingTopViews)
+        shiftingTopViewsStack.apply(theme: observableTheme.theme)
+        self.shiftingTopViewsStack = shiftingTopViewsStack
+    }
+}
diff --git a/Wikipedia/Code/ShiftingTopViewsData.swift b/Wikipedia/Code/ShiftingTopViewsData.swift
@@ -0,0 +1,7 @@
+import Foundation
+import Combine
+
+class ShiftingTopViewsData: ObservableObject {
+    @Published var scrollAmount = CGFloat(0)
+    @Published var totalHeight = CGFloat(0)
+}