Create a NavigationTabCoordinator to manage a TabView.

ElementX/Sources/Application/Navigation/NavigationTabCoordinator.swift

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+//
+// Copyright 2025 New Vector Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+// Please see LICENSE files in the repository root for full details.
+//
+
+import Compound
+import SwiftUI
+
+/// Class responsible for displaying an arbitrary number of coordinators within the tab bar.
+@Observable class NavigationTabCoordinator: CoordinatorProtocol, CustomStringConvertible {
+    struct Tab {
+        let coordinator: CoordinatorProtocol
+        let title: String
+        let icon: KeyPath<CompoundIcons, Image>
+        let selectedIcon: KeyPath<CompoundIcons, Image>
+    }
+    
+    fileprivate struct TabModule: Identifiable {
+        let module: NavigationModule
+        let title: String
+        let icon: KeyPath<CompoundIcons, Image>
+        let selectedIcon: KeyPath<CompoundIcons, Image>
+        
+        var id: ObjectIdentifier { module.id }
+        @MainActor var coordinator: CoordinatorProtocol? { module.coordinator }
+    }
+    
+    fileprivate var tabModules = [TabModule]() {
+        didSet {
+            let diffs = tabModules.map(\.module).difference(from: oldValue.map(\.module))
+            diffs.forEach { change in
+                switch change {
+                case .insert(_, let module, _):
+                    logPresentationChange("Set tab", module)
+                    module.coordinator?.start()
+                case .remove(_, let module, _):
+                    logPresentationChange("Remove tab", module)
+                    module.tearDown()
+                }
+            }
+        }
+    }
+    
+    /// The current set of coordinators displayed by the tabs.
+    var tabCoordinators: [any CoordinatorProtocol] {
+        tabModules.compactMap(\.module.coordinator)
+    }
+    
+    /// Updates the displayed tabs with the provided array.
+    func setTabs(_ tabs: [Tab], animated: Bool = true) {
+        var transaction = Transaction()
+        transaction.disablesAnimations = !animated
+        
+        withTransaction(transaction) {
+            tabModules = tabs.map { TabModule(module: .init($0.coordinator), title: $0.title, icon: $0.icon, selectedIcon: $0.selectedIcon) }
+        }
+    }
+    
+    // MARK: - CoordinatorProtocol
+    
+    func toPresentable() -> AnyView {
+        AnyView(NavigationTabCoordinatorView(navigationTabCoordinator: self))
+    }
+    
+    // MARK: - CustomStringConvertible
+    
+    var description: String {
+        guard !tabModules.isEmpty else { return "NavigationTabCoordinator(Empty)" }
+        return "NavigationTabCoordinator(\(tabCoordinators)"
+    }
+    
+    // MARK: - Private
+    
+    private func logPresentationChange(_ change: String, _ module: NavigationModule) {
+        if let coordinator = module.coordinator {
+            MXLog.info("\(self) \(change): \(coordinator)")
+        }
+    }
+}
+
+private struct NavigationTabCoordinatorView: View {
+    @Bindable var navigationTabCoordinator: NavigationTabCoordinator
+    @State private var selectedTab: ObjectIdentifier?
+    
+    var body: some View {
+        TabView(selection: $selectedTab) {
+            ForEach(navigationTabCoordinator.tabModules) { module in
+                module.coordinator?.toPresentable()
+                    .tabItem {
+                        Label {
+                            Text(module.title)
+                        } icon: {
+                            CompoundIcon(module.id == selectedTab ? module.selectedIcon : module.icon)
+                        }
+                    }
+                    .tag(module.id)
+                    .id(module.id)
+            }
+        }
+    }
+}