Support <meta> and <title> in DOMFiberRenderer

Sources/TokamakCore/App/Scenes/WindowGroup.swift

@@ -15,6 +15,11 @@
 //  Created by Carson Katri on 7/16/20.
 //
 
+@_spi(TokamakCore)
+public struct _WindowGroupTitle: _PrimitiveView {
+  public let title: Text?
+}
+
 public struct WindowGroup<Content>: Scene, TitledScene where Content: View {
   public let id: String
   public let title: Text?
@@ -77,6 +82,10 @@ public struct WindowGroup<Content>: Scene, TitledScene where Content: View {
 //  }
 
   public func _visitChildren<V>(_ visitor: V) where V: SceneVisitor {
-    visitor.visit(content)
+    print("Visiting scene")
+    visitor.visit(Group {
+      _WindowGroupTitle(title: self.title)
+      content
+    })
   }
 }

Sources/TokamakCore/Fiber/Fiber.swift

@@ -423,7 +423,8 @@ public extension FiberReconciler {
           environment: .init(rootEnvironment),
           traits: .init(),
           preferenceStore: preferences
-        )
+        ),
+        preferenceStore: preferences ?? .init()
       )
       if let preferenceStore = outputs.preferenceStore {
         preferences = preferenceStore

Sources/TokamakCore/Fiber/FiberReconciler.swift

@@ -69,6 +69,10 @@ public final class FiberReconciler<Renderer: FiberRenderer> {
           .environmentValues(environment)
       }
     }
+
+    static func _makeView(_ inputs: ViewInputs<Self>) -> ViewOutputs {
+      .init(inputs: inputs, preferenceStore: inputs.preferenceStore ?? .init())
+    }
   }
 
   /// The `Layout` container for the root of a `View` hierarchy.
@@ -275,6 +279,10 @@ public final class FiberReconciler<Renderer: FiberRenderer> {
     for action in afterReconcileActions {
       action()
     }
+
+    if let preferences = current.preferences {
+      renderer.preferencesChanged(preferences)
+    }
   }
 }
 

Sources/TokamakCore/Fiber/FiberRenderer.swift

@@ -88,6 +88,9 @@ public protocol FiberRenderer {
   /// (in this case just `DuelOfTheStates` as both properties were on it),
   /// and reconcile after all changes have been collected.
   func schedule(_ action: @escaping () -> ())
+
+  /// Called by the reconciler when the preferences of the topmost `Fiber` changed.
+  func preferencesChanged(_ preferenceStore: _PreferenceStore)
 }
 
 public extension FiberRenderer {
@@ -107,6 +110,8 @@ public extension FiberRenderer {
     }
   }
 
+  func preferencesChanged(_ preferenceStore: _PreferenceStore) {}
+
   @discardableResult
   @_disfavoredOverload
   func render<V: View>(_ view: V) -> FiberReconciler<Self> {

Sources/TokamakCore/Preferences/PreferenceKey.swift

@@ -118,6 +118,19 @@ public final class _PreferenceStore: CustomDebugStringConvertible {
     _PreferenceValue(storage: previousValues[ObjectIdentifier(key)] ?? .init(key))
   }
 
+  /// Returns the new value for `Key`, or `nil` if the value did not change.
+  public func newValue<Key>(forKey key: Key.Type = Key.self) -> Key.Value?
+    where Key: PreferenceKey, Key.Value: Equatable
+  {
+    let value = value(forKey: key).value
+    let previousValue = previousValue(forKey: key).value
+    if value != previousValue {
+      return value
+    } else {
+      return nil
+    }
+  }
+
   public func insert<Key>(_ value: Key.Value, forKey key: Key.Type = Key.self)
     where Key: PreferenceKey
   {

Sources/TokamakDOM/DOMFiberRenderer.swift

@@ -323,6 +323,38 @@ public struct DOMFiberRenderer: FiberRenderer {
     }
   }
 
+  final class Head {
+    let head = document.head.object!
+    var metaTags = [JSObject]()
+    var title: JSObject?
+  }
+
+  private let head = Head()
+  public func preferencesChanged(_ preferenceStore: _PreferenceStore) {
+    if let newMetaTags = preferenceStore.newValue(forKey: HTMLMetaPreferenceKey.self) {
+      for oldTag in head.metaTags {
+        _ = head.head.removeChild!(oldTag)
+      }
+      head.metaTags = newMetaTags.map {
+        let template = document.createElement!("template").object!
+        template.innerHTML = .string($0.outerHTML())
+        let meta = template.content.firstChild.object!
+        _ = head.head.appendChild!(meta)
+        return meta
+      }
+    }
+    if let newTitle = preferenceStore.newValue(forKey: HTMLTitlePreferenceKey.self) {
+      if let title = head.title {
+        title.innerHTML = .string(newTitle)
+      } else {
+        let node = document.createElement!("title").object!
+        _ = head.head.appendChild!(node)
+        node.innerHTML = .string(newTitle)
+        head.title = node
+      }
+    }
+  }
+
   private let scheduler = JSScheduler()
   public func schedule(_ action: @escaping () -> ()) {
     scheduler.schedule(options: nil, action)

Sources/TokamakStaticHTML/Scenes/WindowGroup.swift

@@ -15,10 +15,26 @@
 //  Created by Carson Katri on 7/19/20.
 //
 
-import TokamakCore
+@_spi(TokamakCore) import TokamakCore
 
 extension WindowGroup: SceneDeferredToRenderer {
   public var deferredBody: AnyView {
     AnyView(content)
   }
 }
+
+extension _WindowGroupTitle: HTMLConvertible {
+  public var tag: String { "div" }
+  public func attributes(useDynamicLayout: Bool) -> [HTMLAttribute: String] {
+    guard !useDynamicLayout else { return [:] }
+    return ["style": "position: absolute; width: 0; height: 0; top: 0; left: 0;"]
+  }
+
+  public func primitiveVisitor<V>(useDynamicLayout: Bool) -> ((V) -> ())? where V: ViewVisitor {
+    {
+      if let title = self.title {
+        $0.visit(HTMLTitle(_TextProxy(title).rawText))
+      }
+    }
+  }
+}

Sources/TokamakStaticHTML/StaticHTMLRenderer.swift

@@ -58,7 +58,7 @@ struct HTMLBody: AnyHTML {
   ]
 }
 
-extension HTMLMeta.MetaTag {
+public extension HTMLMeta.MetaTag {
   func outerHTML() -> String {
     switch self {
     case let .charset(charset):