feat: Initial commit

Sources/CliDoc/NodeModifier.swift

@@ -0,0 +1,59 @@
+public protocol NodeModifier {
+  associatedtype Body: Node
+  // swiftlint:disable type_name
+  associatedtype _Content: Node
+  typealias Content = _Content
+  // swiftlint:enable type_name
+
+  func render(content: Content) -> Body
+}
+
+public extension NodeModifier {
+  func modifier<T: NodeModifier>(
+    _ modifier: T
+  ) -> ModifiedNode<Self, T> where T.Content == Body {
+    .init(content: self, modifier: modifier)
+  }
+}
+
+public extension Node {
+
+  func modifier<T: NodeModifier>(_ modifier: T) -> ModifiedNode<Self, T> {
+    .init(content: self, modifier: modifier)
+  }
+}
+
+public struct ModifiedNode<Content, Modifier> {
+  var content: Content
+  var modifier: Modifier
+}
+
+extension ModifiedNode: NodeRepresentable where Content: NodeRepresentable,
+  Modifier: NodeModifier,
+  Modifier.Content == Content
+{
+  public func render() -> String {
+    modifier.render(content: content).render()
+  }
+}
+
+extension ModifiedNode: Node where Content: Node,
+  Modifier: NodeModifier,
+  Modifier.Content == Content
+{
+  public var body: some Node {
+    content
+  }
+}
+
+extension ModifiedNode: NodeModifier where
+  Content: NodeModifier,
+  Modifier: NodeModifier,
+  Content.Body == Modifier.Content,
+  Content: Node
+{
+  public func render(content: Content) -> some Node {
+    let body = content.body
+    return modifier.render(content: body).render()
+  }
+}