HTML rendering support for the Website service (#5)

This PR contains the work done to replace the use of static _HTML_ files with type-safe HTML rendered server-side via **Elementary** through **Hummingbird**.

To provide further details about the work done:

* Added the **Elementary** dependencies.
* Added the `IndexPage` and `ErrorPage` pages, ported from the old HTML boilerplate; removed the static files.
* Added the `RootController` controller serving GET / using the `IndexPage` page, wired into the router.
* Reworked the `NotFoundMiddleware` middleare to render `ErrorPage` page directly; non-notFound errors still propagate.
* the `FileMiddleware` middleware no longer searches for any static `index.html` file.
* Simplified the `StaticFile` enumeration, dropped unused constants and now-unnecessary throws.

Reviewed-on: rock-n-code/loud-amsterdam#5
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Services/Website/Sources/Library/Public/Middlewares/NotFoundMiddleware.swift

@@ -1,46 +1,19 @@
-import Foundation
+import Elementary
 import Hummingbird
-import NIOCore
+import HummingbirdElementary
 
 /// Serves a custom error page for requests that match neither a route nor a static file.
 ///
 /// Placed ahead of `FileMiddleware` in the middleware chain, it catches the `.notFound` error
-/// that bubbles up when no file exists for the requested path and responds with the preloaded
-/// error page and a `404 Not Found` status.
+/// that bubbles up when no file exists for the requested path and responds with the rendered
+/// ``ErrorPage`` and a `404 Not Found` status.
 public struct NotFoundMiddleware<Context: RequestContext> {
-    
-    // MARK: Properties
-    
-    /// The body of the error page served on a not-found response.
-    private let page: ByteBuffer
-    
+
     // MARK: Initializers
-    
-    /// Creates a middleware that serves the error page (`404.html`) from the static files folder.
-    ///
-    /// The page is read once, at construction. A minimal fallback body is used when the file is
-    /// missing.
-    /// - Parameter staticFilesPath: the folder, relative to the working directory, the static files are served from.
-    public init(
-        _ staticFilesPath: String
-    ) {
-        let path = StaticFile.errorHTML.path(relativeTo: staticFilesPath)
-        
-        if let data = try? Data(contentsOf: URL(fileURLWithPath: path)) {
-            self.init(page: .init(bytes: data))
-        } else {
-            self.init(page: .init(string: "404 Not Found"))
-        }
-    }
-    
-    /// Creates a middleware that serves the given error page on a not-found response.
-    /// - Parameter page: the body of the error page.
-    init(
-        page: ByteBuffer
-    ) {
-        self.page = page
-    }
-    
+
+    /// Creates a not-found middleware.
+    public init() {}
+
 }
 
 // MARK: - RouterMiddleware
@@ -49,6 +22,16 @@ extension NotFoundMiddleware: RouterMiddleware {
 
     // MARK: Functions
 
+    /// Passes the request down the chain, rendering the error page if it results in a not-found
+    /// response.
+    ///
+    /// Any error other than `.notFound` is rethrown unchanged.
+    /// - Parameters:
+    ///   - request: the incoming request.
+    ///   - context: the context the request is resolved against.
+    ///   - next: the next responder in the middleware chain.
+    /// - Returns: the downstream response, or the rendered ``ErrorPage`` with a `404 Not Found` status.
+    /// - Throws: any non-not-found error thrown downstream.
     public func handle(
         _ request: Request,
         context: Context,
@@ -57,7 +40,6 @@ extension NotFoundMiddleware: RouterMiddleware {
         do {
             return try await next(request, context)
         } catch let error {
-            // Only intercept "not found"; let every other error propagate.
             guard
                 let responseError = error as? any HTTPResponseError,
                 responseError.status == .notFound
@@ -65,14 +47,14 @@ extension NotFoundMiddleware: RouterMiddleware {
                 throw error
             }
 
-            var headers = HTTPFields()
-
-            headers[.contentType] = StaticFile.errorHTML.contentType
-
-            return Response(
-                status: .notFound,
-                headers: headers,
-                body: .init(byteBuffer: page)
+            return HTMLResponse(
+                status: .notFound
+            ) {
+                ErrorPage()
+            }
+            .response(
+                from: request,
+                context: context
             )
         }
     }