Adjustments to the Localization package dependency (#11)

This PR contains the work done to refactor the _Localization_ package and tidy the project a little bit.

To provider further details about the work:

* The `Negotiate` function was moved to the _Localization_ package.
* The `WebsiteRequestContext` context no longer resolves a default language at creation; it starts empty and relies on the `LocalizationMiddleware` middleware to fill it in.
* Fixed the local dependency path to Packages/Localization for the **Website** package as it only resolved inside the Xcode workspace before, breaking swift build, the Makefile, and the Docker build).
* Updated the `README` file to document language negotiation, the GET /health route, and the full middleware chain; doc comments across the moved/renamed types were brought back in sync with the code.

Reviewed-on: rock-n-code/loud-amsterdam#11
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Packages/Localization/Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:6.3
+// swift-tools-version: 6.3
 
 import PackageDescription
 

Packages/Localization/Sources/Methods/Negotiate.swift

@@ -0,0 +1,101 @@
+import Foundation
+
+/// Negotiates the best supported language for a request from its `Accept-Language` header.
+///
+/// Bound to a bundle's catalog languages via ``LanguageList``, an instance is invoked like a
+/// function — through ``callAsFunction(acceptLanguage:)`` — to resolve a header value to a
+/// supported language identifier, falling back to the default language.
+public struct Negotiate: Sendable {
+
+    // MARK: Properties
+
+    /// The supported languages and default language, derived from the bundle's String Catalog.
+    private let list: LanguageList
+
+    // MARK: Initializers
+
+    /// Creates a language negotiator backed by the given bundle's String Catalog.
+    /// - Parameter bundle: the bundle whose String Catalog defines the supported languages.
+    public init(
+        bundle: Bundle
+    ) {
+        self.list = .init(bundle: bundle)
+    }
+
+    // MARK: Methods
+
+    /// Picks the best supported language for the given `Accept-Language` header value.
+    ///
+    /// Invoked by calling the instance directly, for example `negotiate(acceptLanguage: header)`.
+    /// The header is split into its language tags (dropping any `q` weights), then matched against
+    /// the supported languages with `Bundle.preferredLocalizations(from:forPreferences:)`. When the
+    /// header is absent or matches nothing, the default language is returned.
+    /// - Parameter acceptLanguage: the raw `Accept-Language` header value, if any.
+    /// - Returns: the identifier of the supported language to serve.
+    public func callAsFunction(
+        acceptLanguage language: String?
+    ) -> String {
+        guard let language else {
+            return list.default
+        }
+
+        let tags = tags(from: language)
+
+        guard !tags.isEmpty else {
+            return list.default
+        }
+
+        let preferred = Bundle.preferredLocalizations(
+            from: list.all,
+            forPreferences: tags
+        )
+
+        return preferred.first
+            ?? list.default
+    }
+
+}
+
+// MARK: - Helpers
+
+private extension Negotiate {
+
+    // MARK: Methods
+
+    /// Extracts the ordered language tags from an `Accept-Language` header value.
+    ///
+    /// Each comma-separated entry is reduced to its language tag by dropping the `;q=` weight, and
+    /// blank entries are removed. The original order is kept, which mirrors descending preference
+    /// closely enough for `preferredLocalizations(from:forPreferences:)` to resolve correctly.
+    /// - Parameter acceptLanguage: the raw `Accept-Language` header value.
+    /// - Returns: the ordered, weight-stripped language tags.
+    func tags(
+        from acceptLanguage: String
+    ) -> [String] {
+        acceptLanguage
+            .split(separator: .Separator.comma)
+            .map { entry in
+                entry
+                    .split(separator: .Separator.semicolon)
+                    .first
+                    .map(String.init)?
+                    .trimmingCharacters(in: .whitespaces)
+                ?? .empty
+            }
+            .filter { !$0.isEmpty }
+    }
+
+}
+
+// MARK: - Constants
+
+private extension Character {
+    enum Separator {
+        static let comma: Character = ","
+        static let semicolon: Character = ";"
+    }
+}
+
+private extension String {
+    static let empty: String = ""
+}

Packages/Localization/Tests/Cases/Methods/NegotiateTests.swift

@@ -0,0 +1,78 @@
+import Foundation
+import Testing
+
+@testable import Localization
+
+@Suite("Negotiate method")
+struct NegotiateTests {
+
+    // MARK: Constants
+
+    private let negotiate = Negotiate(bundle: .module)
+
+    // MARK: Functional tests
+
+    @Test
+    func `matches an exact language tag`() {
+        let language = negotiate(acceptLanguage: "de")
+
+        #expect(language == "de")
+    }
+
+    @Test
+    func `matches a regional language tag`() {
+        let language = negotiate(acceptLanguage: "de-AT")
+
+        #expect(language == "de")
+    }
+
+    @Test
+    func `respects the header order of preference`() {
+        let language = negotiate(acceptLanguage: "de, en")
+
+        #expect(language == "de")
+    }
+
+    @Test
+    func `strips quality weights from the language tags`() {
+        let language = negotiate(acceptLanguage: "de;q=0.5, en;q=0.9")
+
+        #expect(language == "de")
+    }
+
+    @Test
+    func `trims whitespace around the language tags`() {
+        let language = negotiate(acceptLanguage: " de , en ")
+
+        #expect(language == "de")
+    }
+
+    @Test
+    func `falls back to the default for an unsupported language`() {
+        let language = negotiate(acceptLanguage: "fr")
+
+        #expect(language == "en")
+    }
+
+    @Test
+    func `falls back to the default for a missing header`() {
+        let language = negotiate(acceptLanguage: nil)
+
+        #expect(language == "en")
+    }
+
+    @Test
+    func `falls back to the default for an empty header`() {
+        let language = negotiate(acceptLanguage: "")
+
+        #expect(language == "en")
+    }
+
+    @Test
+    func `falls back to the default for a header without language tags`() {
+        let language = negotiate(acceptLanguage: " , ;q=0.5,")
+
+        #expect(language == "en")
+    }
+
+}