feat: translation middleware

internal/components/translate/middleware.go

@@ -0,0 +1,85 @@
+package translate
+
+import (
+	"context"
+	"net/http"
+	"strings"
+)
+
+func (s *Service) Middleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		path := r.URL.Path
+		segments := []string{}
+		for segment := range strings.SplitSeq(path, "/") {
+			if segment != "" {
+				segments = append(segments, segment)
+			}
+		}
+
+		// 1. Check if the first segment is a supported language.
+		var currentLang string
+		if len(segments) >= 1 {
+			potentialLang := segments[0]
+			if _, ok := s.translations[potentialLang]; ok {
+				currentLang = potentialLang
+			}
+		}
+
+		if currentLang != "" {
+			// CASE A: Language is present in the URL.
+			// Remove the language from the path so the router sees the clean path.
+			newPath := "/" + strings.Join(segments[1:], "/")
+			if newPath == "" {
+				newPath = "/"
+			}
+
+			// Update the request URL path.
+			r.URL.Path = newPath
+
+			// Inject translator into context.
+			ctx := context.WithValue(r.Context(), serviceKey, s)
+			ctx = context.WithValue(ctx, langKey, currentLang)
+
+			// Pass control to the next handler with the modified request.
+			next.ServeHTTP(w, r.WithContext(ctx))
+			return
+		}
+
+		// CASE B: Language is NOT in the URL.
+		// Detect best language from Accept-Language header.
+		detectedLang := s.detectLanguage(r.Header.Get("Accept-Language"))
+
+		// Redirect to the URL with the language prefix.
+		targetURL := "/" + detectedLang + path
+		if r.URL.RawQuery != "" {
+			targetURL += "?" + r.URL.RawQuery
+		}
+
+		http.Redirect(w, r, targetURL, http.StatusFound)
+	})
+}
+
+// detectLanguage parses the Accept-Language header and returns the best matching supported language.
+func (s *Service) detectLanguage(header string) string {
+	if header == "" {
+		return s.defaultLanguage
+	}
+
+	// Simple parser for Accept-Language: en-US,en;q=0.9,de;q=0.8
+	// We only care about the first match for simplicity here, or we could rank them.
+	parts := strings.Split(header, ",")
+	for _, part := range parts {
+		tag := strings.Split(strings.TrimSpace(part), ";")[0]
+		// Check for exact match (e.g., "en-US")
+		if _, ok := s.translations[tag]; ok {
+			return tag
+		}
+		// Check for base match (e.g., "en" from "en-US")
+		base := strings.Split(tag, "-")[0]
+		if _, ok := s.translations[base]; ok {
+			return base
+		}
+	}
+
+	return s.defaultLanguage
+}