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