package httpapi

import (
	"net/http"
	"strings"

	"github.com/descrybe/descrybe-v2/apps/api/internal/i18n"
)

// localeResponseWriter carries the resolved UI/API locale for Error()/CodedError.
type localeResponseWriter struct {
	http.ResponseWriter
	locale string
}

func (w *localeResponseWriter) Locale() string { return w.locale }

func (w *localeResponseWriter) Unwrap() http.ResponseWriter { return w.ResponseWriter }

type localeCarrier interface {
	Locale() string
}

type responseUnwrapper interface {
	Unwrap() http.ResponseWriter
}

func localeOf(w http.ResponseWriter) string {
	for w != nil {
		if lc, ok := w.(localeCarrier); ok {
			return lc.Locale()
		}
		uw, ok := w.(responseUnwrapper)
		if !ok {
			break
		}
		w = uw.Unwrap()
	}
	return i18n.Default
}

// Locale resolves Accept-Language into a supported UI locale, stores it on the
// request context and ResponseWriter, and sets Vary: Accept-Language.
func Locale(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		lang := i18n.Resolve(r.Header.Get("Accept-Language"))
		ctx := i18n.WithLocale(r.Context(), lang)
		if v := w.Header().Get("Vary"); v == "" {
			w.Header().Set("Vary", "Accept-Language")
		} else if !containsCSVToken(v, "Accept-Language") {
			w.Header().Set("Vary", v+", Accept-Language")
		}
		next.ServeHTTP(&localeResponseWriter{ResponseWriter: w, locale: lang}, r.WithContext(ctx))
	})
}

func containsCSVToken(header, token string) bool {
	for _, part := range strings.Split(header, ",") {
		if strings.TrimSpace(part) == token {
			return true
		}
	}
	return false
}