import { headers, cookies } from "next/headers";
import { auth } from "@/lib/auth/server";
import type { Locale } from "@/lib/i18n/provider";
import { MARKETING_LOCALE_COOKIE } from "@/lib/marketing-locale-cookie";

export { MARKETING_LOCALE_COOKIE };

/**
 * Locale for the public marketing pages — cookie-based, not tied to a user
 * account (visitors there have no session). Separate from the authenticated
 * app's locale system (`lib/i18n/provider.tsx`'s `useLocale`/`setLocale`),
 * which persists to `users.locale` via an authenticated PATCH that would
 * just 401 for an anonymous visitor and revert the UI.
 */
/** Parses an `Accept-Language` header and returns the first supported
 * locale it lists, in the browser's stated preference order — ignoring
 * unsupported languages (e.g. "de", "es") rather than stopping at them. */
function localeFromAcceptLanguage(header: string | null): Locale | null {
  if (!header) return null;
  const tags = header
    .split(",")
    .map((part) => part.split(";")[0]!.trim().toLowerCase())
    .filter(Boolean);
  for (const tag of tags) {
    if (tag.startsWith("fr")) return "fr";
    if (tag.startsWith("en")) return "en";
  }
  return null;
}

export async function getMarketingLocale(): Promise<Locale> {
  const store = await cookies();
  const cookieValue = store.get(MARKETING_LOCALE_COOKIE)?.value;
  if (cookieValue === "fr" || cookieValue === "en") return cookieValue;

  // No explicit choice saved yet (first visit, or cookies cleared) — honor
  // the visitor's browser language instead of always defaulting to English.
  const headerStore = await headers();
  return localeFromAcceptLanguage(headerStore.get("accept-language")) ?? "en";
}

/** A logged-in visitor's own saved locale wins (matches what they see
 * everywhere else in the app); otherwise the marketing cookie. */
export async function getEffectiveMarketingLocale(): Promise<Locale> {
  const session = await auth.api.getSession({ headers: await headers() }).catch(() => null);
  const sessionLocale = (session?.user as { locale?: string } | undefined)?.locale;
  if (sessionLocale === "en" || sessionLocale === "fr") return sessionLocale;
  return getMarketingLocale();
}