/* ============================================================================
   I18N HOOKS
   ----------------------------------------------------------------------------
   The locale is a property of the URL, never of a cookie or of client state,
   so every hook here is derived from the router - which means SSR and the
   first client render agree by construction and hydration never mismatches.

   `useParams().lang` is the fast path inside a page route. The root layout and
   the root ErrorBoundary sit ABOVE the ":lang" segment, where that param does
   not exist, so the pathname is the fallback and both are correct.
   ========================================================================= */

import { useMemo } from "react";
import { useLocation, useMatches, useParams } from "react-router";

import {
  DEFAULT_LOCALE,
  dirFor,
  getLocaleFromPathname,
  isLocale,
  type Direction,
  type Locale,
} from "./config";
import { alternatePath, localizedPath, sectionPath } from "./paths";
import type { RouteSlugKey } from "./paths";
import {
  createTranslator,
  getMessages,
  type Messages,
  type Translator,
} from "./t";

/** The locale of the page being rendered. */
export function useLocale(): Locale {
  const params = useParams();
  const { pathname } = useLocation();
  const lang = params.lang;

  return useMemo(() => {
    if (isLocale(lang)) return lang;
    return getLocaleFromPathname(pathname) ?? DEFAULT_LOCALE;
  }, [lang, pathname]);
}

/** "ltr" for /en/*, "rtl" for /ar/*. Mirrors `<html dir>`. */
export function useDirection(): Direction {
  return dirFor(useLocale());
}

export interface Translation {
  readonly locale: Locale;
  readonly dir: Direction;
  /** `t("nav.sections.about")`, `t("pagination.page", { page, pageCount })`. */
  readonly t: Translator;
  /** The raw catalogue, for the rare case a whole namespace is needed. */
  readonly messages: Messages;
  /** `/{locale}` prefixed URL for an unprefixed path. */
  readonly localizedPath: (path: string) => string;
  /** The locale-prefixed URL of one of the ten sections. */
  readonly sectionPath: (key: RouteSlugKey) => string;
}

/** Everything a component needs to render in the current language. */
export function useTranslation(): Translation {
  const locale = useLocale();

  return useMemo(
    () => ({
      locale,
      dir: dirFor(locale),
      t: createTranslator(locale),
      messages: getMessages(locale),
      localizedPath: (path: string) => localizedPath(path, locale),
      sectionPath: (key: RouteSlugKey) => sectionPath(key, locale),
    }),
    [locale],
  );
}

/**
 * The counterpart-language URL for the current location, query string and
 * fragment preserved. This is what the header's language switch points at.
 */
export function useAlternatePath(targetLocale: Locale): string {
  const { pathname, search, hash } = useLocation();

  return useMemo(
    () => alternatePath(pathname, targetLocale, { search, hash }),
    [pathname, search, hash, targetLocale],
  );
}

/**
 * Read a value off the deepest route `handle` that declares it. Used by the
 * shell to let a page opt into a light navigation or footer surface.
 */
export function useRouteHandleValue<T>(
  read: (handle: Record<string, unknown>) => T | undefined,
): T | undefined {
  const matches = useMatches();

  for (let index = matches.length - 1; index >= 0; index -= 1) {
    const handle = matches[index]?.handle;
    if (handle && typeof handle === "object") {
      const value = read(handle as Record<string, unknown>);
      if (value !== undefined) return value;
    }
  }

  return undefined;
}