PronounsPage/server/middleware/macrolanguage-redirect.ts

import { sendRedirect } from 'h3';

import type { LazyDatabase } from '..';

import locales from '~~/locale/locales.ts';
import type { LocaleDescription } from '~~/locale/locales.ts';
import { getLocale, loadConfig } from '~~/server/data.ts';

/**
 * When the current locale represents a macrolanguage, redirects the user to the
 * appropriate sublanguage based on the Accept-Language header.
 */
export default defineEventHandler(async (event) => {
    const { node: { req }, path } = event;

    const locale = getLocale(event);
    const config = await loadConfig(locale);

    if (
        !config.macrolanguage?.enabled ||
        /(?:langswitch|__nuxt_error)(?:\/|#|\?|$)/.test(path) ||
        path.startsWith('/api/')
    ) {
        return;
    }

    const langswitchPath = path !== '/'
        ? `/langswitch?return=${encodeURIComponent(path)}`
        : '/langswitch';
    const acceptLanguage = req.headers['accept-language'];

    // Map individual languages to their locales
    const individualLanguages = config.macrolanguage?.languages || [];
    const subLocales = new Map<string, LocaleDescription>(
        // @ts-expect-error I don't have a clue why this is bugging out
        individualLanguages
            .map((subLanguage) => {
                const foundLocale = locales.find(
                    (locale) => locale.code === subLanguage.code,
                )!;
                return foundLocale ? [subLanguage.code, foundLocale] : null;
            })
            .filter(
                // @ts-expect-error TypeScript is confused about the type here
                (locale): locale is [string, LocaleDescription][] => locale !== null,
            ),
    );

    // Only redirect to individual locale automatically if all individual languages
    // have some language codes to match against the Accept-Language header
    const canAutoRedirect = individualLanguages.every(
        (subLanguage) => subLanguage.matches?.some(Boolean),
    );

    if (!acceptLanguage || !individualLanguages || !canAutoRedirect) {
        return sendRedirect(event, langswitchPath);
    }

    // Get language codes from the Accept-Language header, ordered by quality
    const requestedLangs = acceptLanguage.split(',').map((language) => {
        const [lang, quality] = language.split(';q=');
        return { lang, quality: quality ? Number.parseFloat(quality) : 1 };
    })
        .sort((a, b) => b.quality - a.quality)
        .map((acceptEntry) => acceptEntry.lang);

    // If the requested route is for a user profile, get which individual
    // languages the user has a profile for
    if (path.startsWith('/@') && event.context.db) {
        const db = event.context.db as LazyDatabase;
        const username = /^\/@([^/?#]+)/.exec(path)?.[1];

        if (!username) {
            return sendRedirect(event, langswitchPath);
        }

        const profiles =
            (await db.all<{ id: string; locale: string; username: string }>(`
                SELECT profiles.id, profiles.locale, users.username
                FROM profiles
                LEFT JOIN users on profiles.userId = users.id
                WHERE users.username = ?
                AND profiles.locale IN (${
                individualLanguages.map(() => '?').join(', ')
                })
            `, [username, ...individualLanguages.map((lang) => lang.code)]));

        if (profiles.length !== 1) {
            return sendRedirect(event, langswitchPath);
        }

        const foundLocale = subLocales.get(profiles[0].locale);

        if (foundLocale) {
            return sendRedirect(event, `${foundLocale.url}${req.url}`);
        }

        return sendRedirect(event, langswitchPath);
    }

    // Find the first locale matching an individual language of the
    // macrolanguage
    let localeDescription: LocaleDescription | undefined;

    // Iterate in order of the Accept-Language header's quality values, to
    // prioritize the user's preferred languages
    for (const tag of requestedLangs) {
        const languageConfig = individualLanguages.find(
            (lang) => lang.matches?.includes(tag),
        );

        if (!languageConfig) {
            break;
        }

        const foundLocaleDescription = subLocales.get(languageConfig.code);

        if (foundLocaleDescription) {
            localeDescription = foundLocaleDescription;
            break;
        }
    }

    if (!localeDescription) {
        return sendRedirect(event, langswitchPath);
    }

    return sendRedirect(event, `${localeDescription.url}${req.url}`);
});