src/hooks.server.ts


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import { detectLocale, i18n, isLocale } from '$i18n/i18n-util'
import { loadAllLocales } from '$i18n/i18n-util.sync'
import type { Handle, RequestEvent } from '@sveltejs/kit'
import { initAcceptLanguageHeaderDetector } from 'typesafe-i18n/detectors'

loadAllLocales()
const L = i18n()

export const handle: Handle = async ({ event, resolve }) => {
    // read language slug
    const [, lang] = event.url.pathname.split('/')

    // redirect to base locale if no locale slug was found
    if (!lang) {
        const locale = getPreferredLocale(event)

        return new Response(null, {
            status: 302,
            headers: { Location: `/${locale}` },
        })
    }

    // if slug is not a locale, use base locale (e.g. api endpoints)
    const locale = isLocale(lang) ? (lang as Locales) : getPreferredLocale(event)
    const LL = L[locale]

    // bind locale and translation functions to current request
    event.locals.locale = locale
    event.locals.LL = LL

    console.info(LL.log({ fileName: 'hooks.server.ts' }))

    // replace html lang attribute with correct language
    return resolve(event, { transformPageChunk: ({ html }) => html.replace('%lang%', locale) })
}

const getPreferredLocale = ({ request }: RequestEvent) => {
    // detect the preferred language the user has configured in his browser
    // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Language
    const acceptLanguageDetector = initAcceptLanguageHeaderDetector(request)

    return detectLocale(acceptLanguageDetector)
}