AstralRinth/apps/frontend/src/plugins/i18n.ts

import { moderationLocaleModules } from '@modrinth/moderation'
import {
	type CrowdinMessages,
	I18N_INJECTION_KEY,
	type I18nContext,
	LOCALES,
	transformCrowdinMessages,
	uiLocaleModules,
	useDebugLogger,
} from '@modrinth/ui'
import IntlMessageFormat from 'intl-messageformat'
import { LRUCache } from 'lru-cache'

const debug = useDebugLogger('i18n')
const DEFAULT_LOCALE = 'en-US'

const frontendLocaleModules = import.meta.glob<{ default: CrowdinMessages }>(
	'../locales/*/index.json',
	{ eager: false },
)

const messageCache = new LRUCache<string, Record<string, string>>({ max: 10 })
const formatterCache = new LRUCache<string, IntlMessageFormat>({ max: 1000 })
const loadingPromises = new Map<string, Promise<void>>() // Dedupe concurrent loads

type LocaleModules = Record<string, () => Promise<{ default: CrowdinMessages }>>

// Find the loader for a locale code in a glob result (paths end with /{code}/index.json)
function findLocaleLoader(modules: LocaleModules, code: string) {
	for (const [path, loader] of Object.entries(modules)) {
		if (path.endsWith(`/${code}/index.json`)) {
			return loader
		}
	}
	return undefined
}

async function loadLocale(code: string): Promise<void> {
	if (messageCache.has(code)) {
		debug('loadLocale: already cached', code)
		return
	}

	// Dedupe concurrent requests for the same locale
	const existing = loadingPromises.get(code)
	if (existing) {
		debug('loadLocale: already loading', code)
		return existing
	}

	debug('loadLocale: starting', code)

	const promise = (async () => {
		const frontendLoader = findLocaleLoader(frontendLocaleModules, code)
		const uiLoader = findLocaleLoader(uiLocaleModules, code)
		const moderationLoader = findLocaleLoader(moderationLocaleModules, code)

		debug('loadLocale: loaders found', {
			code,
			frontend: !!frontendLoader,
			ui: !!uiLoader,
			moderation: !!moderationLoader,
		})

		// Load all sources in parallel
		const [uiData, moderationData, frontendData] = await Promise.all([
			uiLoader?.().catch((e) => {
				debug('loadLocale: ui loader failed', code, e)
				return null
			}),
			moderationLoader?.().catch((e) => {
				debug('loadLocale: moderation loader failed', code, e)
				return null
			}),
			frontendLoader?.().catch((e) => {
				debug('loadLocale: frontend loader failed', code, e)
				return null
			}),
		])

		debug('loadLocale: data loaded', {
			code,
			uiKeys: uiData ? Object.keys(uiData.default).length : 0,
			moderationKeys: moderationData ? Object.keys(moderationData.default).length : 0,
			frontendKeys: frontendData ? Object.keys(frontendData.default).length : 0,
		})

		// Merge: UI (base) → moderation → frontend (highest priority)
		const mergedMessages: Record<string, string> = {}
		if (uiData) Object.assign(mergedMessages, transformCrowdinMessages(uiData.default))
		if (moderationData)
			Object.assign(mergedMessages, transformCrowdinMessages(moderationData.default))
		if (frontendData) Object.assign(mergedMessages, transformCrowdinMessages(frontendData.default))

		debug('loadLocale: merged', code, 'total keys:', Object.keys(mergedMessages).length)

		if (Object.keys(mergedMessages).length > 0) {
			messageCache.set(code, mergedMessages)
		}
	})()

	loadingPromises.set(code, promise)
	try {
		await promise
	} finally {
		loadingPromises.delete(code)
	}
}

function parseAcceptLanguage(header: string): string | null {
	try {
		for (const lang of header
			.split(',')
			.map((l) => l.split(';')[0]?.trim())
			.filter(Boolean)) {
			const exact = LOCALES.find((loc) => loc.code === lang)
			if (exact) return exact.code
			const prefix = LOCALES.find((loc) => loc.code.startsWith(lang.split('-')[0] + '-'))
			if (prefix) return prefix.code
		}
	} catch {
		// Malformed header, ignore
	}
	return null
}

export default defineNuxtPlugin({
	name: 'i18n',
	enforce: 'pre',
	async setup(nuxtApp) {
		const locale = useState<string>('i18n-locale', () => DEFAULT_LOCALE)

		function t(key: string, values?: Record<string, unknown>): string {
			const currentLocale = locale.value
			const localeMessages = messageCache.get(currentLocale)
			const fallbackMessages = messageCache.get(DEFAULT_LOCALE)
			const msg = localeMessages?.[key] ?? fallbackMessages?.[key]

			if (!msg) {
				debug('t: key not found', {
					key,
					locale: currentLocale,
					hasLocaleMessages: !!localeMessages,
					hasFallbackMessages: !!fallbackMessages,
				})
				return key
			}

			if (!values || Object.keys(values).length === 0) return msg

			const cacheKey = `${currentLocale}:${msg}`
			let formatter = formatterCache.get(cacheKey)
			if (!formatter) {
				formatter = new IntlMessageFormat(msg, currentLocale)
				formatterCache.set(cacheKey, formatter)
			}
			try {
				const result = formatter.format(values) as string
				if (import.meta.dev && typeof result !== 'string') {
					debug('t: format returned non-string', key, typeof result)
				}
				return result
			} catch {
				return msg
			}
		}

		async function setLocale(newLocale: string): Promise<void> {
			debug('setLocale: called', { newLocale, currentLocale: locale.value })

			if (!LOCALES.some((l) => l.code === newLocale)) {
				debug('setLocale: invalid locale', newLocale)
				return
			}

			await loadLocale(newLocale)

			debug('setLocale: loaded', {
				newLocale,
				cacheHas: messageCache.has(newLocale),
				cacheKeys: messageCache.get(newLocale)
					? Object.keys(messageCache.get(newLocale)!).length
					: 0,
			})

			locale.value = newLocale
			useCookie('locale', { maxAge: 31536000, path: '/' }).value = newLocale
		}

		// Detect initial locale (cookie > Accept-Language > default)
		const cookieLocale = useCookie('locale').value
		let detectedLocale = DEFAULT_LOCALE
		if (cookieLocale && LOCALES.some((l) => l.code === cookieLocale)) {
			detectedLocale = cookieLocale
			debug('init: locale from cookie', detectedLocale)
		} else if (import.meta.server) {
			const acceptLang = useRequestHeaders(['accept-language'])['accept-language']
			if (acceptLang) {
				detectedLocale = parseAcceptLanguage(acceptLang) ?? DEFAULT_LOCALE
				debug('init: locale from Accept-Language', detectedLocale)
			}
		}

		debug('init: detected locale', { detectedLocale, cookieLocale, isServer: import.meta.server })

		// Load locales (hits cache after first request)
		await loadLocale(DEFAULT_LOCALE)
		if (detectedLocale !== DEFAULT_LOCALE) await loadLocale(detectedLocale)
		locale.value = detectedLocale

		debug('init: complete', { locale: locale.value })

		const context: I18nContext = { locale, t, setLocale }
		nuxtApp.vueApp.provide(I18N_INJECTION_KEY, context)
	},
})