tibi-svelte-starter/frontend/src/lib/i18n.ts

import { writable, derived, get } from "svelte/store"
import { location } from "./store"

/**
 * Supported languages configuration.
 * Add more languages as needed for your project.
 */
export const SUPPORTED_LANGUAGES = ["de", "en"] as const
export type SupportedLanguage = (typeof SUPPORTED_LANGUAGES)[number]

export const DEFAULT_LANGUAGE: SupportedLanguage = "de"

export const LANGUAGE_LABELS: Record<SupportedLanguage, string> = {
    de: "Deutsch",
    en: "English",
}

/**
 * Route translations for localized URLs.
 * Add entries for routes that need translated slugs.
 * Example: { about: { de: "ueber-uns", en: "about" } }
 */
export const ROUTE_TRANSLATIONS: Record<string, Record<SupportedLanguage, string>> = {
    // Add your route translations here:
    // about: { de: "ueber-uns", en: "about" },
}

export const getLocalizedRoute = (canonicalRoute: string, lang: SupportedLanguage): string => {
    const translations = ROUTE_TRANSLATIONS[canonicalRoute]
    if (translations && translations[lang]) {
        return translations[lang]
    }
    return canonicalRoute
}

export const getCanonicalRoute = (localizedSegment: string): string => {
    for (const [canonical, translations] of Object.entries(ROUTE_TRANSLATIONS)) {
        for (const translated of Object.values(translations)) {
            if (translated === localizedSegment) {
                return canonical
            }
        }
    }
    return localizedSegment
}

/**
 * Extract the language code from a URL path.
 * Returns null if no valid language prefix is found.
 */
export const extractLanguageFromPath = (path: string): SupportedLanguage | null => {
    const match = path.match(/^\/([a-z]{2})(\/|$)/)
    if (match && SUPPORTED_LANGUAGES.includes(match[1] as SupportedLanguage)) {
        return match[1] as SupportedLanguage
    }
    return null
}

export const stripLanguageFromPath = (path: string): string => {
    const lang = extractLanguageFromPath(path)
    if (lang) {
        const stripped = path.slice(3)
        return stripped || "/"
    }
    return path
}

export const getRoutePath = (fullPath: string): string => {
    const stripped = stripLanguageFromPath(fullPath)
    if (stripped === "/" || stripped === "") {
        return "/"
    }
    const segments = stripped.split("/").filter(Boolean)
    if (segments.length > 0) {
        const canonicalFirst = getCanonicalRoute(segments[0])
        if (canonicalFirst !== segments[0]) {
            segments[0] = canonicalFirst
            return "/" + segments.join("/")
        }
    }
    return stripped
}

/**
 * Derived store: current language based on URL.
 */
export const currentLanguage = derived(location, ($location) => {
    const path = $location.path || "/"
    return extractLanguageFromPath(path) || DEFAULT_LANGUAGE
})

/**
 * Writable store for the selected language.
 */
export const selectedLanguage = writable<SupportedLanguage>(DEFAULT_LANGUAGE)

if (typeof window !== "undefined") {
    const initialLang = extractLanguageFromPath(window.location.pathname)
    if (initialLang) {
        selectedLanguage.set(initialLang)
    }
}

if (typeof window !== "undefined") {
    location.subscribe(($loc) => {
        const lang = extractLanguageFromPath($loc.path)
        if (lang) {
            selectedLanguage.set(lang)
        }
    })
}

/**
 * Get the localized path for a given route and language.
 */
export const localizedPath = (path: string, lang?: SupportedLanguage): string => {
    const language = lang || get(currentLanguage)
    if (path === "/" || path === "") {
        return `/${language}`
    }
    let cleanPath = stripLanguageFromPath(path)
    cleanPath = cleanPath.startsWith("/") ? cleanPath : `/${cleanPath}`
    const segments = cleanPath.split("/").filter(Boolean)
    if (segments.length > 0) {
        const canonicalFirst = getCanonicalRoute(segments[0])
        const localizedFirst = getLocalizedRoute(canonicalFirst, language)
        segments[0] = localizedFirst
    }
    const translatedPath = "/" + segments.join("/")
    return `/${language}${translatedPath}`
}

/**
 * Derived store for localized href.
 */
export const localizedHref = (path: string) => {
    return derived(currentLanguage, ($lang) => localizedPath(path, $lang))
}

export const isValidLanguage = (lang: string): lang is SupportedLanguage => {
    return SUPPORTED_LANGUAGES.includes(lang as SupportedLanguage)
}

/**
 * Get the browser's preferred language, falling back to default.
 */
export const getBrowserLanguage = (): SupportedLanguage => {
    if (typeof navigator === "undefined") {
        return DEFAULT_LANGUAGE
    }
    const browserLangs = navigator.languages || [navigator.language]
    for (const lang of browserLangs) {
        const code = lang.split("-")[0].toLowerCase()
        if (isValidLanguage(code)) {
            return code
        }
    }
    return DEFAULT_LANGUAGE
}

/**
 * Get URL for switching to a different language.
 */
export const getLanguageSwitchUrl = (newLang: SupportedLanguage): string => {
    const currentPath = typeof window !== "undefined" ? window.location.pathname : "/"
    const canonicalPath = getRoutePath(currentPath)
    return localizedPath(canonicalPath, newLang)
}