btrc-hub/frontend/src/lib/locales.ts

import { apiGet } from '@/lib/api'
import { currentRenderContext } from '@/lib/renderContext'

import type { To } from 'react-router-dom'

export const SUPPORTED_LOCALES = ['ja', 'ain-Kana'] as const

export type LocaleCode = typeof SUPPORTED_LOCALES[number]

export type AvailableLocale = { code: string; name: string }


export const fetchLocales = (): Promise<{ locales: AvailableLocale[] }> =>
    apiGet ('/locales')


export const isLocaleCode = (value: unknown): value is LocaleCode =>
    SUPPORTED_LOCALES.some (locale => locale === value)


export const localeLanguage = (locale: LocaleCode): 'ja' | 'ain' =>
    locale === 'ja' ? 'ja' : 'ain'


export const localeFromPath = (pathname: string): LocaleCode | null => {
  const segment = pathname.split (/[/?#]/)[1]
  return isLocaleCode (segment) ? segment : null
}


export const resolveViewingLocale = (
    pathname: string,
    routeLocale?: unknown,
): LocaleCode =>
    isLocaleCode (routeLocale) ? routeLocale : localeFromPath (pathname) ?? 'ja'


export const currentViewingLocale = (): LocaleCode =>
    resolveViewingLocale (currentRenderContext ()?.pathname ?? '')


export const unlocalisedPath = (pathname: string): string => {
  const locale = localeFromPath (pathname)
  return locale == null ? pathname : pathname.slice (locale.length + 1) || '/'
}


export const localiseTo = (to: To, locale: LocaleCode): To => {
  const pathname = typeof to === 'string' ? to : to.pathname
  if (pathname == null
      || !(pathname.startsWith ('/'))
      || pathname.startsWith ('//')
      || localeFromPath (pathname) != null)
    return to

  const localised = `/${ locale }${ pathname }`
  return typeof to === 'string' ? localised : { ...to, pathname: localised }
}


export const switchLocalePath = (
    location: { pathname: string; search: string; hash: string },
    locale: LocaleCode,
): string =>
    `/${ locale }${ unlocalisedPath (location.pathname) }${ location.search }${ location.hash }`


// Keep automatic selection independent of the page and API route trees.
export const automaticallySelectedLocale = (): LocaleCode => 'ja'


export const legacyLocalePath = (
    location: { pathname: string; search: string; hash: string },
    isPage: (pathname: string) => boolean = () => false,
): string | null => {
  if (localeFromPath (location.pathname) != null || !isPage (location.pathname))
    return null
  return switchLocalePath (location, automaticallySelectedLocale ())
}