/**
 * Runtime configuration, written by the server as `config.js` when it places a
 * build — never baked in.
 *
 * One build is promoted between environments unchanged, so an API URL compiled
 * at build time would be the *source* environment's URL everywhere it lands.
 *
 * SAME_ORIGIN exists because an empty string is falsy and could never survive
 * the `||` chain, which is exactly what "use the current origin" has to do.
 */
export function resolveConfigValue(key, fallback = '') {
  const runtime = (window.__RUNTIME_CONFIG__ || {})[key]
  // Gated on DEV: a production build with no config.js must fail loudly rather
  // than quietly calling whichever backend happened to build it.
  const devFallback = import.meta.env.DEV ? (import.meta.env[key] ?? '') : ''
  const value = runtime || devFallback || fallback
  return value === 'SAME_ORIGIN' ? window.location.origin.replace(/\/$/, '') : value
}

export function requireConfigValue(key) {
  const value = resolveConfigValue(key)
  if (!value) {
    throw new Error(
      `Missing runtime config "${key}". The server writes config.js when it ` +
        `places the build; for local dev set ${key} in .env.`,
    )
  }
  return value
}

/**
 * The mount path this app is served under, read from the `<base href>` the
 * server writes into index.html. Drives the router basename, so one build
 * serves any mount path without a rebuild.
 *
 * `import.meta.env.BASE_URL` is NOT usable here — with Vite's relative base it
 * resolves to "./".
 *
 * It reads the TAG, not `document.baseURI`. With no <base> in the document —
 * which is every `npm run dev` session, where the placeholder is still an HTML
 * comment — baseURI falls back to the current page URL, so the basename became
 * whatever deep path happened to be loaded. Open /lead/16911 directly and every
 * link then rendered under it: /lead/16911/lead/11411, and again on the next
 * click. Unmounted means mounted at the root.
 */
export function basePath() {
  const tag = document.querySelector('base[href]')
  if (!tag) return '/'
  const path = new URL(tag.href, window.location.origin).pathname
  // A relative href ("./") resolves against the current URL and would reintroduce
  // exactly the same drift. Only an absolute mount path is a mount path.
  return tag.getAttribute('href').startsWith('/') ? path : '/'
}