Function detectDomainLocale

packages/next-routing/src/i18n.ts:22–48

(
  domains: I18nDomain[] | undefined,
  hostname: string | undefined,
  detectedLocale?: string
)

 * Detects the domain locale based on hostname or detected locale
 */
export function detectDomainLocale(
  domains: I18nDomain[] | undefined,
  hostname: string | undefined,
  detectedLocale?: string
): I18nDomain | undefined {
  if (!domains) return undefined

  const normalizedHostname = hostname?.toLowerCase()
  const normalizedLocale = detectedLocale?.toLowerCase()

  for (const domain of domains) {
    // Remove port if present
    const domainHostname = domain.domain.split(':', 1)[0].toLowerCase()

    if (
      normalizedHostname === domainHostname ||
      normalizedLocale === domain.defaultLocale.toLowerCase() ||
      domain.locales?.some(
        (locale) => locale.toLowerCase() === normalizedLocale
      )
    ) {
      return domain
    }
  }

  return undefined
}

/**
 * Normalizes a pathname by removing the locale prefix if present