type Messages = Record<string, Record<string, string>>

export function createI18n({ defaultLocale, messages }: { defaultLocale: string; messages: Messages }) {
  function format(template: string, params?: Record<string, string | number>) {
    if (!params) return template
    return template.replace(/\{(\w+)\}/g, (_, k) => (params[k] !== undefined ? String(params[k]) : `{${k}}`))
  }

  function getMessage(locale: string, key: string): string | undefined {
    const m = messages[locale] || {}
    if (m[key] !== undefined) return m[key]
    const base = messages[defaultLocale] || {}
    return base[key]
  }

  function t(locale: string, key: string, params?: Record<string, string | number>): string {
    const msg = getMessage(locale, key)
    if (typeof msg === 'string') return format(msg, params)
    return key
  }

  return { t }
}