type TranslationDict = { [key: string]: string | TranslationDict };

/**
 * Recursively merge `extra` into `base`, so a partial fragment ADDS keys into
 * existing namespaces instead of replacing them. A shallow spread would clobber a
 * whole namespace (e.g. `...drift` last would drop every other `socialUi` key).
 * Plain nested string dictionaries only.
 */
export function deepMerge<T extends TranslationDict>(base: T, extra: TranslationDict): T {
  const out: TranslationDict = { ...base };
  for (const [key, value] of Object.entries(extra)) {
    const current = out[key];
    if (
      value && typeof value === 'object' && !Array.isArray(value) &&
      current && typeof current === 'object' && !Array.isArray(current)
    ) {
      out[key] = deepMerge(current as TranslationDict, value as TranslationDict);
    } else {
      out[key] = value;
    }
  }
  return out as T;
}