function isPlainObject(value) {
  if (value === null || typeof value !== "object") {
    return false;
  }
  const prototype = Object.getPrototypeOf(value);
  if (prototype !== null && prototype !== Object.prototype && Object.getPrototypeOf(prototype) !== null) {
    return false;
  }
  if (Symbol.iterator in value) {
    return false;
  }
  if (Symbol.toStringTag in value) {
    return Object.prototype.toString.call(value) === "[object Module]";
  }
  return true;
}

function _defu(baseObject, defaults, namespace = ".", merger) {
  if (!isPlainObject(defaults)) {
    return _defu(baseObject, {}, namespace, merger);
  }
  const object = Object.assign({}, defaults);
  for (const key in baseObject) {
    if (key === "__proto__" || key === "constructor") {
      continue;
    }
    const value = baseObject[key];
    if (value === null || value === void 0) {
      continue;
    }
    if (merger && merger(object, key, value, namespace)) {
      continue;
    }
    if (Array.isArray(value) && Array.isArray(object[key])) {
      object[key] = [...value, ...object[key]];
    } else if (isPlainObject(value) && isPlainObject(object[key])) {
      object[key] = _defu(
        value,
        object[key],
        (namespace ? `${namespace}.` : "") + key.toString(),
        merger
      );
    } else {
      object[key] = value;
    }
  }
  return object;
}
function createDefu(merger) {
  return (...arguments_) => (
    // eslint-disable-next-line unicorn/no-array-reduce
    arguments_.reduce((p, c) => _defu(p, c, "", merger), {})
  );
}
const defu = createDefu();
const defuFn = createDefu((object, key, currentValue) => {
  if (object[key] !== void 0 && typeof currentValue === "function") {
    object[key] = currentValue(object[key]);
    return true;
  }
});
const defuArrayFn = createDefu((object, key, currentValue) => {
  if (Array.isArray(object[key]) && typeof currentValue === "function") {
    object[key] = currentValue(object[key]);
    return true;
  }
});

export { createDefu, defu as default, defu, defuArrayFn, defuFn };