const OBJECT_NOTATION_MATCHER = /\[(.*?)\]|(\w+)/g;

export function get<T>(
  obj: {[key: string]: any} | undefined,
  keypath: string | string[],
  defaultValue?: T,
): T | any {
  if (obj == null) return undefined;

  const keys = Array.isArray(keypath) ? keypath : getKeypath(keypath);
  let acc = obj;
  // eslint-disable-next-line @typescript-eslint/prefer-for-of
  for (let i = 0; i < keys.length; i++) {
    const val = acc[keys[i]];
    if (val === undefined) return defaultValue;
    acc = val;
  }

  return acc;
}

function getKeypath(str: string) {
  const path = [];
  let result: RegExpExecArray | null;
  while ((result = OBJECT_NOTATION_MATCHER.exec(str))) {
    const [, first, second] = result;
    path.push(first || second);
  }

  return path;
}