a simple querystring parser with nesting support

parse.swift

func parse(qs: String) -> [String: Any]? {

    guard let regex = try? NSRegularExpression.init(
        pattern: "(?:[^\\[\\]]+)",
        options: NSRegularExpression.Options(rawValue: 0)
    ) else {
        return nil
    }

    return qs
        .split(separator: "&")
        .map { $0.split(separator: "=") }
        .reduce(NSMutableDictionary()) { (accu, curr) in

            // []에 대한 처리를 쉽게 하기 위해서 querystring 구성 시 separator로 사용한 &를 넣어준다.
            // (keyPath 추적시 &가 나오면 Array로 판단하기 위함)
            let key = String(String(curr[0]).replacingOccurrences(of: "[]", with: "[&]"))
            let val = curr.count > 1 ? curr[1]: ""

            let matches = regex.matches(
                in: key,
                options: NSRegularExpression.MatchingOptions(rawValue: 0),
                range: NSRange.init(location: 0, length: key.count)
            )

            let keyPath = matches.map { (checkResult, _) -> String in
                let idxStart = String.Index(encodedOffset: checkResult.range.location)
                let idxEnd   = String.Index(encodedOffset: checkResult.range.location + checkResult.range.length)
                return String(key[idxStart..<idxEnd])
            }

            var storage: Any = accu

            let count = keyPath.count
            for i in 0..<count {

                let cKey = keyPath[i]

                // 다음 path가 있으므로 더 들어가야 함.
                if let nKey = i < count - 1 ? keyPath[i+1] : nil {

                    switch storage {
                    case let _storage as NSMutableDictionary:
                        switch (nKey, _storage[cKey]) {
                        case ("&", nil): _storage[cKey] = NSMutableArray()
                        case (_, nil):   _storage[cKey] = NSMutableDictionary()
                        default: break
                        }
                        storage = _storage[cKey]!
                    case let _storage as NSMutableArray:
                        switch (nKey, _storage.lastObject) {
                        case ("&", nil): _storage.add(NSMutableArray())
                        case (_, nil):   _storage.add(NSMutableDictionary())
                        default: break
                        }
                        storage = _storage.lastObject!
                    default: break

                    }

                } else {    // storage에 적재
                    switch storage {
                    case let storage as NSMutableDictionary:
                        storage.setValue(val, forKey: cKey)
                    case let storage as NSMutableArray:
                        storage.add(val)
                    default: break
                    }
                }

            }

            return accu

        } as? [String: Any]

}

func test() {
  print(
    parse(qs: "param[url]=https://www.example.com&param[title]=XXX 이벤트&param[err]=&param[test][]=tesvale&param[test][]=tesvale2&param[a][][][kk]=2&param[a][][][ff]=3")
  )
  print(
    parse(qs: "name=kang&gae=39")
  )
}

/*
Optional(["param": {
    a =     (
                (
                        {
                ff = 3;
                kk = 2;
            }
        )
    );
    err = "";
    test =     (
        tesvale,
        tesvale2
    );
    title = "XXX \Uc774\Ubca4\Ud2b8";
    url = "https://www.example.com";
}])
Optional(["name": kang, "gae": 39])
*/