//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012-2022 OpenVPN Inc.
//
//    This program is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Affero General Public License Version 3
//    as published by the Free Software Foundation.
//
//    This program is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//    GNU Affero General Public License for more details.
//
//    You should have received a copy of the GNU Affero General Public License
//    along with this program in the COPYING file.
//    If not, see <http://www.gnu.org/licenses/>.

// Encapsulate the state of a static or dynamic authentication challenge.

#ifndef OPENVPN_AUTH_CR_H
#define OPENVPN_AUTH_CR_H

#include <string>
#include <sstream>
#include <vector>

#include <openvpn/common/exception.hpp>
#include <openvpn/common/base64.hpp>
#include <openvpn/common/split.hpp>
#include <openvpn/common/rc.hpp>
#include <openvpn/common/string.hpp>

// Static Challenge response:
//   SCRV1:<BASE64_PASSWORD>:<BASE64_RESPONSE>
//
// Dynamic Challenge:
//   CRV1:<FLAGS>:<STATE_ID>:<BASE64_USERNAME>:<CHALLENGE_TEXT>
//   FLAGS is a comma-separated list of options:
//     E -- echo
//     R -- response required
//
// Dynamic Challenge response:
//   Username: [username decoded from username_base64]
//   Password: CRV1::<STATE_ID>::<RESPONSE_TEXT>

namespace openvpn {
class ChallengeResponse : public RC<thread_unsafe_refcount>
{
  public:
    typedef RCPtr<ChallengeResponse> Ptr;

    OPENVPN_SIMPLE_EXCEPTION(dynamic_challenge_parse_error);
    OPENVPN_SIMPLE_EXCEPTION(static_challenge_parse_error);

    ChallengeResponse()
        : echo(false), response_required(false)
    {
    }

    explicit ChallengeResponse(const std::string &cookie)
        : echo(false), response_required(false)
    {
        init(cookie);
    }

    ChallengeResponse(const std::string &cookie, const std::string &user)
        : echo(false), response_required(false)
    {
        if (!is_dynamic(cookie) && cookie.find_first_of(':') == std::string::npos)
        {
            state_id = cookie;
            username = user;
        }
        else
            init(cookie);
    }

    void init(const std::string &cookie)
    {
        typedef std::vector<std::string> StringList;
        StringList sl;
        sl.reserve(5);
        Split::by_char_void<StringList, NullLex, Split::NullLimit>(sl, cookie, ':', 0, 4);
        if (sl.size() != 5)
            throw dynamic_challenge_parse_error();
        if (sl[0] != "CRV1")
            throw dynamic_challenge_parse_error();

        // parse options
        {
            StringList opt;
            opt.reserve(2);
            Split::by_char_void<StringList, NullLex, Split::NullLimit>(opt, sl[1], ',');
            for (StringList::const_iterator i = opt.begin(); i != opt.end(); ++i)
            {
                if (*i == "E")
                    echo = true;
                else if (*i == "R")
                    response_required = true;
            }
        }

        // save state ID
        state_id = sl[2];

        // save username
        try
        {
            username = base64->decode(sl[3]);
        }
        catch (const Base64::base64_decode_error &)
        {
            throw dynamic_challenge_parse_error();
        }

        // save challenge
        challenge_text = sl[4];
    }

    static bool is_dynamic(const std::string &s)
    {
        return string::starts_with(s, "CRV1:");
    }

    static bool is_static(const std::string &s)
    {
        return string::starts_with(s, "SCRV1:");
    }

    static void validate_dynamic(const std::string &cookie)
    {
        ChallengeResponse cr(cookie);
    }

    std::string construct_dynamic_password(const std::string &response) const
    {
        std::ostringstream os;
        os << "CRV1::" << state_id << "::" << response;
        return os.str();
    }

    static std::string construct_static_password(const std::string &password,
                                                 const std::string &response)
    {
        std::ostringstream os;
        os << "SCRV1:" << base64->encode(password) << ':' << base64->encode(response);
        return os.str();
    }

    static void parse_static_cookie(const std::string &cookie,
                                    std::string &password,
                                    std::string &response)
    {
        typedef std::vector<std::string> StringList;
        StringList sl;
        sl.reserve(3);
        Split::by_char_void<StringList, NullLex, Split::NullLimit>(sl, cookie, ':');
        if (sl.size() != 3)
            throw static_challenge_parse_error();
        if (sl[0] != "SCRV1")
            throw static_challenge_parse_error();

        // get password
        try
        {
            password = base64->decode(sl[1]);
        }
        catch (const Base64::base64_decode_error &)
        {
            throw static_challenge_parse_error();
        }

        // get response
        try
        {
            response = base64->decode(sl[2]);
        }
        catch (const Base64::base64_decode_error &)
        {
            throw static_challenge_parse_error();
        }
    }

    static std::string generate_dynamic_challenge(const std::string &session_token,
                                                  const std::string &username,
                                                  const std::string &challenge,
                                                  const bool echo,
                                                  const bool response_required)
    {
        std::ostringstream os;
        bool comma = false;
        os << "CRV1:";
        if (echo)
        {
            if (comma)
                os << ",";
            os << "E";
            comma = true;
        }
        if (response_required)
        {
            if (comma)
                os << ",";
            os << "R";
            comma = true;
        }
        os << ':' << session_token;
        os << ':' << base64->encode(username);
        os << ':' << challenge;
        return os.str();
    }

    const std::string &get_state_id() const
    {
        return state_id;
    }
    const std::string &get_username() const
    {
        return username;
    }
    bool get_echo() const
    {
        return echo;
    }
    bool get_response_required() const
    {
        return response_required;
    }
    const std::string &get_challenge_text() const
    {
        return challenge_text;
    }

  private:
    bool echo;
    bool response_required;
    std::string state_id;
    std::string username;
    std::string challenge_text;
};
} // namespace openvpn

#endif