//    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) 2012-2020 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/>.
//

// Name Resolution Policy Table (NRPT) utilities for Windows

#ifndef OPENVPN_TUN_WIN_NRPT_H
#define OPENVPN_TUN_WIN_NRPT_H

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

#include <openvpn/common/exception.hpp>
#include <openvpn/common/string.hpp>
#include <openvpn/common/wstring.hpp>
#include <openvpn/common/action.hpp>
#include <openvpn/win/reg.hpp>
#include <openvpn/win/winerr.hpp>

namespace openvpn {
  namespace TunWin {

    // NRPT rules described here: https://msdn.microsoft.com/en-us/library/ff957356.aspx
    class NRPT
    {
    public:
      OPENVPN_EXCEPTION(nrpt_error);

      static void create_rule(const std::vector<std::string> names, const std::vector<std::string> dns_servers)
      {
	Win::RegKey key;

	for (size_t i = 0; i < names.size(); ++ i)
	  {
	    // open/create the key
	    {
	      std::ostringstream ss;
	      ss << dnsPolicyConfig() << "\\" << policyPrefix() << "-" << i;
	      auto key_name = ss.str();

	      const LONG status = ::RegCreateKeyA(HKEY_LOCAL_MACHINE, key_name.c_str(), key.ref());
	      check_reg_error<nrpt_error>(status, key_name);
	    }

	    // Name
	    {
	      std::wstring name(wstring::from_utf8(names[i]));
	      name += L'\0';
	      const LONG status = ::RegSetValueExW(key(),
						   L"Name",
						   0,
						   REG_MULTI_SZ,
						   (const BYTE *)name.c_str(),
						   (name.length()+1)*2);
	      check_reg_error<nrpt_error>(status, "Name");
	    }

	    // GenericDNSServers
	    {
	      const std::wstring dns_servers_joined = wstring::from_utf8(string::join(dns_servers, ";"));
	      const LONG status = ::RegSetValueExW(key(),
						   L"GenericDNSServers",
						   0,
						   REG_SZ,
						   (const BYTE *)dns_servers_joined.c_str(),
						   (dns_servers_joined.length()+1)*2);
	      check_reg_error<nrpt_error>(status, "GenericDNSServers");
	    }

	    // ConfigOptions
	    {
	      const DWORD value = 0x8; // Only the Generic DNS server option (that is, the option defined in section 2.2.2.13) is specified.
	      const LONG status = ::RegSetValueExW(key(),
						   L"ConfigOptions",
						   0,
						   REG_DWORD,
						   (const BYTE *)&value,
						   sizeof(value));
	      check_reg_error<nrpt_error>(status, "ConfigOptions");
	    }

	    // Version
	    {
	      const DWORD value = 0x2;
	      const LONG status = ::RegSetValueExW(key(),
						   L"Version",
						   0,
						   REG_DWORD,
						   (const BYTE *)&value,
						   sizeof(value));
	      check_reg_error<nrpt_error>(status, "Version");
	    }
	  }
      }

      static bool delete_rule()
      {
	Win::RegKeyEnumerator keys(HKEY_LOCAL_MACHINE, dnsPolicyConfig());

	for (const auto& key : keys)
	  {
	    // remove only own policies
	    if (key.find(policyPrefix()) == std::string::npos)
	      continue;

	    std::ostringstream ss;
	    ss << dnsPolicyConfig() << "\\" << key;
	    auto path = ss.str();
	    ::RegDeleteTreeA(HKEY_LOCAL_MACHINE, path.c_str());
	  }

	return true;
      }

    private:
      static const char *dnsPolicyConfig()
      {
	static const char subkey[] = "SYSTEM\\CurrentControlSet\\Services\\Dnscache\\Parameters\\DnsPolicyConfig";
	return subkey;
      }

      static const char *policyPrefix()
      {
	static const char prefix[] = "OpenVPNDNSRouting";
	return prefix;
      }

    public:
      class ActionCreate : public Action
      {
      public:
	ActionCreate(const std::vector<std::string>& names_arg,
		     const std::vector<std::string>& dns_servers_arg)
	  : names(names_arg),
	    dns_servers(dns_servers_arg)
	{
	}

	virtual void execute(std::ostream& log) override
	{
	  log << to_string() << std::endl;
	  create_rule(names, dns_servers);
	}

	virtual std::string to_string() const override
	{
	  std::ostringstream os;
	  os << "NRPT::ActionCreate"
	     << " names=[" << string::join(names, ",") << "]"
	     << " dns_servers=[" << string::join(dns_servers, ",") << "]";
	  return os.str();
	}

      private:
	const std::vector<std::string> names;
	const std::vector<std::string> dns_servers;
      };

      class ActionDelete : public Action
      {
      public:
	virtual void execute(std::ostream& log) override
	{
	  log << to_string() << std::endl;
	  delete_rule();
	}

	virtual std::string to_string() const override
	{
	  return "NRPT::ActionDelete";
	}
      };

    };

  }
}

#endif