//    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/>.

// Generic, cross-platform tun interface that drives a TunBuilderBase API.
// Fully supports IPv6.  To make this work on a given platform, define
// a TunBuilderBase for the platform.

#ifndef OPENVPN_TUN_BUILDER_CLIENT_H
#define OPENVPN_TUN_BUILDER_CLIENT_H

#include <memory>

#include <openvpn/tun/client/tunprop.hpp>
#include <openvpn/tun/persist/tunpersist.hpp>
#include <openvpn/common/scoped_fd.hpp>
#include <openvpn/tun/tunio.hpp>

namespace openvpn {
  namespace TunBuilderClient {

    OPENVPN_EXCEPTION(tun_builder_error);

    // struct used to pass received tun packets
    struct PacketFrom
    {
      typedef std::unique_ptr<PacketFrom> SPtr;
      BufferAllocated buf;
    };

    // our TunPersist class, specialized for Unix file descriptors
    typedef TunPersistTemplate<ScopedFD> TunPersist;

    // A simplified tun interface where pre-existing
    // socket is provided.
    template <typename ReadHandler>
    class Tun : public TunIO<ReadHandler, PacketFrom, openvpn_io::posix::stream_descriptor>
    {
      typedef TunIO<ReadHandler, PacketFrom, openvpn_io::posix::stream_descriptor> Base;

    public:
      typedef RCPtr<Tun> Ptr;

      Tun(openvpn_io::io_context& io_context,
	  const int socket,
	  const bool retain_sd_arg,
	  const bool tun_prefix_arg,
	  ReadHandler read_handler_arg,
	  const Frame::Ptr& frame_arg,
	  const SessionStats::Ptr& stats_arg)
	: Base(read_handler_arg, frame_arg, stats_arg)
      {
	Base::stream = new openvpn_io::posix::stream_descriptor(io_context, socket);
	Base::name_ = "tun";
	Base::retain_stream = retain_sd_arg;
	Base::tun_prefix = tun_prefix_arg;
      }

      ~Tun() { Base::stop(); }
    };

    // A factory for the Client class
    class ClientConfig : public TunClientFactory
    {
    public:
      typedef RCPtr<ClientConfig> Ptr;

      TunProp::Config tun_prop;
      int n_parallel;            // number of parallel async reads on tun socket
      bool retain_sd;
      bool tun_prefix;
      Frame::Ptr frame;
      SessionStats::Ptr stats;
      EmulateExcludeRouteFactory::Ptr eer_factory;
      TunPersist::Ptr tun_persist;
      TunBuilderBase* builder;

      static Ptr new_obj()
      {
	return new ClientConfig;
      }

      TunClient::Ptr new_tun_client_obj(openvpn_io::io_context& io_context,
						TunClientParent& parent,
						TransportClient* transcli) override;

      void finalize(const bool disconnected) override
      {
	if (disconnected)
	  tun_persist.reset();
      }

    private:
      ClientConfig()
	: n_parallel(8), retain_sd(false), tun_prefix(false), builder(nullptr) {}
    };

    // The tun interface
    class Client : public TunClient
    {
      friend class ClientConfig;  // calls constructor
      friend class TunIO<Client*, PacketFrom, openvpn_io::posix::stream_descriptor>;  // calls tun_read_handler

      typedef Tun<Client*> TunImpl;

    public:
      virtual void tun_start(const OptionList& opt, TransportClient& transcli, CryptoDCSettings&) override
      {
	if (!impl)
	  {
	    halt = false;
	    if (config->tun_persist)
	      tun_persist = config->tun_persist; // long-term persistent
	    else
	      tun_persist.reset(new TunPersist(false, config->retain_sd, config->builder)); // short-term

	    try {
	      int sd = -1;
	      const IP::Addr server_addr = transcli.server_endpoint_addr();

	      // Check if persisted tun session matches properties of to-be-created session
	      if (tun_persist->use_persisted_tun(server_addr, config->tun_prop, opt))
		{
		  sd = tun_persist->obj();
		  state = tun_persist->state();
		  OPENVPN_LOG("TunPersist: reused tun context");

		  // indicate reconnection with persisted state
		  config->builder->tun_builder_establish_lite();
		}
	      else
		{
		  TunBuilderBase* tb = config->builder;

		  // reset target tun builder object
		  if (!tb->tun_builder_new())
		    throw tun_builder_error("tun_builder_new failed");

		  // notify parent
		  parent.tun_pre_tun_config();

		  // configure the tun builder
		  TunProp::configure_builder(tb, state.get(), config->stats.get(), server_addr,
					     config->tun_prop, opt, config->eer_factory.get(), false);

		  // start tun
		  sd = tb->tun_builder_establish();
		}

	      if (sd == -1)
		{
		  parent.tun_error(Error::TUN_IFACE_CREATE, "cannot acquire tun interface socket");
		  return;
		}

	      // persist state
	      if (tun_persist->persist_tun_state(sd, state))
		  OPENVPN_LOG("TunPersist: saving tun context:" << std::endl << tun_persist->options());

	      impl.reset(new TunImpl(io_context,
				     sd,
				     true,
				     config->tun_prefix,
				     this,
				     config->frame,
				     config->stats
				     ));
	      impl->start(config->n_parallel);

	      // signal that we are connected
	      parent.tun_connected();
	    }
	    catch (const std::exception& e)
	      {
		if (tun_persist)
		  tun_persist->close();
		stop();
		parent.tun_error(Error::TUN_SETUP_FAILED, e.what());
	      }
	  }
      }

      virtual bool tun_send(BufferAllocated& buf) override
      {
	return send(buf);
      }

      virtual std::string tun_name() const override
      {
	if (impl)
	  return impl->name();
	else
	  return "UNDEF_TUN";
      }

      virtual std::string vpn_ip4() const override
      {
	if (state->vpn_ip4_addr.specified())
	  return state->vpn_ip4_addr.to_string();
	else
	  return "";
      }

      virtual std::string vpn_ip6() const override
      {
	if (state->vpn_ip6_addr.specified())
	  return state->vpn_ip6_addr.to_string();
	else
	  return "";
      }

      virtual std::string vpn_gw4() const override
      {
	if (state->vpn_ip4_gw.specified())
	  return state->vpn_ip4_gw.to_string();
	else
	  return "";
      }

      virtual std::string vpn_gw6() const override
      {
	if (state->vpn_ip6_gw.specified())
	  return state->vpn_ip6_gw.to_string();
	else
	  return "";
      }

      virtual void set_disconnect() override
      {
	if (tun_persist)
	  tun_persist->set_disconnect();
      }

      virtual void stop() override { stop_(); }
      virtual ~Client() { stop_(); }

    private:
      Client(openvpn_io::io_context& io_context_arg,
	     ClientConfig* config_arg,
	     TunClientParent& parent_arg)
	:  io_context(io_context_arg),
	   config(config_arg),
	   parent(parent_arg),
	   halt(false),
	   state(new TunProp::State())
      {
      }

      bool send(Buffer& buf)
      {
	if (impl)
	  return impl->write(buf);
	else
	  return false;
      }

      void tun_read_handler(PacketFrom::SPtr& pfp) // called by TunImpl
      {
	parent.tun_recv(pfp->buf);
      }

      void tun_error_handler(const Error::Type errtype, // called by TunImpl
			     const openvpn_io::error_code* error)
      {
      }

      void stop_()
      {
	if (!halt)
	  {
	    halt = true;

	    // stop tun
	    if (impl)
	      impl->stop();
	    tun_persist.reset();
	  }
      }


      openvpn_io::io_context& io_context;
      TunPersist::Ptr tun_persist; // owns the tun socket descriptor
      ClientConfig::Ptr config;
      TunClientParent& parent;
      TunImpl::Ptr impl;
      bool halt;
      TunProp::State::Ptr state;
    };

    inline TunClient::Ptr ClientConfig::new_tun_client_obj(openvpn_io::io_context& io_context,
							   TunClientParent& parent,
							   TransportClient* transcli)
    {
      return TunClient::Ptr(new Client(io_context, this, parent));
    }

  }
}

#endif