/**
 *
 * \section COPYRIGHT
 *
 * Copyright 2013-2017 Software Radio Systems Limited
 *
 * \section LICENSE
 *
 * This file is part of srsLTE.
 *
 * srsLTE is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of
 * the License, or (at your option) any later version.
 *
 * srsLTE 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.
 *
 * A copy of the GNU Affero General Public License can be found in
 * the LICENSE file in the top-level directory of this distribution
 * and at http://www.gnu.org/licenses/.
 *
 */

#include "srsepc/hdr/spgw/gtpc.h"
#include <algorithm>
#include <fcntl.h>
#include <inttypes.h> // for printing uint64_t
#include <linux/if.h>
#include <linux/if_tun.h>
#include <linux/ip.h>
#include <netinet/in.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/un.h>

namespace srsepc {

/**********************************************
 *
 * GTP-C class that handles the GTP-C protocol
 * comminication with the MME
 *
 **********************************************/
spgw::gtpc::gtpc() : m_h_next_ue_ip(0), m_next_ctrl_teid(1), m_next_user_teid(1)
{
  return;
}

spgw::gtpc::~gtpc()
{
  return;
}

int spgw::gtpc::init(spgw_args_t* args, spgw* spgw, gtpu_interface_gtpc* gtpu, srslte::log_filter* gtpc_log)
{
  srslte::error_t err;
  m_pool = srslte::byte_buffer_pool::get_instance();

  // Init log
  m_gtpc_log = gtpc_log;

  // Init interfaces
  m_spgw = spgw;
  m_gtpu = gtpu;

  // Init IP pool
  err = init_ue_ip(args);
  if (err != srslte::ERROR_NONE) {
    m_gtpc_log->console("Could not initialize the IP pool.\n");
    return -1;
  }

  m_gtpc_log->info("SPGW S11 Initialized.\n");
  m_gtpc_log->console("SPGW S11 Initialized.\n");
  return 0;
}

void spgw::gtpc::stop()
{
  std::map<uint32_t, spgw_tunnel_ctx*>::iterator it = m_teid_to_tunnel_ctx.begin();
  while (it != m_teid_to_tunnel_ctx.end()) {
    m_gtpc_log->info("Deleting SP-GW GTP-C Tunnel. IMSI: %lu\n", it->second->imsi);
    m_gtpc_log->console("Deleting SP-GW GTP-C Tunnel. IMSI: %lu\n", it->second->imsi);
    delete it->second;
    m_teid_to_tunnel_ctx.erase(it++);
  }
  return;
}

void spgw::gtpc::handle_s11_pdu(srslte::gtpc_pdu* pdu, srslte::gtpc_pdu* reply_pdu)
{
  m_gtpc_log->console("Received GTP-C PDU. Message type: %s\n", srslte::gtpc_msg_type_to_str(pdu->header.type));
  m_gtpc_log->debug("Received GTP-C PDU. Message type: %s\n", srslte::gtpc_msg_type_to_str(pdu->header.type));
  switch (pdu->header.type) {
    case srslte::GTPC_MSG_TYPE_CREATE_SESSION_REQUEST:
      handle_create_session_request(pdu->choice.create_session_request, reply_pdu);
      break;
    case srslte::GTPC_MSG_TYPE_MODIFY_BEARER_REQUEST:
      handle_modify_bearer_request(pdu->header, pdu->choice.modify_bearer_request, reply_pdu);
      break;
    case srslte::GTPC_MSG_TYPE_DELETE_SESSION_REQUEST:
      handle_delete_session_request(pdu->header, pdu->choice.delete_session_request, reply_pdu);
      break;
    case srslte::GTPC_MSG_TYPE_RELEASE_ACCESS_BEARERS_REQUEST:
      handle_release_access_bearers_request(pdu->header, pdu->choice.release_access_bearers_request, reply_pdu);
      break;
    default:
      m_gtpc_log->error("Unhandled GTP-C message type\n");
  }
  return;
}

void spgw::gtpc::handle_create_session_request(const struct srslte::gtpc_create_session_request& cs_req, srslte::gtpc_pdu *cs_resp_pdu)
{
  m_gtpc_log->info("SPGW Received Create Session Request\n");
  spgw_tunnel_ctx_t* tunnel_ctx;
  int                default_bearer_id = 5;
  // Check if IMSI has active GTP-C and/or GTP-U
  bool gtpc_present = m_imsi_to_ctr_teid.count(cs_req.imsi);
  if (gtpc_present) {
    m_gtpc_log->console("SPGW: GTP-C context for IMSI %015lu already exists.\n", cs_req.imsi);
    delete_gtpc_ctx(m_imsi_to_ctr_teid[cs_req.imsi]);
    m_gtpc_log->console("SPGW: Deleted previous context.\n");
  }

  m_gtpc_log->info("Creating new GTP-C context\n");
  tunnel_ctx = create_gtpc_ctx(cs_req);

  // Create session response message
  srslte::gtpc_header*                  header  = &cs_resp_pdu->header;
  srslte::gtpc_create_session_response* cs_resp = &cs_resp_pdu->choice.create_session_response;

  // Setup GTP-C header
  header->piggyback    = false;
  header->teid_present = true;
  header->teid         = tunnel_ctx->dw_ctrl_fteid.teid; // Send create session response to the UE's MME Ctrl TEID
  header->type         = srslte::GTPC_MSG_TYPE_CREATE_SESSION_RESPONSE;

  // Initialize to zero
  bzero(cs_resp, sizeof(struct srslte::gtpc_create_session_response));
  // Setup Cause
  cs_resp->cause.cause_value = srslte::GTPC_CAUSE_VALUE_REQUEST_ACCEPTED;
  // Setup sender F-TEID (ctrl)
  cs_resp->sender_f_teid.ipv4_present = true;
  cs_resp->sender_f_teid              = tunnel_ctx->up_ctrl_fteid;

  // Bearer context created
  cs_resp->eps_bearer_context_created.ebi                     = default_bearer_id;
  cs_resp->eps_bearer_context_created.cause.cause_value       = srslte::GTPC_CAUSE_VALUE_REQUEST_ACCEPTED;
  cs_resp->eps_bearer_context_created.s1_u_sgw_f_teid_present = true;
  cs_resp->eps_bearer_context_created.s1_u_sgw_f_teid         = tunnel_ctx->up_user_fteid;

  // Fill in the PAA
  cs_resp->paa_present      = true;
  cs_resp->paa.pdn_type     = srslte::GTPC_PDN_TYPE_IPV4;
  cs_resp->paa.ipv4_present = true;
  cs_resp->paa.ipv4         = tunnel_ctx->ue_ipv4;
  m_gtpc_log->info("Sending Create Session Response\n");

  // Send Create session response to MME
  return;
}

void spgw::gtpc::handle_modify_bearer_request(const struct srslte::gtpc_header&                mb_req_hdr,
                                              const struct srslte::gtpc_modify_bearer_request& mb_req,
                                              srslte::gtpc_pdu*                                mb_resp_pdu)
{
  m_gtpc_log->info("Received Modified Bearer Request\n");

  // Get control tunnel info from mb_req PDU
  uint32_t                                         ctrl_teid = mb_req_hdr.teid;
  std::map<uint32_t, spgw_tunnel_ctx_t*>::iterator tunnel_it = m_teid_to_tunnel_ctx.find(ctrl_teid);
  if (tunnel_it == m_teid_to_tunnel_ctx.end()) {
    m_gtpc_log->warning("Could not find TEID %d to modify\n", ctrl_teid);
    return;
  }
  spgw_tunnel_ctx_t* tunnel_ctx = tunnel_it->second;

  // Store user DW link TEID
  tunnel_ctx->dw_user_fteid.teid = mb_req.eps_bearer_context_to_modify.s1_u_enb_f_teid.teid;
  tunnel_ctx->dw_user_fteid.ipv4 = mb_req.eps_bearer_context_to_modify.s1_u_enb_f_teid.ipv4;
  // Set up actual tunnel
  m_gtpc_log->info("Setting Up GTP-U tunnel. Tunnel info: \n");
  struct in_addr addr;
  addr.s_addr = tunnel_ctx->ue_ipv4;
  m_gtpc_log->info("IMSI: %lu, UE IP: %s \n", tunnel_ctx->imsi, inet_ntoa(addr));
  m_gtpc_log->info("S-GW Rx Ctrl TEID 0x%x, MME Rx Ctrl TEID 0x%x\n", tunnel_ctx->up_ctrl_fteid.teid,
                   tunnel_ctx->dw_ctrl_fteid.teid);
  m_gtpc_log->info("S-GW Rx Ctrl IP (NA), MME Rx Ctrl IP (NA)\n");

  struct in_addr addr2;
  addr2.s_addr = tunnel_ctx->up_user_fteid.ipv4;
  m_gtpc_log->info("S-GW Rx User TEID 0x%x, S-GW Rx User IP %s\n", tunnel_ctx->up_user_fteid.teid, inet_ntoa(addr2));

  struct in_addr addr3;
  addr3.s_addr = tunnel_ctx->dw_user_fteid.ipv4;
  m_gtpc_log->info("eNB Rx User TEID 0x%x, eNB Rx User IP %s\n", tunnel_ctx->dw_user_fteid.teid, inet_ntoa(addr3));

  // Setup IP to F-TEID map
  m_gtpu->modify_gtpu_tunnel(tunnel_ctx->ue_ipv4, tunnel_ctx->dw_user_fteid, tunnel_ctx->up_ctrl_fteid.teid);

  // Setting up Modify bearer response PDU
  // Header
  srslte::gtpc_header* header = &mb_resp_pdu->header;
  header->piggyback           = false;
  header->teid_present        = true;
  header->teid                = tunnel_ctx->dw_ctrl_fteid.teid;
  header->type                = srslte::GTPC_MSG_TYPE_MODIFY_BEARER_RESPONSE;

  // PDU
  srslte::gtpc_modify_bearer_response* mb_resp           = &mb_resp_pdu->choice.modify_bearer_response;
  mb_resp->cause.cause_value                             = srslte::GTPC_CAUSE_VALUE_REQUEST_ACCEPTED;
  mb_resp->eps_bearer_context_modified.ebi               = tunnel_ctx->ebi;
  mb_resp->eps_bearer_context_modified.cause.cause_value = srslte::GTPC_CAUSE_VALUE_REQUEST_ACCEPTED;
  
  //Send Modify Bearer Response PDU
  return;
}

void spgw::gtpc::handle_delete_session_request(const srslte::gtpc_header&                 header,
                                               const srslte::gtpc_delete_session_request& del_req_pdu,
                                               srslte::gtpc_pdu*                          del_resp_pdu)
{
  uint32_t                                         ctrl_teid = header.teid;
  std::map<uint32_t, spgw_tunnel_ctx_t*>::iterator tunnel_it = m_teid_to_tunnel_ctx.find(ctrl_teid);
  if (tunnel_it == m_teid_to_tunnel_ctx.end()) {
    m_gtpc_log->warning("Could not find TEID 0x%x to delete session\n", ctrl_teid);
    return;
  }
  spgw_tunnel_ctx_t* tunnel_ctx = tunnel_it->second;
  in_addr_t          ue_ipv4    = tunnel_ctx->ue_ipv4;
  m_gtpu->delete_gtpu_tunnel(ue_ipv4);
  delete_gtpc_ctx(ctrl_teid);
  return;
}

void spgw::gtpc::handle_release_access_bearers_request(const srslte::gtpc_header&                         header,
                                                       const srslte::gtpc_release_access_bearers_request& rel_req,
                                                       srslte::gtpc_pdu*                                  rel_resp_pdu)
{
  // Find tunel ctxt
  uint32_t                                         ctrl_teid = header.teid;
  std::map<uint32_t, spgw_tunnel_ctx_t*>::iterator tunnel_it = m_teid_to_tunnel_ctx.find(ctrl_teid);
  if (tunnel_it == m_teid_to_tunnel_ctx.end()) {
    m_gtpc_log->warning("Could not find TEID 0x%x to release bearers\n", ctrl_teid);
    return;
  }
  spgw_tunnel_ctx_t* tunnel_ctx = tunnel_it->second;
  in_addr_t          ue_ipv4    = tunnel_ctx->ue_ipv4;

  // Delete data tunnel & do NOT delete control tunnel
  m_gtpu->delete_gtpu_tunnel(ue_ipv4);
  return;
}

/*
 * Context management functions
 */
spgw_tunnel_ctx_t* spgw::gtpc::create_gtpc_ctx(const struct srslte::gtpc_create_session_request& cs_req)
{
  // Setup uplink control TEID
  uint64_t spgw_uplink_ctrl_teid = get_new_ctrl_teid();
  // Setup uplink user TEID
  uint64_t spgw_uplink_user_teid = get_new_user_teid();
  // Allocate UE IP
  in_addr_t ue_ip = get_new_ue_ipv4();

  uint8_t default_bearer_id = 5;

  m_gtpc_log->console("SPGW: Allocated Ctrl TEID %" PRIu64 "\n", spgw_uplink_ctrl_teid);
  m_gtpc_log->console("SPGW: Allocated User TEID %" PRIu64 "\n", spgw_uplink_user_teid);
  struct in_addr ue_ip_;
  ue_ip_.s_addr = ue_ip;
  m_gtpc_log->console("SPGW: Allocate UE IP %s\n", inet_ntoa(ue_ip_));

  // Save the UE IP to User TEID map
  spgw_tunnel_ctx_t* tunnel_ctx = new spgw_tunnel_ctx_t;

  tunnel_ctx->imsi           = cs_req.imsi;
  tunnel_ctx->ebi            = default_bearer_id;

  tunnel_ctx->up_ctrl_fteid.teid = spgw_uplink_ctrl_teid;
  tunnel_ctx->ue_ipv4            = ue_ip;
  tunnel_ctx->up_user_fteid.teid = spgw_uplink_user_teid;
  tunnel_ctx->up_user_fteid.ipv4 = m_gtpu->get_s1u_addr();
  tunnel_ctx->dw_ctrl_fteid.teid = cs_req.sender_f_teid.teid;
  tunnel_ctx->dw_ctrl_fteid.ipv4 = cs_req.sender_f_teid.ipv4;
  bzero(&tunnel_ctx->dw_user_fteid, sizeof(srslte::gtp_fteid_t));

  m_teid_to_tunnel_ctx.insert(std::pair<uint32_t, spgw_tunnel_ctx_t*>(spgw_uplink_ctrl_teid, tunnel_ctx));
  m_imsi_to_ctr_teid.insert(std::pair<uint64_t, uint32_t>(cs_req.imsi, spgw_uplink_ctrl_teid));
  return tunnel_ctx;
}

bool spgw::gtpc::delete_gtpc_ctx(uint32_t ctrl_teid)
{
  spgw_tunnel_ctx_t* tunnel_ctx;
  if (!m_teid_to_tunnel_ctx.count(ctrl_teid)) {
    m_gtpc_log->error("Could not find GTP context to delete.\n");
    return false;
  }
  tunnel_ctx = m_teid_to_tunnel_ctx[ctrl_teid];

  // Remove Ctrl TEID from IMSI to control TEID map
  m_imsi_to_ctr_teid.erase(tunnel_ctx->imsi);

  // Remove GTP context from control TEID mapping
  m_teid_to_tunnel_ctx.erase(ctrl_teid);
  delete tunnel_ctx;
  return true;
}

} // namespace srsepc