#include <stdlib.h>
#include <assert.h>

#include "stellar.h"
#include "tcp_utils.h"
#include "udp_utils.h"
#include "id_generator.h"
#include "session_pool.h"
#include "session_table.h"
#include "session_timer.h"
#include "session_manager.h"
#include "session_transition.h"
#include "evicted_session_filter.h"
#include "duplicated_packet_filter.h"

struct session_manager
{
     // max session number
     uint64_t max_tcp_session_num;
     uint64_t max_udp_session_num;
     // session overload
     uint8_t tcp_overload_evict_old_sess; // 1: evict old session, 0: bypass new session
     uint8_t udp_overload_evict_old_sess; // 1: evict old session, 0: bypass new session
     // TCP timeout
     uint64_t tcp_init_timeout;           // range: [1, 60000]
     uint64_t tcp_handshake_timeout;      // range: [1, 60000]
     uint64_t tcp_data_timeout;           // range: [1, 15999999000]
     uint64_t tcp_half_closed_timeout;    // range: [1, 604800000]
     uint64_t tcp_time_wait_timeout;      // range: [1, 600000]
     uint64_t tcp_discard_timeout;        // range: [1, 15999999000]
     uint64_t tcp_unverified_rst_timeout; // range: [1, 600000]
     // UDP timeout
     uint64_t udp_data_timeout; // range: [1, 15999999000]
     // TCP reassembly
     uint32_t tcp_reassembly_max_timeout;  // range: [1, 60000] (ms)
     uint32_t tcp_reassembly_max_segments; // range: [2, 32]

     struct session_pool *sess_pool;
     struct session_table *tcp_sess_table;
     struct session_table *udp_sess_table;
     struct session_timer *sess_timer;
     struct list_head evicte_queue;

     struct duplicated_packet_filter *dup_pkt_filter;
     struct evicted_session_filter *evicte_sess_filter;

     struct session_manager_stat stat;
};

#define EVICTE_SESSION_BURST (RX_BURST_MAX)

// TODO
int check_options(const struct session_manager_options *opts)
{
     if (opts == NULL)
     {
          SESSION_LOG_ERROR("invalid options");
          return -1;
     }

     if (opts->tcp_init_timeout < 1 || opts->tcp_init_timeout > 60000)
     {
          SESSION_LOG_ERROR("invalid tcp_init_timeout: %lu, supported range: [1, 60000]", opts->tcp_init_timeout);
          return -1;
     }
     if (opts->tcp_handshake_timeout < 1 || opts->tcp_handshake_timeout > 60000)
     {
          SESSION_LOG_ERROR("invalid tcp_handshake_timeout: %lu, supported range: [1, 60000]", opts->tcp_handshake_timeout);
          return -1;
     }
     if (opts->tcp_data_timeout < 1 || opts->tcp_data_timeout > 15999999000)
     {
          SESSION_LOG_ERROR("invalid tcp_data_timeout: %lu, supported range: [1, 15999999000]", opts->tcp_data_timeout);
          return -1;
     }
     if (opts->tcp_half_closed_timeout < 1 || opts->tcp_half_closed_timeout > 604800000)
     {
          SESSION_LOG_ERROR("invalid tcp_half_closed_timeout: %lu, supported range: [1, 604800000]", opts->tcp_half_closed_timeout);
          return -1;
     }
     if (opts->tcp_time_wait_timeout < 1 || opts->tcp_time_wait_timeout > 600000)
     {
          SESSION_LOG_ERROR("invalid tcp_time_wait_timeout: %lu, supported range: [1, 600000]", opts->tcp_time_wait_timeout);
          return -1;
     }
     if (opts->tcp_discard_timeout < 1 || opts->tcp_discard_timeout > 15999999000)
     {
          SESSION_LOG_ERROR("invalid tcp_discard_timeout: %lu, supported range: [1, 15999999000]", opts->tcp_discard_timeout);
          return -1;
     }
     if (opts->tcp_unverified_rst_timeout < 1 || opts->tcp_unverified_rst_timeout > 600000)
     {
          SESSION_LOG_ERROR("invalid tcp_unverified_rst_timeout: %lu, supported range: [1, 600000]", opts->tcp_unverified_rst_timeout);
          return -1;
     }
     if (opts->udp_data_timeout < 1 || opts->udp_data_timeout > 15999999000)
     {
          SESSION_LOG_ERROR("invalid udp_data_timeout: %lu, supported range: [1, 15999999000]", opts->udp_data_timeout);
          return -1;
     }

     return 0;
}

/*
 * The next routines deal with comparing 32 bit unsigned ints
 * and worry about wraparound (automatic with unsigned arithmetic).
 */

static inline bool before(uint32_t seq1, uint32_t seq2)
{
     return (int32_t)(seq1 - seq2) < 0;
}

static void tcp_pcb_clean(struct tcp_pcb *pcb)
{
     if (pcb)
     {
          tcp_reassembly_free(pcb->c2s_assembler);
          tcp_reassembly_free(pcb->s2c_assembler);
     }
}

static int tcp_pcb_init(struct tcp_pcb *pcb, uint64_t max_timeout, uint64_t max_seg_num)
{
     pcb->c2s_assembler = tcp_reassembly_new(max_timeout, max_seg_num);
     pcb->s2c_assembler = tcp_reassembly_new(max_timeout, max_seg_num);
     if (pcb->c2s_assembler == NULL || pcb->s2c_assembler == NULL)
     {
          tcp_pcb_clean(pcb);
          return -1;
     }

     return 0;
}

static void tcp_pcb_update(struct tcp_pcb *pcb, enum session_dir dir, const struct pkt_layer *tcp_layer, uint64_t now)
{
     struct tcp_segment *seg;
     struct tcp_reassembly *assembler;
     struct tcphdr *hdr = (struct tcphdr *)tcp_layer->hdr_ptr;

     uint32_t seq = tcp_hdr_get_seq(hdr);
     uint32_t ack = tcp_hdr_get_ack(hdr);
     uint8_t flags = tcp_hdr_get_flags(hdr);
     uint32_t rcv_nxt;

     /*
      * https://www.rfc-editor.org/rfc/rfc5961#section-3.2
      *
      * If the RST bit is set and the sequence number exactly matches the
      * next expected sequence number (RCV.NXT), then TCP MUST reset the
      * connection.
      *
      * if fin is received, the expected sequence number should be increased by 1
      */
     uint16_t expect = 0;
     if (dir == SESSION_DIR_C2S)
     {
          pcb->c2s_seq = seq;
          pcb->c2s_ack = ack;
          assembler = pcb->c2s_assembler;

          expect = pcb->s2c_ack;
          expect += pcb->sub_state & TCP_S2C_FIN_RCVD ? 1 : 0;

          pcb->sub_state |= (flags & TH_SYN) ? TCP_SYN_RCVD : 0;
          pcb->sub_state |= (flags & TH_FIN) ? TCP_C2S_FIN_RCVD : 0;
          pcb->sub_state |= ((flags & TH_RST) && (seq == expect)) ? TCP_C2S_RST_RCVD : 0;
          pcb->sub_state |= ((flags & TH_RST) && (seq != expect)) ? TCP_C2S_UNVERIFIED_RST_RCVD : 0;
     }
     else
     {
          pcb->s2c_seq = seq;
          pcb->s2c_ack = ack;
          assembler = pcb->s2c_assembler;

          expect = pcb->c2s_ack;
          expect += pcb->sub_state & TCP_C2S_FIN_RCVD ? 1 : 0;

          pcb->sub_state |= (flags & TH_SYN) ? TCP_SYN_ACK_RCVD : 0;
          pcb->sub_state |= (flags & TH_FIN) ? TCP_S2C_FIN_RCVD : 0;
          pcb->sub_state |= ((flags & TH_RST) && (seq == expect)) ? TCP_S2C_RST_RCVD : 0;
          pcb->sub_state |= ((flags & TH_RST) && (seq != expect)) ? TCP_S2C_UNVERIFIED_RST_RCVD : 0;
     }

     if (flags & TH_SYN)
     {
          tcp_reassembly_set_recv_next(assembler, seq + 1);
     }

     seg = tcp_reassembly_expire(assembler, now);
     if (seg)
     {
          // TODO add metric (expire)
          tcp_segment_free(seg);
     }

     if (tcp_layer->pld_len)
     {
          rcv_nxt = tcp_reassembly_get_recv_next(assembler);
          if (seq == rcv_nxt)
          {
               pcb->order_seg.data = tcp_layer->pld_ptr;
               pcb->order_seg.len = tcp_layer->pld_len;
               tcp_reassembly_inc_recv_next(assembler, tcp_layer->pld_len);
          }
          else if (before(seq, rcv_nxt))
          {
               // TODO add metric (overlap)
          }
          else if ((seg = tcp_segment_new(seq, tcp_layer->pld_ptr, tcp_layer->pld_len)))
          {
               switch (tcp_reassembly_push(assembler, seg, now))
               {
               case -1:
                    // TODO add metric (assembler full)
                    tcp_segment_free(seg);
                    break;
               case 0:
                    // TODO add metric (assembler push success)
                    break;
               case 1:
                    // TODO add metric (assembler push success, overlap)
                    break;
               default:
                    assert(0);
                    break;
               }
          }
     }
}

/******************************************************************************
 * Stat
 ******************************************************************************/

static void session_stat_inc(struct session_stat *stat, enum session_state state)
{
     switch (state)
     {
     case SESSION_STATE_INIT:
          stat->nr_sess_init++;
          break;
     case SESSION_STATE_OPENING:
          stat->nr_sess_opening++;
          break;
     case SESSION_STATE_ACTIVE:
          stat->nr_sess_active++;
          break;
     case SESSION_STATE_CLOSING:
          stat->nr_sess_closing++;
          break;
     case SESSION_STATE_DISCARD:
          stat->nr_sess_discard++;
          break;
     case SESSION_STATE_CLOSED:
          stat->nr_sess_closed++;
          break;
     default:
          break;
     }
}

static void session_stat_dec(struct session_stat *stat, enum session_state state)
{
     switch (state)
     {
     case SESSION_STATE_INIT:
          stat->nr_sess_init--;
          break;
     case SESSION_STATE_OPENING:
          stat->nr_sess_opening--;
          break;
     case SESSION_STATE_ACTIVE:
          stat->nr_sess_active--;
          break;
     case SESSION_STATE_CLOSING:
          stat->nr_sess_closing--;
          break;
     case SESSION_STATE_DISCARD:
          stat->nr_sess_discard--;
          break;
     case SESSION_STATE_CLOSED:
          stat->nr_sess_closed--;
          break;
     default:
          break;
     }
}

static void session_stat_update(struct session_manager *mgr, struct session *sess, enum session_state curr_state, enum session_state next_state)
{
     switch (session_get_type(sess))
     {
     case SESSION_TYPE_TCP:
          session_stat_dec(&mgr->stat.tcp_sess, curr_state);
          session_stat_inc(&mgr->stat.tcp_sess, next_state);
          break;
     case SESSION_TYPE_UDP:
          session_stat_dec(&mgr->stat.udp_sess, curr_state);
          session_stat_inc(&mgr->stat.udp_sess, next_state);
          break;
     default:
          break;
     }
}

/******************************************************************************
 * Session Direction
 ******************************************************************************/

static enum session_dir identify_direction_by_port(uint16_t src_port, uint16_t dst_port)
{
     // big port is client
     if (src_port > dst_port)
     {
          return SESSION_DIR_C2S;
     }
     else if (src_port < dst_port)
     {
          return SESSION_DIR_S2C;
     }
     else
     {
          // if port is equal, first packet is C2S
          return SESSION_DIR_C2S;
     }
}

static enum session_dir identify_direction_by_history(const struct session *sess, const struct tuple6 *key)
{
     if (tuple6_cmp(session_get_tuple(sess), key) == 0)
     {
          return session_get_tuple_dir(sess);
     }
     else
     {
          return (session_get_tuple_dir(sess) == SESSION_DIR_C2S ? SESSION_DIR_S2C : SESSION_DIR_C2S);
     }
}

/******************************************************************************
 * Session Filter
 ******************************************************************************/

#define MAX_FILTER_NUM_PER_STAGE 4
enum filter_stage
{
     FILTER_STAGE_PRE_NEW_SESS,
     FILTER_STAGE_PRE_UPDATE_SESS,
     MAX_FILTER_STAGE,
};

// return 1: bypass
// return 0: not bypass
typedef int filter(struct session_manager *mgr, struct session *sess, const struct packet *pkt, const struct tuple6 *key, uint64_t now);

// on pre new session
static int session_manager_self_protection(struct session_manager *mgr, struct session *sess, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     struct session_manager_stat *stat = &mgr->stat;
     switch (key->ip_proto)
     {
     case IPPROTO_TCP:
          if (stat->tcp_sess.nr_sess_used >= mgr->max_tcp_session_num)
          {
               stat->evc_pkt.nr_pkts++;
               stat->evc_pkt.nr_bytes += packet_get_len(pkt);
               stat->tcp_sess.nr_new_sess_evicted++;
               return 1;
          }
          break;
     case IPPROTO_UDP:
          if (stat->udp_sess.nr_sess_used >= mgr->max_udp_session_num)
          {
               stat->evc_pkt.nr_pkts++;
               stat->evc_pkt.nr_bytes += packet_get_len(pkt);
               stat->udp_sess.nr_new_sess_evicted++;
               return 1;
          }
          break;
     default:
          break;
     }

     return 0;
}

// on pre new session
static int session_manager_filter_evicted_session(struct session_manager *mgr, struct session *sess, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     if (evicted_session_filter_lookup(mgr->evicte_sess_filter, key, now))
     {
          mgr->stat.evc_pkt.nr_pkts++;
          mgr->stat.evc_pkt.nr_bytes += packet_get_len(pkt);
          return 1;
     }

     return 0;
}

// on pre update session
static int session_manager_filter_duplicated_packet(struct session_manager *mgr, struct session *sess, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     enum session_dir dir = identify_direction_by_history(sess, key);
     if ((dir == SESSION_DIR_C2S && session_get_metric(sess, SESSION_METRIC_C2S_PACKETS) < 3) ||
         (dir == SESSION_DIR_S2C && session_get_metric(sess, SESSION_METRIC_S2C_PACKETS) < 3) ||
         (session_has_dup_traffic(sess) == 1))
     {
          if (duplicated_packet_filter_lookup(mgr->dup_pkt_filter, pkt, now))
          {
               mgr->stat.dup_pkt.nr_pkts++;
               mgr->stat.dup_pkt.nr_bytes += packet_get_len(pkt);
               session_set_dup_traffic(sess);
               return 1;
          }
          else
          {
               duplicated_packet_filter_add(mgr->dup_pkt_filter, pkt, now);
               return 0;
          }
     }

     return 0;
}

filter *smf[MAX_FILTER_STAGE][MAX_FILTER_NUM_PER_STAGE];

static void session_filter_init()
{
     for (int i = 0; i < MAX_FILTER_STAGE; i++)
     {
          for (int j = 0; j < MAX_FILTER_NUM_PER_STAGE; j++)
          {
               smf[i][j] = NULL;
          }
     }

     smf[FILTER_STAGE_PRE_NEW_SESS][0] = session_manager_self_protection;
     smf[FILTER_STAGE_PRE_NEW_SESS][1] = session_manager_filter_evicted_session;
     smf[FILTER_STAGE_PRE_NEW_SESS][2] = NULL;

     smf[FILTER_STAGE_PRE_UPDATE_SESS][0] = session_manager_filter_duplicated_packet;
     smf[FILTER_STAGE_PRE_UPDATE_SESS][1] = NULL;
}

// return 1: bypass packet
// return 0: not bypass packet
static int session_filter_run(struct session_manager *mgr, enum filter_stage stage, struct session *sess, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     filter **list = smf[stage];
     for (int i = 0; i < MAX_FILTER_NUM_PER_STAGE; i++)
     {
          if (list[i])
          {
               if (list[i](mgr, sess, pkt, key, now))
               {
                    return 1;
               }
          }
          else
          {
               break;
          }
     }

     return 0;
}

/******************************************************************************
 * Session Manager
 ******************************************************************************/

static void session_update(struct session *sess, enum session_state next_state, const struct packet *pkt, const struct tuple6 *key, enum session_dir dir, uint64_t now)
{
     if (session_get_state(sess) == SESSION_STATE_INIT)
     {
          session_set_tuple(sess, key);
          session_set_tuple_dir(sess, dir);
          session_set_timestamp(sess, SESSION_TIMESTAMP_NEW, now);
          switch (key->ip_proto)
          {
          case IPPROTO_TCP:
               session_set_type(sess, SESSION_TYPE_TCP);
               break;
          case IPPROTO_UDP:
               session_set_type(sess, SESSION_TYPE_UDP);
               break;
          default:
               assert(0);
               break;
          }
     }

     if (dir == SESSION_DIR_C2S)
     {
          session_inc_metric(sess, SESSION_METRIC_C2S_PACKETS, 1);
          session_inc_metric(sess, SESSION_METRIC_C2S_BYTES, packet_get_len(pkt));
          session_set_packet(sess, SESSION_PACKET_C2S_1ST, pkt);
     }
     else
     {
          session_inc_metric(sess, SESSION_METRIC_S2C_PACKETS, 1);
          session_inc_metric(sess, SESSION_METRIC_S2C_BYTES, packet_get_len(pkt));
          session_set_packet(sess, SESSION_PACKET_S2C_1ST, pkt);
     }
     session_set_packet(sess, SESSION_PACKET_CURRENT, pkt);
     session_set_cur_dir(sess, dir);
     session_set_timestamp(sess, SESSION_TIMESTAMP_LAST, now);
     session_set_state(sess, next_state);
}

static void session_manager_evicte_session(struct session_manager *mgr, struct session *sess, uint64_t now)
{
     if (sess == NULL)
     {
          return;
     }

     // when session add to evicted queue, session lifetime is over
     enum session_state curr_state = session_get_state(sess);
     enum session_state next_state = session_transition_run(curr_state, LRU_EVICT);
     session_transition_log(sess, curr_state, next_state, LRU_EVICT);
     session_set_state(sess, next_state);
     session_stat_update(mgr, sess, curr_state, next_state);

     session_timer_del(mgr->sess_timer, sess);
     session_set_closing_reason(sess, CLOSING_BY_EVICTED);
     list_add_tail(&sess->evicte, &mgr->evicte_queue);

     switch (session_get_type(sess))
     {
     case SESSION_TYPE_TCP:
          SESSION_LOG_DEBUG("evicte tcp old session: %lu", session_get_id(sess));
          mgr->stat.tcp_sess.nr_old_sess_evicted++;
          session_table_del(mgr->tcp_sess_table, session_get_tuple(sess));
          break;
     case SESSION_TYPE_UDP:
          SESSION_LOG_DEBUG("evicte udp old session: %lu", session_get_id(sess));
          mgr->stat.udp_sess.nr_old_sess_evicted++;
          session_table_del(mgr->udp_sess_table, session_get_tuple(sess));
          evicted_session_filter_add(mgr->evicte_sess_filter, session_get_tuple(sess), now);
          break;
     default:
          assert(0);
          break;
     }
}

static struct session *session_manager_new_tcp_session(struct session_manager *mgr, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     const struct pkt_layer *tcp_layer = packet_get_innermost_layer(pkt, LAYER_TYPE_TCP);
     const struct tcphdr *hdr = (const struct tcphdr *)tcp_layer->hdr_ptr;
     uint8_t flags = tcp_hdr_get_flags(hdr);
     if (!(flags & TH_SYN))
     {
          return NULL;
     }

     // tcp table full evict old session
     if (mgr->tcp_overload_evict_old_sess && mgr->stat.tcp_sess.nr_sess_used >= mgr->max_tcp_session_num - EVICTE_SESSION_BURST)
     {
          struct session *evic_sess = session_table_find_lru(mgr->tcp_sess_table);
          session_manager_evicte_session(mgr, evic_sess, now);
     }

     enum session_dir dir = (flags & TH_ACK) ? SESSION_DIR_S2C : SESSION_DIR_C2S;
     struct session *sess = session_pool_pop(mgr->sess_pool);
     if (sess == NULL)
     {
          assert(0);
          return NULL;
     }
     session_init(sess);
     session_set_id(sess, id_generator_alloc());

     if (tcp_pcb_init(&sess->tcp_pcb, mgr->tcp_reassembly_max_timeout, mgr->tcp_reassembly_max_segments) == -1)
     {
          assert(0);
          session_pool_push(mgr->sess_pool, sess);
          return NULL;
     }
     tcp_pcb_update(&sess->tcp_pcb, dir, tcp_layer, now);

     enum session_state next_state = session_transition_run(SESSION_STATE_INIT, TCP_SYN);
     session_update(sess, next_state, pkt, key, dir, now);
     session_transition_log(sess, SESSION_STATE_INIT, next_state, TCP_SYN);
     session_stat_inc(&mgr->stat.tcp_sess, next_state);

     uint64_t timeout = (flags & TH_ACK) ? mgr->tcp_handshake_timeout : mgr->tcp_init_timeout;
     session_timer_update(mgr->sess_timer, sess, now + timeout);
     session_table_add(mgr->tcp_sess_table, key, sess);

     duplicated_packet_filter_add(mgr->dup_pkt_filter, pkt, now);
     mgr->stat.tcp_sess.nr_sess_used++;

     return sess;
}

static struct session *session_manager_new_udp_session(struct session_manager *mgr, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     // udp table full evict old session
     if (mgr->udp_overload_evict_old_sess && mgr->stat.udp_sess.nr_sess_used >= mgr->max_udp_session_num - EVICTE_SESSION_BURST)
     {
          struct session *evic_sess = session_table_find_lru(mgr->udp_sess_table);
          session_manager_evicte_session(mgr, evic_sess, now);
     }

     struct session *sess = session_pool_pop(mgr->sess_pool);
     if (sess == NULL)
     {
          assert(sess);
          return NULL;
     }
     mgr->stat.udp_sess.nr_sess_used++;
     session_init(sess);
     session_set_id(sess, id_generator_alloc());

     enum session_dir dir = identify_direction_by_port(ntohs(key->src_port), ntohs(key->dst_port));
     enum session_state next_state = session_transition_run(SESSION_STATE_INIT, UDP_DATA);
     session_update(sess, next_state, pkt, key, dir, now);
     session_transition_log(sess, SESSION_STATE_INIT, next_state, UDP_DATA);
     session_stat_inc(&mgr->stat.udp_sess, next_state);

     session_timer_update(mgr->sess_timer, sess, now + mgr->udp_data_timeout);
     session_table_add(mgr->udp_sess_table, key, sess);

     return sess;
}

static int session_manager_update_tcp_session(struct session_manager *mgr, struct session *sess, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     const struct pkt_layer *tcp_layer = packet_get_innermost_layer(pkt, LAYER_TYPE_TCP);
     const struct tcphdr *hdr = (const struct tcphdr *)tcp_layer->hdr_ptr;
     enum session_dir dir = identify_direction_by_history(sess, key);
     uint8_t flags = tcp_hdr_get_flags(hdr);
     int inputs = (flags & TH_SYN) ? TCP_SYN : NONE;
     inputs |= (flags & TH_FIN) ? TCP_FIN : NONE;
     inputs |= (flags & TH_RST) ? TCP_RST : NONE;
     inputs |= tcp_layer->pld_len ? TCP_DATA : NONE;
     enum session_state curr_state = session_get_state(sess);
     enum session_state next_state = session_transition_run(curr_state, inputs);
     session_update(sess, next_state, pkt, key, dir, now);
     session_transition_log(sess, curr_state, next_state, inputs);
     session_stat_update(mgr, sess, curr_state, next_state);

     tcp_pcb_update(&sess->tcp_pcb, dir, tcp_layer, now);

     // set closing reason
     if (next_state == SESSION_STATE_CLOSING && !session_get_closing_reason(sess))
     {
          if (tcp_hdr_get_fin_flag(hdr))
          {
               session_set_closing_reason(sess, (dir == SESSION_DIR_C2S ? CLOSING_BY_CLIENT_FIN : CLOSING_BY_SERVER_FIN));
          }
          if (tcp_hdr_get_rst_flag(hdr))
          {
               session_set_closing_reason(sess, (dir == SESSION_DIR_C2S ? CLOSING_BY_CLIENT_RST : CLOSING_BY_SERVER_RST));
          }
     }

     uint16_t sub_state = sess->tcp_pcb.sub_state;

     uint64_t timeout = 0;
     switch (next_state)
     {
     case SESSION_STATE_OPENING:
          if (flags & TH_SYN)
          {
               timeout = (flags & TH_ACK) ? mgr->tcp_handshake_timeout : mgr->tcp_init_timeout;
          }
          else
          {
               timeout = mgr->tcp_data_timeout;
          }
          break;
     case SESSION_STATE_ACTIVE:
          timeout = mgr->tcp_data_timeout;
          break;
     case SESSION_STATE_CLOSING:
          if (flags & TH_FIN)
          {
               timeout = (sub_state & TCP_C2S_FIN_RCVD && sub_state & TCP_S2C_FIN_RCVD) ? mgr->tcp_time_wait_timeout : mgr->tcp_half_closed_timeout;
          }
          else if (flags & TH_RST)
          {
               timeout = (sub_state & TCP_C2S_RST_RCVD || sub_state & TCP_S2C_RST_RCVD) ? mgr->tcp_time_wait_timeout : mgr->tcp_unverified_rst_timeout;
          }
          else
          {
               timeout = mgr->tcp_data_timeout;
          }
          break;
     case SESSION_STATE_DISCARD:
          timeout = mgr->tcp_discard_timeout;
          break;
     default:
          assert(0);
          break;
     }
     session_timer_update(mgr->sess_timer, sess, now + timeout);

     return 0;
}

static int session_manager_update_udp_session(struct session_manager *mgr, struct session *sess, const struct packet *pkt, const struct tuple6 *key, uint64_t now)
{
     enum session_dir dir = identify_direction_by_history(sess, key);
     enum session_state curr_state = session_get_state(sess);
     enum session_state next_state = session_transition_run(curr_state, UDP_DATA);
     session_update(sess, next_state, pkt, key, dir, now);
     session_transition_log(sess, curr_state, next_state, UDP_DATA);
     session_stat_update(mgr, sess, curr_state, next_state);
     session_timer_update(mgr->sess_timer, sess, now + mgr->udp_data_timeout);

     return 0;
}

/******************************************************************************
 * Public API
 ******************************************************************************/

struct session_manager *session_manager_new(struct session_manager_options *opts, uint64_t now)
{
     if (check_options(opts) == -1)
     {
          return NULL;
     }

     struct session_manager *mgr = (struct session_manager *)calloc(1, sizeof(struct session_manager));
     if (mgr == NULL)
     {
          return NULL;
     }
     // max session number
     mgr->max_tcp_session_num = (opts->max_tcp_session_num < EVICTE_SESSION_BURST * 2) ? EVICTE_SESSION_BURST * 2 : opts->max_tcp_session_num;
     mgr->max_udp_session_num = (opts->max_udp_session_num < EVICTE_SESSION_BURST * 2) ? EVICTE_SESSION_BURST * 2 : opts->max_udp_session_num;
     // session overload
     mgr->stat.tcp_sess.nr_sess_init = 0;
     mgr->tcp_overload_evict_old_sess = opts->tcp_overload_evict_old_sess;
     mgr->udp_overload_evict_old_sess = opts->udp_overload_evict_old_sess;
     // session timeout
     mgr->tcp_init_timeout = opts->tcp_init_timeout;
     mgr->tcp_handshake_timeout = opts->tcp_handshake_timeout;
     mgr->tcp_data_timeout = opts->tcp_data_timeout;
     mgr->tcp_half_closed_timeout = opts->tcp_half_closed_timeout;
     mgr->tcp_time_wait_timeout = opts->tcp_time_wait_timeout;
     mgr->tcp_discard_timeout = opts->tcp_discard_timeout;
     mgr->tcp_unverified_rst_timeout = opts->tcp_unverified_rst_timeout;
     mgr->udp_data_timeout = opts->udp_data_timeout;

     // tcp reassembly
     mgr->tcp_reassembly_max_timeout = opts->tcp_reassembly_max_timeout;
     mgr->tcp_reassembly_max_segments = opts->tcp_reassembly_max_segments;
     // duplicated packet filter
     struct duplicated_packet_filter_options duplicated_packet_filter_opts = {
         .enable = opts->duplicated_packet_filter_enable,
         .capacity = opts->duplicated_packet_filter_capacity,
         .timeout = opts->duplicated_packet_filter_timeout,
         .error_rate = opts->duplicated_packet_filter_error_rate,
     };
     // evicted session filter
     struct evicted_session_filter_options evicted_session_filter_opts = {
         .enable = opts->evicted_session_filter_enable,
         .capacity = opts->evicted_session_filter_capacity,
         .timeout = opts->evicted_session_filter_timeout,
         .error_rate = opts->evicted_session_filter_error_rate,
     };

     mgr->sess_pool = session_pool_new(mgr->max_tcp_session_num + mgr->max_udp_session_num);
     mgr->tcp_sess_table = session_table_new();
     mgr->udp_sess_table = session_table_new();
     mgr->sess_timer = session_timer_new(now);
     mgr->dup_pkt_filter = duplicated_packet_filter_new(&duplicated_packet_filter_opts, now);
     mgr->evicte_sess_filter = evicted_session_filter_new(&evicted_session_filter_opts, now);
     if (mgr->sess_pool == NULL || mgr->tcp_sess_table == NULL || mgr->udp_sess_table == NULL || mgr->sess_timer == NULL || mgr->dup_pkt_filter == NULL || mgr->evicte_sess_filter == NULL)
     {
          goto error;
     }

     INIT_LIST_HEAD(&mgr->evicte_queue);
     session_filter_init();
     session_transition_init();

     return mgr;

error:
     session_manager_free(mgr);
     return NULL;
}

void session_manager_free(struct session_manager *mgr)
{
     struct session *sess;
     if (mgr)
     {
          // free all evicted session
          while (!list_empty(&mgr->evicte_queue))
          {
               sess = list_first_entry(&mgr->evicte_queue, struct session, evicte);
               list_del(&sess->evicte);
               session_manager_free_session(mgr, sess);
          }
          // free all udp session
          while (mgr->udp_sess_table && (sess = session_table_find_lru(mgr->udp_sess_table)))
          {
               session_manager_free_session(mgr, sess);
          }
          // free all tcp session
          while (mgr->tcp_sess_table && (sess = session_table_find_lru(mgr->tcp_sess_table)))
          {
               session_manager_free_session(mgr, sess);
          }
          evicted_session_filter_free(mgr->evicte_sess_filter);
          duplicated_packet_filter_free(mgr->dup_pkt_filter);
          session_timer_free(mgr->sess_timer);
          session_table_free(mgr->udp_sess_table);
          session_table_free(mgr->tcp_sess_table);
          session_pool_free(mgr->sess_pool);
          free(mgr);
          mgr = NULL;
     }
}

struct session *session_manager_new_session(struct session_manager *mgr, const struct packet *pkt, uint64_t now)
{
     struct tuple6 key;
     if (packet_get_innermost_tuple6(pkt, &key))
     {
          return NULL;
     }
     if (session_filter_run(mgr, FILTER_STAGE_PRE_NEW_SESS, NULL, pkt, &key, now))
     {
          return NULL;
     }
     switch (key.ip_proto)
     {
     case IPPROTO_TCP:
          return session_manager_new_tcp_session(mgr, pkt, &key, now);
     case IPPROTO_UDP:
          return session_manager_new_udp_session(mgr, pkt, &key, now);
     default:
          return NULL;
     }
}

void session_manager_free_session(struct session_manager *mgr, struct session *sess)
{
     if (sess)
     {
          SESSION_LOG_DEBUG("session %lu closed (%s)", session_get_id(sess), closing_reason_to_str(session_get_closing_reason(sess)));

          session_timer_del(mgr->sess_timer, sess);
          switch (session_get_type(sess))
          {
          case SESSION_TYPE_TCP:
               tcp_pcb_clean(&sess->tcp_pcb);
               session_table_del(mgr->tcp_sess_table, session_get_tuple(sess));
               session_stat_dec(&mgr->stat.tcp_sess, session_get_state(sess));
               mgr->stat.tcp_sess.nr_sess_used--;
               break;
          case SESSION_TYPE_UDP:
               session_table_del(mgr->udp_sess_table, session_get_tuple(sess));
               session_stat_dec(&mgr->stat.udp_sess, session_get_state(sess));
               mgr->stat.udp_sess.nr_sess_used--;
               break;
          default:
               assert(0);
               break;
          }
          session_clean_packet(sess, SESSION_PACKET_C2S_1ST);
          session_clean_packet(sess, SESSION_PACKET_S2C_1ST);
          session_clean_packet(sess, SESSION_PACKET_CURRENT);
          session_set_cur_dir(sess, SESSION_DIR_NONE);
          session_free_all_ex_data(sess);
          session_pool_push(mgr->sess_pool, sess);
          sess = NULL;
     }
}

struct session *session_manager_lookup_session(struct session_manager *mgr, const struct packet *pkt)
{
     struct tuple6 key;
     if (packet_get_innermost_tuple6(pkt, &key))
     {
          return NULL;
     }
     switch (key.ip_proto)
     {
     case IPPROTO_UDP:
          return session_table_find_tuple(mgr->udp_sess_table, &key);
     case IPPROTO_TCP:
          return session_table_find_tuple(mgr->tcp_sess_table, &key);
     default:
          return NULL;
     }
}

int session_manager_update_session(struct session_manager *mgr, struct session *sess, const struct packet *pkt, uint64_t now)
{
     struct tuple6 key;
     if (packet_get_innermost_tuple6(pkt, &key))
     {
          return -1;
     }
     if (session_filter_run(mgr, FILTER_STAGE_PRE_UPDATE_SESS, sess, pkt, &key, now))
     {
          return -1;
     }
     switch (session_get_type(sess))
     {
     case SESSION_TYPE_TCP:
          return session_manager_update_tcp_session(mgr, sess, pkt, &key, now);
     case SESSION_TYPE_UDP:
          return session_manager_update_udp_session(mgr, sess, pkt, &key, now);
     default:
          return -1;
     }
}

struct session *session_manager_get_expired_session(struct session_manager *mgr, uint64_t now)
{
     struct session *sess = session_timer_expire(mgr->sess_timer, now);
     if (sess)
     {
          enum session_state curr_state = session_get_state(sess);
          enum session_state next_state = session_transition_run(curr_state, TIMEOUT);
          session_transition_log(sess, curr_state, next_state, TIMEOUT);
          session_set_state(sess, next_state);
          session_stat_update(mgr, sess, curr_state, next_state);

          if (next_state == SESSION_STATE_CLOSED)
          {
               // need free session
               if (!session_get_closing_reason(sess))
               {
                    session_set_closing_reason(sess, CLOSING_BY_TIMEOUT);
               }
               return sess;
          }
          else
          {
               // in closing state, only update timeout
               uint64_t timeout = 0;
               switch (session_get_type(sess))
               {
               case SESSION_TYPE_TCP:
                    timeout = mgr->tcp_data_timeout;
                    break;
               case SESSION_TYPE_UDP:
                    timeout = mgr->udp_data_timeout;
                    break;
               default:
                    assert(0);
                    break;
               }
               session_timer_update(mgr->sess_timer, sess, now + timeout);
               return NULL;
          }
     }

     return NULL;
}

struct session *session_manager_get_evicted_session(struct session_manager *mgr)
{
     if (list_empty(&mgr->evicte_queue))
     {
          return NULL;
     }
     else
     {
          struct session *sess = list_first_entry(&mgr->evicte_queue, struct session, evicte);
          list_del(&sess->evicte);
          return sess;
     }
}

uint64_t session_manager_get_expire_interval(struct session_manager *mgr)
{
     return session_timer_next_expire_interval(mgr->sess_timer);
}

void session_manager_print_stat(struct session_manager *mgr)
{
     if (mgr)
     {
          SESSION_LOG_DEBUG("session_manager_stat->tcp_sess_num: used: %u, init: %u, opening: %u, active: %u, closing: %u, closed: %u, evic_new: %u, evic_old: %u",
                            mgr->stat.tcp_sess.nr_sess_used, mgr->stat.tcp_sess.nr_sess_init, mgr->stat.tcp_sess.nr_sess_opening,
                            mgr->stat.tcp_sess.nr_sess_active, mgr->stat.tcp_sess.nr_sess_closing, mgr->stat.tcp_sess.nr_sess_closed,
                            mgr->stat.tcp_sess.nr_new_sess_evicted, mgr->stat.tcp_sess.nr_old_sess_evicted);
          SESSION_LOG_DEBUG("session_manager_stat->udp_sess_num: used: %u, init: %u, opening: %u, active: %u, closing: %u, closed: %u, evic_new: %u, evic_old: %u",
                            mgr->stat.udp_sess.nr_sess_used, mgr->stat.udp_sess.nr_sess_init, mgr->stat.udp_sess.nr_sess_opening,
                            mgr->stat.udp_sess.nr_sess_active, mgr->stat.udp_sess.nr_sess_closing, mgr->stat.udp_sess.nr_sess_closed,
                            mgr->stat.udp_sess.nr_new_sess_evicted, mgr->stat.udp_sess.nr_old_sess_evicted);
          SESSION_LOG_DEBUG("session_manager_stat: dup_pkts: %u, dup_bytes: %u, evic_pkts: %u, evic_bytes: %u",
                            mgr->stat.dup_pkt.nr_pkts, mgr->stat.dup_pkt.nr_bytes,
                            mgr->stat.evc_pkt.nr_pkts, mgr->stat.evc_pkt.nr_bytes);
     }
}

struct session_manager_stat *session_manager_get_stat(struct session_manager *mgr)
{
     return &mgr->stat;
}