/*
 * This program listens for results sent by OwlPS Positioning on a UDP
 * socket, and listens for a client on a TCP socket. The client is
 * expected to send an HTTP GET request, with the request string as the
 * first variable value (the variable name does not matter).
 * For example, a correct request is detected if you load
 *   http://localhost:8080/?request=ReadSimpleResults
 * (assuming the host running this program is localhost).
 *
 * The UDP listening port is the port on which OwlPS Positioning sends
 * result by default.
 * The TCP listening port is 8080.
 *
 * Only the last result read from the positioning server, for each
 * mobile, is memorised and provided to the HTTP client.
 *
 * The HTTP requests currently implemented are listed bellow.
 *
 * ** Request "ReadResults" **
 * Answer in case of error:
 *   Results;NOK;Explanation
 * Normal answer:
 *   Results;OK;Nb_results;Result_1;…;Result_n
 * Nb_results is the number of results in the answer (number of mobiles).
 * Result_i follows this format:
 *   Mobile_MAC;Request_type;Request_timestamp;Nb_algo;Algo_1;…;Algo_n
 * Nb_algo is the number of algorithms in the result.
 * Algo_i follows this format:
 *   Algorithm_name;X;Y;Z;Error;Area_name
 * Error is the distance from the true coordinates of the mobile, if
 * known; if unknown, Error is set to -1.
 * Area_name is the name of the area or room in which the mobile is (may
 * be empty).
 *
 * ** Unknown request **
 * If a unknown request is received, the answer format is:
 *   UnknownRequest;NOK
 *
 * ** Request "ReadSimpleResults" **
 * Answer in case of error:
 *   SimpleResults;NOK;Explanation
 * Normal answer:
 *   SimpleResults;OK;Nb_results;Result_1;…;Result_n
 * Nb_results is the number of results in the answer (number of mobiles).
 * Result_i follows this format:
 *   Mobile_MAC;X;Y;Z;Area_name
 * Area_name is the name of the area or room in which the mobile is (may
 * be empty).
 */

#include "owlps-udp-to-http.h"

#include <signal.h>
#include <semaphore.h>
#include <pthread.h>
#include <unistd.h>
#include <stdlib.h>
#include <strings.h>
#include <string.h>

#include <assert.h>


char *program_name = NULL ;

results_list *results = NULL ;
unsigned int nb_results = 0 ;
sem_t lock_results ;

int udp_sockfd = -1 ;
int tcp_sockfd = -1 ;

char *answer = NULL ; // Answer to send to the client
size_t answer_strlen = 0 ; // Total size of the answer string
size_t answer_buflen = 0 ; // Size of the answer allocated buffer


int main(int argc, char *argv[])
{
  struct sigaction action ; // Signal handler structure
  int ret = 0 ; // Program return value
  pthread_t tcp_server_thread ;

  program_name = argv[0] ;
  owl_run = owl_true ;

  if (argc > 1)
    fprintf(stderr,
            "Sorry, this program does not take any argument yet.\n") ;

  /* Set up signal handlers */
  action.sa_flags = 0 ;
  sigemptyset(&action.sa_mask) ;
  action.sa_handler = owl_sigint_handler ;
  sigaction(SIGINT, &action, NULL) ;
  action.sa_handler = owl_sigterm_handler ;
  sigaction(SIGTERM, &action, NULL) ;

  /* Set up the semaphore */
  sem_init(&lock_results, 0, 1) ;

  /* Prepare the TCP socket */
  ret = init_tcp_socket() ;
  if (ret)
    goto exit ;

  /* Launch the TCP thread */
  ret = pthread_create(&tcp_server_thread, NULL,
                       &tcp_server, NULL) ;
  if (ret)
    {
      perror("Cannot create the TCP server thread") ;
      ret = 1 ;
      goto exit ;
    }

  /* Main loop */
  ret = receive_udp() ;

  /* Stop the TCP thread */
  // We must cancel the thread because it can be blocked on the
  // recv() call:
  if (pthread_cancel(tcp_server_thread))
    perror("Cannot cancel the TCP server thread") ;
  if (pthread_join(tcp_server_thread, NULL))
    perror("Cannot join the TCP server thread") ;

 exit:
  /* Close sockets */
  if (tcp_sockfd >= 0)
    if (close(tcp_sockfd))
      perror("Error closing the TCP socket") ;
  if (udp_sockfd >= 0)
    if (close(udp_sockfd))
      perror("Error closing the UDP socket") ;

  /* Last cleaning */
  free(answer) ;
  free_results_list() ;
  sem_destroy(&lock_results) ;

  printf("%s: end.\n", program_name) ;
  return ret ;
}


/*
 * Opens the UDP socket and reads from it the results sent by OwlPS
 * Positioning.
 * Returns a non-zero value in case of error.
 */
int receive_udp()
{
  owl_result *result ;

  /* Open the UDP socket */
  udp_sockfd = owl_create_udp_listening_socket(OWL_DEFAULT_RESULT_PORT) ;
  if (udp_sockfd < 0)
    return 1 ;

  /* UDP read loop */
  while (owl_run)
    {
      result = owl_receive_position(udp_sockfd) ;
      if (result == NULL)
        return 1 ;
      owl_print_result(result) ;
      store_result(result) ;
      printf("--------------\n") ;
    }

  return 0 ;
}


/*
 * Adds a new owl_result to the results' list.
 */
void store_result(owl_result *new_result)
{
  sem_wait(&lock_results) ;

  // The results' list does not exist yet
  if (! results)
    {
      results = malloc(sizeof(results_list)) ;
      ++nb_results ;
      results->result = new_result ;
      results->next = NULL ;
    }

  // The results' list contains at least 1 element
  else
    {
      // Search for an existing result with the same mobile's MAC
      results_list *res = results ;
      while (res != NULL)
        {
          char *mac = res->result->mobile_mac_addr ;
          if (strncmp(mac, new_result->mobile_mac_addr,
                      OWL_ETHER_ADDR_STRLEN) == 0)
            break ;
          res = res->next ;
        }

      if (res == NULL) // Not found, adding an element
        {
          res = malloc(sizeof(results_list)) ;
          ++nb_results ;
          res->next = results ;
          results = res ;
        }
      else // Found, clearing it
        owl_free_result(res->result) ;

      res->result = new_result ;
    }

  sem_post(&lock_results) ;
}


/*
 * Opens the TCP socket.
 * Returns a non-zero value in case of error.
 */
int init_tcp_socket()
{
  struct sockaddr_in server_addr ;

  tcp_sockfd = socket(AF_INET, SOCK_STREAM, 0) ;
  if (tcp_sockfd < 0)
    {
      perror("Error opening the TCP socket") ;
      return tcp_sockfd ;
    }

  bzero((char *) &server_addr, sizeof(server_addr)) ;
  server_addr.sin_family = AF_INET ;
  server_addr.sin_addr.s_addr = INADDR_ANY ;
  server_addr.sin_port = htons(TCP_PORT) ;


  if (bind(tcp_sockfd, (struct sockaddr *) &server_addr,
           sizeof(server_addr)) < 0)
    {
      perror("Error binding the TCP socket") ;
      return -1 ;
    }

  return 0 ;
}


/*
 * Waits for requests from HTTP clients.
 */
void* tcp_server(void *NULL_value)
{
  int newsockfd ;
  socklen_t client_len ;
  struct sockaddr_in client_addr ;
  ssize_t nbytes ; // recv/send return value
  char client_message[CLIENT_MESSAGE_STRLEN] ;
  char client_request[CLIENT_REQUEST_STRLEN] ;
  int request_id ;

  listen(tcp_sockfd, NB_CONNECTIONS) ;
  client_len = sizeof(client_addr) ;

  // Prepare the answer, assuming there is only 1 full result (an error
  // message will also fit)
  answer_buflen = ANSWER_HDR_STRLEN + OWL_CSV_RESULT_STRLEN ;
  answer = malloc(answer_buflen) ;
  strncpy(answer, ANSWER_HDR, ANSWER_HDR_STRLEN) ;

  while (owl_run)
    {
      newsockfd = accept(tcp_sockfd,
                         (struct sockaddr*) &client_addr, &client_len) ;
      if (newsockfd < 0)
        {
          perror("Error accepting a connection on the TCP socket") ;
          continue ;
        }

      nbytes =
        recv(newsockfd, client_message, CLIENT_MESSAGE_STRLEN, 0) ;
      if (nbytes < 0)
        {
          perror("Error reading from the TCP socket") ;
          close(newsockfd) ;
          continue ;
        }
      client_message[nbytes] = '\0' ;

#ifdef DEBUG
      printf("Got a message from the client:\n"
             "\"%s\"\n", client_message) ;
#endif // DEBUG

      request_id =
        extract_request_from_message(client_request, client_message) ;
      prepare_answer(request_id) ;

#ifdef DEBUG
      printf("Answer to send:\n\"%s\"\n", answer) ;
#endif // DEBUG

      /* Send the answer */
      nbytes = send(newsockfd, answer, answer_strlen, 0) ;
      if (nbytes < 0)
        perror("Error sending answer to the TCP socket") ;

      close(newsockfd) ;
    }

  pthread_exit(NULL_value) ;
}


int
extract_request_from_message(char client_request[CLIENT_REQUEST_STRLEN],
                             char *client_message)
{
  char *token ;

  token = strchr(client_message, '=') ;
  if (! token)
    return 0 ;
  ++token ;
  token = strsep(&token, " ") ;

  if (strncmp(SIMPLE_RESULTS_REQUEST, token,
              strlen(SIMPLE_RESULTS_REQUEST)) == 0)
    {
      strncpy(client_request, SIMPLE_RESULTS_REQUEST,
              CLIENT_REQUEST_STRLEN) ;
      return SIMPLE_RESULTS_ID ;
    }

  if (strncmp(RESULTS_REQUEST, token,
              strlen(RESULTS_REQUEST)) == 0)
    {
      strncpy(client_request, RESULTS_REQUEST,
              CLIENT_REQUEST_STRLEN) ;
      return RESULTS_ID ;
    }

  return 0 ; // No known request found
}


/*
 * Prepare the answer string to send to the TCP client.
 */
void prepare_answer(int request_id)
{
  // Reset the answer's length:
  answer_strlen = ANSWER_HDR_STRLEN ;

  switch (request_id)
    {
    case RESULTS_ID:
      strncpy(answer + answer_strlen, RESULTS_ANSWER,
              strlen(RESULTS_ANSWER)) ;
      answer_strlen += strlen(RESULTS_ANSWER) ;

      sem_wait(&lock_results) ;

      if (! results)
        {
          char answer_end[] = ";NOK;NoResult" ;
          strncpy(answer + answer_strlen, answer_end,
                  strlen(answer_end)) ;
          answer_strlen += strlen(answer_end) ;
        }

      else
        {
          results_list *result ;
          char answer_begin[10] ;
          size_t answer_begin_len ;

          snprintf(answer_begin, 10, ";OK;%u", nb_results) ;
          answer_begin_len = strlen(answer_begin) ;
          strncpy(answer + answer_strlen, answer_begin,
                  answer_begin_len) ;
          answer_strlen += answer_begin_len ;

          realloc_answer(answer_strlen +
                         nb_results * OWL_CSV_RESULT_STRLEN) ;

          result = results ;
          while (result != NULL)
            {
              char result_str[OWL_CSV_RESULT_STRLEN] ;
              size_t result_len ;
              owl_result_to_csv(result_str, result->result) ;
              result_len = strlen(result_str) ;
              answer[answer_strlen++] = ';' ;
              assert(answer_strlen<answer_buflen) ;
              strncpy(answer + answer_strlen, result_str,
                      result_len) ;
              answer_strlen += result_len ;
              result = result->next ;
            }
        }

      sem_post(&lock_results) ;

      break ;

    case SIMPLE_RESULTS_ID:
      strncpy(answer + answer_strlen, SIMPLE_RESULTS_ANSWER,
              strlen(SIMPLE_RESULTS_ANSWER)) ;
      answer_strlen += strlen(SIMPLE_RESULTS_ANSWER) ;

      sem_wait(&lock_results) ;

      if (! results)
        {
          char answer_end[] = ";NOK;NoResult" ;
          strncpy(answer + answer_strlen, answer_end,
                  strlen(answer_end)) ;
          answer_strlen += strlen(answer_end) ;
        }

      else
        {
          results_list *result ;
          char answer_begin[10] ;
          size_t answer_begin_len ;

          snprintf(answer_begin, 10, ";OK;%u", nb_results) ;
          answer_begin_len = strlen(answer_begin) ;
          strncpy(answer + answer_strlen, answer_begin,
                  answer_begin_len) ;
          answer_strlen += answer_begin_len ;

          realloc_answer(answer_strlen +
                         nb_results * OWL_CSV_RESULT_SIMPLE_STRLEN) ;

          result = results ;
          while (result != NULL)
            {
              char result_str[OWL_CSV_RESULT_SIMPLE_STRLEN] ;
              size_t result_len ;
              owl_result_to_csv_simple(result_str, result->result) ;
              result_len = strlen(result_str) ;
              answer[answer_strlen++] = ';' ;
              strncpy(answer + answer_strlen, result_str,
                      result_len) ;
              answer_strlen += result_len ;
              result = result->next ;
            }
        }

      sem_post(&lock_results) ;

      break ;

    default:
      {
        char answer_end[] = "UnknownRequest;NOK" ;
        strncpy(answer + ANSWER_HDR_STRLEN, answer_end,
                strlen(answer_end)) ;
        answer_strlen += strlen(answer_end) ;
      }
    }

  answer[answer_strlen] = '\0' ;
}


/*
 * Realloc the answer buffer to the if needed: grows it if new_size is
 * greater than the current size, shrink it if the current size is
 * greater than the double of new_size.
 */
void realloc_answer(size_t new_size)
{
  if (new_size > answer_buflen)
    answer_buflen = new_size ;
  else if (answer_buflen / 2 >= new_size)
    answer_buflen /= 2 ;
  else
    return ;

  answer = realloc(answer, answer_buflen) ;
}


/*
 * Frees the memory allocated for the results' list.
 */
void free_results_list()
{
  results_list *tmp_res ;
  while (results != NULL)
    {
      owl_free_result(results->result) ;
      tmp_res = results ;
      results = results->next ;
      free(tmp_res) ;
    }
  nb_results = 0 ;
}