/*
 * This file Copyright (C) 2016 Mnemosyne LLC
 *
 * It may be used under the GNU GPL versions 2 or 3
 * or any future license endorsed by Mnemosyne LLC.
 *
 */

#include <string.h>
#include <time.h>

#ifndef _WIN32
 #include <sys/stat.h>
#endif

#include "transmission.h"
#include "crypto-utils.h"
#include "error.h"
#include "error-types.h"
#include "file.h"
#include "log.h"
#include "platform.h"
#include "session-id.h"
#include "utils.h"

#define SESSION_ID_SIZE         48
#define SESSION_ID_DURATION_SEC (60 * 60) /* expire in an hour */

struct tr_session_id
{
  char          * current_value;
  char          * previous_value;
  tr_sys_file_t   current_lock_file;
  tr_sys_file_t   previous_lock_file;
  time_t          expires_at;
};

static char *
generate_new_session_id_value (void)
{
  const char   pool[] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
  const size_t pool_size = sizeof (pool) - 1;

  char * buf = tr_new (char, SESSION_ID_SIZE + 1);

  tr_rand_buffer (buf, SESSION_ID_SIZE);
  for (size_t i = 0; i < SESSION_ID_SIZE; ++i)
    buf[i] = pool[(unsigned char) buf[i] % pool_size];
  buf[SESSION_ID_SIZE] = '\0';

  return buf;
}

static char *
get_session_id_lock_file_path (const char * session_id)
{
  char * lock_file_dir = tr_getSessionIdDir ();
  char * lock_file_path = tr_strdup_printf ("%s/tr_session_id_%s", lock_file_dir, session_id);
  tr_free (lock_file_dir);
  return lock_file_path;
}

static tr_sys_file_t
create_session_id_lock_file (const char * session_id)
{
  if (session_id == NULL)
    return TR_BAD_SYS_FILE;

  char          * lock_file_path = get_session_id_lock_file_path (session_id);
  tr_sys_file_t   lock_file;
  tr_error      * error = NULL;

  lock_file = tr_sys_file_open (lock_file_path, TR_SYS_FILE_READ | TR_SYS_FILE_WRITE | TR_SYS_FILE_CREATE, 0600, &error);

  if (lock_file != TR_BAD_SYS_FILE)
    {
      if (tr_sys_file_lock (lock_file, TR_SYS_FILE_LOCK_EX | TR_SYS_FILE_LOCK_NB, &error))
        {
#ifndef _WIN32
          /* Allow any user to lock the file regardless of current umask */
          fchmod (lock_file, 0644);
#endif
        }
      else
        {
          tr_sys_file_close (lock_file, NULL);
          lock_file = TR_BAD_SYS_FILE;
        }
    }

  if (error != NULL)
    {
      tr_logAddError ("Unable to create session lock file (%d): %s", error->code, error->message);
      tr_error_free (error);
    }

  tr_free (lock_file_path);
  return lock_file;
}

static void
destroy_session_id_lock_file (tr_sys_file_t   lock_file,
                              const char    * session_id)
{
  if (lock_file != TR_BAD_SYS_FILE)
    tr_sys_file_close (lock_file, NULL);

  if (session_id != NULL)
    {
      char * lock_file_path = get_session_id_lock_file_path (session_id);
      tr_sys_path_remove (lock_file_path, NULL);
      tr_free (lock_file_path);
    }
}

tr_session_id_t
tr_session_id_new (void)
{
  const tr_session_id_t session_id = tr_new0 (struct tr_session_id, 1);

  session_id->current_lock_file = TR_BAD_SYS_FILE;
  session_id->previous_lock_file = TR_BAD_SYS_FILE;

  return session_id;
}

void
tr_session_id_free (tr_session_id_t session_id)
{
  if (session_id == NULL)
    return;

  destroy_session_id_lock_file (session_id->previous_lock_file, session_id->previous_value);
  destroy_session_id_lock_file (session_id->current_lock_file, session_id->current_value);

  tr_free (session_id->previous_value);
  tr_free (session_id->current_value);

  tr_free (session_id);
}

const char *
tr_session_id_get_current (tr_session_id_t session_id)
{
  const time_t now = tr_time ();

  if (session_id->current_value == NULL || now >= session_id->expires_at)
    {
      destroy_session_id_lock_file (session_id->previous_lock_file, session_id->previous_value);
      tr_free (session_id->previous_value);

      session_id->previous_value = session_id->current_value;
      session_id->current_value = generate_new_session_id_value ();

      session_id->previous_lock_file = session_id->current_lock_file;
      session_id->current_lock_file = create_session_id_lock_file (session_id->current_value);

      session_id->expires_at = now + SESSION_ID_DURATION_SEC;
    }

  return session_id->current_value;
}

bool
tr_session_id_is_local (const char * session_id)
{
  bool ret = false;

  if (session_id != NULL)
    {
      char          * lock_file_path = get_session_id_lock_file_path (session_id);
      tr_sys_file_t   lock_file;
      tr_error      * error = NULL;

      lock_file = tr_sys_file_open (lock_file_path, TR_SYS_FILE_READ, 0, &error);

      if (lock_file == TR_BAD_SYS_FILE)
        {
          if (TR_ERROR_IS_ENOENT (error->code))
            tr_error_clear (&error);
        }
      else
        {
          if (!tr_sys_file_lock (lock_file, TR_SYS_FILE_LOCK_SH | TR_SYS_FILE_LOCK_NB, &error))
            {
#ifndef _WIN32
              if (error->code == EWOULDBLOCK)
#else
              if (error->code == ERROR_LOCK_VIOLATION)
#endif
                {
                  ret = true;
                  tr_error_clear (&error);
                }
            }

          tr_sys_file_close (lock_file, NULL);
        }

      if (error != NULL)
        {
          tr_logAddError ("Unable to open session lock file (%d): %s", error->code, error->message);
          tr_error_free (error);
        }

      tr_free (lock_file_path);
    }

  return ret;
}