/*
 * This file Copyright (C) 2015 Mnemosyne LLC
 *
 * It may be used under the GNU GPL versions 2 or 3
 * or any future license endorsed by Mnemosyne LLC.
 *
 * $Id$
 */

#include <assert.h>
#include <errno.h>
#include <pthread.h>
#include <signal.h>
#include <stdlib.h> /* daemon (), exit () */
#include <fcntl.h> /* open () */
#include <unistd.h> /* fork (), setsid (), chdir (), dup2 (), close (), pipe () */

#include <libtransmission/transmission.h>
#include <libtransmission/error.h>
#include <libtransmission/utils.h>

#include "daemon.h"

/***
****
***/

static const dtr_callbacks * callbacks = NULL;
static void * callback_arg = NULL;

static int signal_pipe[2];

/***
****
***/

static void
set_system_error (tr_error   ** error,
                  int           code,
                  const char  * message)
{
  tr_error_set (error, code, "%s (%d): %s", message, code, tr_strerror (code));
}

/***
****
***/

static void
handle_signal (int sig)
{
  switch (sig)
    {
      case SIGHUP:
        callbacks->on_reconfigure (callback_arg);
        break;

      case SIGINT:
      case SIGTERM:
        callbacks->on_stop (callback_arg);
        break;

      default:
        assert (!"Unexpected signal");
    }
}

static void
send_signal_to_pipe (int sig)
{
  const int old_errno = errno;

  write (signal_pipe[1], &sig, sizeof (sig));

  errno = old_errno;
}

static void *
signal_handler_thread_main (void * arg UNUSED)
{
  int sig;

  while (read (signal_pipe[0], &sig, sizeof (sig)) == sizeof (sig) && sig != 0)
    handle_signal (sig);

  return NULL;
}

static bool
create_signal_pipe (tr_error ** error)
{
  if (pipe (signal_pipe) == -1)
    {
      set_system_error (error, errno, "pipe() failed");
      return false;
    }

  return true;
}

static void
destroy_signal_pipe ()
{
  close (signal_pipe[0]);
  close (signal_pipe[1]);
}

static bool
create_signal_handler_thread (pthread_t  * thread,
                              tr_error  ** error)
{
  if (!create_signal_pipe (error))
    return false;

  if ((errno = pthread_create (thread, NULL, &signal_handler_thread_main, NULL)) != 0)
    {
      set_system_error (error, errno, "pthread_create() failed");
      destroy_signal_pipe ();
      return false;
    }

  return true;
}

static void
destroy_signal_handler_thread (pthread_t thread)
{
  send_signal_to_pipe (0);
  pthread_join (thread, NULL);

  destroy_signal_pipe ();
}

static bool
setup_signal_handler (int         sig,
                      tr_error ** error)
{
  assert (sig != 0);

  if (signal (sig, &send_signal_to_pipe) == SIG_ERR)
    {
      set_system_error (error, errno, "signal() failed");
      return false;
    }

  return true;
}

/***
****
***/

bool
dtr_daemon (const dtr_callbacks  * cb,
            void                 * cb_arg,
            bool                   foreground,
            int                  * exit_code,
            tr_error            ** error)
{
  callbacks = cb;
  callback_arg = cb_arg;

  *exit_code = 1;

  if (!foreground)
    {

#if defined (HAVE_DAEMON) && !defined (__UCLIBC__)

      if (daemon (true, false) == -1)
        {
          set_system_error (error, errno, "daemon() failed");
          return false;
        }

#else

      /* this is loosely based off of glibc's daemon () implementation
       * http://sourceware.org/git/?p=glibc.git;a=blob_plain;f=misc/daemon.c */

      switch (fork ())
        {
          case -1:
            set_system_error (error, errno, "fork() failed");
            return false;
          case 0:
            break;
          default:
            *exit_code = 0;
            return true;
        }

      if (setsid () == -1)
        {
          set_system_error (error, errno, "setsid() failed");
          return false;
        }

      /*
      if (chdir ("/") == -1)
        {
          set_system_error (error, errno, "chdir() failed");
          return false;
        }
      */

      {
        const int fd = open ("/dev/null", O_RDWR, 0);
        dup2 (fd, STDIN_FILENO);
        dup2 (fd, STDOUT_FILENO);
        dup2 (fd, STDERR_FILENO);
        close (fd);
      }

#endif

    }

  pthread_t signal_thread;
  if (!create_signal_handler_thread (&signal_thread, error))
    return false;

  if (!setup_signal_handler (SIGINT, error) ||
      !setup_signal_handler (SIGTERM, error) ||
      !setup_signal_handler (SIGHUP, error))
    {
      destroy_signal_handler_thread (signal_thread);
      return false;
    }

  *exit_code = cb->on_start (cb_arg, foreground);

  destroy_signal_handler_thread (signal_thread);

  return true;
}