/* GNU m4 -- A simple macro processor

   Copyright (C) 1989, 1990, 1991, 1992, 1993, 2004, 2006, 2007, 2008,
   2009, 2010 Free Software Foundation, Inc.

   This file is part of GNU M4.

   GNU M4 is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   GNU M4 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

/* Handling of path search of included files via the builtins "include"
   and "sinclude".  */

#include "m4.h"

struct includes
{
  struct includes *next;        /* next directory to search */
  const char *dir;              /* directory */
  int len;
};

typedef struct includes includes;

static includes *dir_list;              /* the list of path directories */
static includes *dir_list_end;          /* the end of same */
static int dir_max_length;              /* length of longest directory name */


void
include_init (void)
{
  dir_list = NULL;
  dir_list_end = NULL;
  dir_max_length = 0;
}

void
include_env_init (void)
{
  char *path;
  char *path_end;
  char *env_path;

  if (no_gnu_extensions)
    return;

  env_path = getenv ("M4PATH");
  if (env_path == NULL)
    return;

  env_path = xstrdup (env_path);
  path = env_path;

  do
    {
      path_end = strchr (path, ':');
      if (path_end)
        *path_end = '\0';
      add_include_directory (path);
      path = path_end + 1;
    }
  while (path_end);
  free (env_path);
}

void
add_include_directory (const char *dir)
{
  includes *incl;

  if (no_gnu_extensions)
    return;

  if (*dir == '\0')
    dir = ".";

  incl = (includes *) xmalloc (sizeof (struct includes));
  incl->next = NULL;
  incl->len = strlen (dir);
  incl->dir = xstrdup (dir);

  if (incl->len > dir_max_length) /* remember len of longest directory */
    dir_max_length = incl->len;

  if (dir_list_end == NULL)
    dir_list = incl;
  else
    dir_list_end->next = incl;
  dir_list_end = incl;

#ifdef DEBUG_INCL
  xfprintf (stderr, "add_include_directory (%s);\n", dir);
#endif
}

/* Attempt to open FILE; if it opens, verify that it is not a
   directory, and ensure it does not leak across execs.  */
static FILE *
m4_fopen (const char *file)
{
  FILE *fp = fopen (file, "r");
  if (fp)
    {
      struct stat st;
      int fd = fileno (fp);
      if (fstat (fd, &st) == 0 && S_ISDIR (st.st_mode))
        {
          fclose (fp);
          errno = EISDIR;
          return NULL;
        }
      if (set_cloexec_flag (fd, true) != 0)
        M4ERROR ((warning_status, errno,
                  "Warning: cannot protect input file across forks"));
    }
  return fp;
}

/* Search for FILE, first in `.', then according to -I options.  If
   successful, return the open file, and if RESULT is not NULL, set
   *RESULT to a malloc'd string that represents the file found with
   respect to the current working directory.  */

FILE *
m4_path_search (const char *file, char **result)
{
  FILE *fp;
  includes *incl;
  char *name;                   /* buffer for constructed name */
  int e;

  if (result)
    *result = NULL;

  /* Reject empty file.  */
  if (!*file)
    {
      errno = ENOENT;
      return NULL;
    }

  /* Look in current working directory first.  */
  fp = m4_fopen (file);
  if (fp != NULL)
    {
      if (result)
        *result = xstrdup (file);
      return fp;
    }

  /* If file not found, and filename absolute, fail.  */
  if (IS_ABSOLUTE_FILE_NAME (file) || no_gnu_extensions)
    return NULL;
  e = errno;

  for (incl = dir_list; incl != NULL; incl = incl->next)
    {
      name = file_name_concat (incl->dir, file, NULL);

#ifdef DEBUG_INCL
      xfprintf (stderr, "m4_path_search (%s) -- trying %s\n", file, name);
#endif

      fp = m4_fopen (name);
      if (fp != NULL)
        {
          if (debug_level & DEBUG_TRACE_PATH)
            DEBUG_MESSAGE2 ("path search for `%s' found `%s'", file, name);
          if (result)
            *result = name;
          else
            free (name);
          return fp;
        }
      free (name);
    }
  errno = e;
  return fp;
}

#ifdef DEBUG_INCL

static void M4_GNUC_UNUSED
include_dump (void)
{
  includes *incl;

  xfprintf (stderr, "include_dump:\n");
  for (incl = dir_list; incl != NULL; incl = incl->next)
    xfprintf (stderr, "\t%s\n", incl->dir);
}

#endif /* DEBUG_INCL */