/* Concatenate two arbitrary file names.

   Copyright (C) 1996-2007, 2009-2016 Free Software Foundation, Inc.

   This program 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.

   This program 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/>.  */

/* Written by Jim Meyering.  */

#include <config.h>

/* Specification.  */
#include "filenamecat.h"

#include <stdlib.h>
#include <string.h>

#include "dirname.h"

#if ! HAVE_MEMPCPY && ! defined mempcpy
# define mempcpy(D, S, N) ((void *) ((char *) memcpy (D, S, N) + (N)))
#endif

/* Return the longest suffix of F that is a relative file name.
   If it has no such suffix, return the empty string.  */

static char const * _GL_ATTRIBUTE_PURE
longest_relative_suffix (char const *f)
{
  for (f += FILE_SYSTEM_PREFIX_LEN (f); ISSLASH (*f); f++)
    continue;
  return f;
}

/* Concatenate two file name components, DIR and ABASE, in
   newly-allocated storage and return the result.
   The resulting file name F is such that the commands "ls F" and "(cd
   DIR; ls BASE)" refer to the same file, where BASE is ABASE with any
   file system prefixes and leading separators removed.
   Arrange for a directory separator if necessary between DIR and BASE
   in the result, removing any redundant separators.
   In any case, if BASE_IN_RESULT is non-NULL, set
   *BASE_IN_RESULT to point to the copy of ABASE in the returned
   concatenation.  However, if ABASE begins with more than one slash,
   set *BASE_IN_RESULT to point to the sole corresponding slash that
   is copied into the result buffer.

   Return NULL if malloc fails.  */

char *
mfile_name_concat (char const *dir, char const *abase, char **base_in_result)
{
  char const *dirbase = last_component (dir);
  size_t dirbaselen = base_len (dirbase);
  size_t dirlen = dirbase - dir + dirbaselen;
  size_t needs_separator = (dirbaselen && ! ISSLASH (dirbase[dirbaselen - 1]));

  char const *base = longest_relative_suffix (abase);
  size_t baselen = strlen (base);

  char *p_concat = malloc (dirlen + needs_separator + baselen + 1);
  char *p;

  if (p_concat == NULL)
    return NULL;

  p = mempcpy (p_concat, dir, dirlen);
  *p = DIRECTORY_SEPARATOR;
  p += needs_separator;

  if (base_in_result)
    *base_in_result = p - IS_ABSOLUTE_FILE_NAME (abase);

  p = mempcpy (p, base, baselen);
  *p = '\0';

  return p_concat;
}