/* Written by Jim Meyering.  */

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

#include <stdlib.h>
#include <string.h>
#include "xalloc.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 *
longest_relative_suffix(char const *f) {
    for (f += 0; ((*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 && !((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 = '/';
    p += needs_separator;

    if (base_in_result)
        *base_in_result = p - (abase[0] == '/');

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

    return p_concat;
}

/* Written by Jim Meyering.  */

/* Just like |mfile_name_concat| (|filenamecat-lgpl.c|), except,
   rather than returning |NULL| upon |malloc| failure, here, we report
   the "memory exhausted" condition and exit.  */

char *
file_name_concat(char const *dir, char const *abase, char **base_in_result) {
    char *p = mfile_name_concat(dir, abase, base_in_result);
    if (p == NULL)
        xalloc_die();
    return p;
}