/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-â
âvi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :viâ
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â Copyright 2022 Justine Alexandra Roberts Tunney                              â
â                                                                              â
â Permission to use, copy, modify, and/or distribute this software for         â
â any purpose with or without fee is hereby granted, provided that the         â
â above copyright notice and this permission notice appear in all copies.      â
â                                                                              â
â THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                â
â WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                â
â WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             â
â AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         â
â DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        â
â PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               â
â TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             â
â PERFORMANCE OF THIS SOFTWARE.                                                â
ââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââ*/
#include "libc/intrin/bits.h"
#include "libc/str/path.h"
#include "libc/str/str.h"
#include "libc/sysv/errfuns.h"

/**
 * Joins paths, e.g.
 *
 *     0    + 0    â 0
 *     ""   + ""   â ""
 *     "a"  + 0    â "a"
 *     "a"  + ""   â "a/"
 *     0    + "b"  â "b"
 *     ""   + "b"  â "b"
 *     "."  + "b"  â "./b"
 *     "b"  + "."  â "b/."
 *     "a"  + "b"  â "a/b"
 *     "a/" + "b"  â "a/b"
 *     "a"  + "b/" â "a/b/"
 *     "a"  + "/b" â "/b"
 *
 * @return joined path, which may be `buf`, `path`, or `other`, or null
 *     if (1) `buf` didn't have enough space, or (2) both `path` and
 *     `other` were null
 */
char *_joinpaths(char *buf, size_t size, const char *path, const char *other) {
  size_t pathlen, otherlen;
  if (!other) return path;
  if (!path) return other;
  pathlen = strlen(path);
  if (!pathlen || *other == '/') {
    return (/*unconst*/ char *)other;
  }
  otherlen = strlen(other);
  if (path[pathlen - 1] == '/') {
    if (pathlen + otherlen + 1 <= size) {
      memmove(buf, path, pathlen);
      memmove(buf + pathlen, other, otherlen + 1);
      return buf;
    } else {
      return 0;
    }
  } else {
    if (pathlen + 1 + otherlen + 1 <= size) {
      memmove(buf, path, pathlen);
      buf[pathlen] = '/';
      memmove(buf + pathlen + 1, other, otherlen + 1);
      return buf;
    } else {
      return 0;
    }
  }
}
