/*	$OpenBSD: getusershell.c,v 1.18 2019/12/10 02:35:16 millert Exp $ */
/*
 * Copyright (c) 1985, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <paths.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

/*
 * Local shells should NOT be added here.  They should be added in
 * /etc/shells.
 */

static char *okshells[] = {_PATH_BSHELL, _PATH_CSHELL, _PATH_KSHELL, NULL};
static char **curshell, **shells;
static char **initshells(void);

/*
 * Get a list of shells from _PATH_SHELLS, if it exists.
 */
const char *getusershell(void) {
  char *ret;

  if (curshell == NULL)
    curshell = initshells();
  ret = *curshell;
  if (ret != NULL)
    curshell++;
  return (ret);
}

void endusershell(void) {
  char **s;

  if ((s = shells))
    while (*s)
      free(*s++);
  free(shells);
  shells = NULL;

  curshell = NULL;
}

void setusershell(void) {

  curshell = initshells();
}

static char **initshells(void) {
  size_t nshells, nalloc, linesize;
  char *line;
  FILE *fp;

  free(shells);
  shells = NULL;

  if ((fp = fopen(_PATH_SHELLS, "re")) == NULL)
    return (okshells);

  line = NULL;
  nalloc = 10; // just an initial guess
  nshells = 0;
  shells = reallocarray(NULL, nalloc, sizeof(char *));
  if (shells == NULL)
    goto fail;
  linesize = 0;
  while (getline(&line, &linesize, fp) != -1) {
    if (*line != '/')
      continue;
    line[strcspn(line, "#\n")] = '\0';
    if (!(shells[nshells] = strdup(line)))
      goto fail;

    if (nshells + 1 == nalloc) {
      char **new = reallocarray(shells, nalloc * 2, sizeof(char *));
      if (!new)
        goto fail;
      shells = new;
      nalloc *= 2;
    }
    nshells++;
  }
  free(line);
  shells[nshells] = NULL;
  (void)fclose(fp);
  return (shells);

fail:
  free(line);
  while (nshells)
    free(shells[nshells--]);
  free(shells);
  shells = NULL;
  (void)fclose(fp);
  return (okshells);
}
