/**
 * slibc — Yet another C library
 * Copyright © 2015  Mattias Andrée (maandree@member.fsf.org)
 * 
 * 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/>.
 */
#include <slib-human.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/stat.h>



/**
 * Parses a human representation of file permissions, and updates to file permissions.
 * 
 * Assuming the current file permissions is `value`, and neither
 * `mode` nor `mask` is `NULL`, the new permissions should be
 * `value & ~*mask | *mode`. The new mode (includes file type) should
 * be `value & ~*mask | *mode & 07777`.
 * 
 * @param   mode  Output parameter for the bits to set, may be `NULL`.
 * @param   mask  Output parameter for the bits to update, may be `NULL`.
 * @param   str   The file permission to parse, must not include file type or be `NULL`.
 * @return        Zero on success, -1 on error.
 * 
 * @throws  EINVAL  If `str` is not parseable.
 */
int machinemode(mode_t* restrict mode, mode_t* restrict mask, const char* restrict str)
{
#define  S_ISUSR  (S_ISUID | S_IXUSR)
#define  S_ISGRP  (S_ISGID | S_IXGRO)
#define  S_ISOTH  (S_ISVTX | S_IXOTH)

#define  TEST_(S, T, V)  (strstarts(str, S) && !(T & (v = V)))
#define  TEST(S, T)      (TEST_(S"+", T, 1) || TEST_(S"-", T, 2) || TEST_(S"=", T, 3))
#define  TESTV(T)        (TEST(#T, T) ? (T = v) : 0)

#define  BITS_(V, T, S)  if (V & bits[i][T])  goto invalid;  else  V |= bits[i][S]
#define  BITS(V)  \
  if      (*str == 'r')  { BITS_(V, 0, 0); }  \
  else if (*str == 'w')  { BITS_(V, 1, 1); }  \
  else if (*str == 'x')  { BITS_(V, 3, 2); }  \
  else if (*str == 's')  { BITS_(V, 3, 3); }  \
  else if (*str == 't')  { BITS_(V, 3, 3); }  \
  else if (*str == 'S')  { BITS_(V, 3, 4); }  \
  else if (*str == 'T')  { BITS_(V, 3, 4); }  \
  else if (*str != '-')  goto invalid
  
  int i, j, n, u = 0, g = 0, o = 0, v;
  char s;
  mode_t or = 0, andn = 0, part;
  mode_t bits[][] = {
    {S_IRUSR, S_IWUSR, S_IXUSR, S_ISUSR, S_ISUID},
    {S_IRGRP, S_IWGRP, S_IXGRP, S_ISGRP, S_ISGID},
    {S_IROTH, S_IWOTH, S_IXOTH, S_ISOTH, S_ISVTX},
  };
  
  switch (*str)
    {
    case '\0':
      goto invalid;
      
    case 'a': case 'u': case 'g': case 'o':
      /* Partial, symbolic. */
      for (; *str; str++)
	{
	  if (TEST("a", u|g|o))  i = 3, u |= v, g |= v, o |= v;
	  else if (TESTV(u))     i = 0;
	  else if (TESTV(g))     i = 1;
	  else if (TESTV(o))     i = 2;
	  else
	    goto invalid;
	  if (n < 3)  n = i + 1;
	  else        n = i, i = 0;
	  s = str[1], str += 2;
	  for (part = 0; *str && (*str != ','); str++)
	    for (j = i; j < n; j++)
	      BITS(part);
	  if (s != '-')  or   |= part;
	  if (s != '=')  andn |= part;
	  else
	    for (j = i; j < n; j++)
	      andn |= bits[i][0] | bits[i][1] | bits[i][3];
	}
      break;
      
    case 'r': case 'w': case 'x': case '-':
    case 's': case 'S': case 't': case 'T':
      /* Exact, symbolic. */
      for (andn = 07777, i = 0; i < 3; i++)
	for (j = 0; j < 3; j++, str++)
	  BITS(or);
      break;
      
    default:
      /* Exact, numeric. */
      for (andn = 07777; (s = *str); str++)
	if (('0' > s) || (s > '7') || (or = (or << 3) | (s & 15), or > 07777))
	  goto invalid;
      break;
    }
  
  if (mode)  *mode = or;
  if (mask)  *mask = andn;
  return 0;
  
 invalid:
  return errno = EINVAL, -1;
}