/*
   expr.c - limited shell-like expression parsing functions
   This file is part of the nss-pam-ldapd library.

   Copyright (C) 2009, 2010, 2011 Arthur de Jong

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   This library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
   02110-1301 USA
*/

#include "config.h"

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

#include "expr.h"
#include "compat/attrs.h"

/* the maximum length of a variable name */
#define MAXVARLENGTH 30

static inline int my_isalpha(const char c)
{
  return ((c>='a')&&(c<='z'))||((c>='A')&&(c<='Z'));
}

static inline int my_isalphanum(const char c)
{
  return my_isalpha(c)||((c>='0')&&(c<='9'));
}

/* return the part of the string that is a valid name */
MUST_USE static const char *parse_name(const char *str,int *ptr,char *buffer,size_t buflen)
{
  int i=0;
  /* clear the buffer */
  buffer[i]='\0';
  /* look for an alpha+alphanumeric* string */
  if (!my_isalpha(str[*ptr]))
    return NULL;
  while (my_isalphanum(str[*ptr])||(str[*ptr]==';'))
  {
    if ((size_t)i>=buflen)
      return NULL;
    buffer[i++]=str[(*ptr)++];
  }
  /* NULL-terminate the string */
  if ((size_t)i>=buflen)
    return NULL;
  buffer[i++]='\0';
  return buffer;
}

/* dummy expander function to always return an empty string */
static const char *empty_expander(const char UNUSED(*name),void UNUSED(*expander_arg))
{
  return "";
}

/* definition of the parse functions (they call eachother) */
MUST_USE static const char *parse_dollar_expression(
              const char *str,int *ptr,char *buffer,size_t buflen,
              expr_expander_func expander,void *expander_arg);
MUST_USE static const char *parse_expression(
              const char *str,int *ptr,int endat,char *buffer,size_t buflen,
              expr_expander_func expander,void *expander_arg);

MUST_USE static const char *parse_dollar_expression(
              const char *str,int *ptr,char *buffer,size_t buflen,
              expr_expander_func expander,void *expander_arg)
{
  char varname[MAXVARLENGTH];
  const char *varvalue;
  if ((buflen<=0)||(buffer==NULL)||(str==NULL)||(ptr==NULL))
    return NULL;
  if (str[*ptr]=='{')
  {
    (*ptr)++;
    /* the first part is always a variable name */
    if (parse_name(str,ptr,varname,sizeof(varname))==NULL)
      return NULL;
    varvalue=expander(varname,expander_arg);
    if (varvalue==NULL)
      varvalue="";
    if (str[*ptr]=='}')
    {
      /* simple substitute */
      if (strlen(varvalue)>=buflen)
        return NULL;
      strcpy(buffer,varvalue);
    }
    else if (strncmp(str+*ptr,":-",2)==0)
    {
      /* if variable is not set or empty, substitute remainder */
      (*ptr)+=2;
      if ((varvalue!=NULL)&&(*varvalue!='\0'))
      {
        /* value is set, skip rest of expression and use value */
        if (parse_expression(str,ptr,'}',buffer,buflen,empty_expander,NULL)==NULL)
          return NULL;
        if (strlen(varvalue)>=buflen)
          return NULL;
        strcpy(buffer,varvalue);
      }
      else
      {
        /* value is not set, evaluate rest of expression */
        if (parse_expression(str,ptr,'}',buffer,buflen,expander,expander_arg)==NULL)
          return NULL;
      }
    }
    else if (strncmp(str+*ptr,":+",2)==0)
    {
      /* if variable is set, substitute remainer */
      (*ptr)+=2;
      if ((varvalue!=NULL)&&(*varvalue!='\0'))
      {
        /* value is set, evaluate rest of expression */
        if (parse_expression(str,ptr,'}',buffer,buflen,expander,expander_arg)==NULL)
          return NULL;
      }
      else
      {
        /* value is not set, skip rest of expression and blank */
        if (parse_expression(str,ptr,'}',buffer,buflen,empty_expander,NULL)==NULL)
          return NULL;
        buffer[0]='\0';
      }
    }
    else
      return NULL;
    (*ptr)++; /* skip closing } */
  }
  else
  {
    /* it is a simple reference to a variable, like $uidNumber */
    if (parse_name(str,ptr,varname,sizeof(varname))==NULL)
      return NULL;
    varvalue=expander(varname,expander_arg);
    if (varvalue==NULL)
      varvalue="";
    if (strlen(varvalue)>=buflen)
      return NULL;
    strcpy(buffer,varvalue);
  }
  return buffer;
}

MUST_USE static const char *parse_expression(
              const char *str,int *ptr,int endat,char *buffer,size_t buflen,
              expr_expander_func expander,void *expander_arg)
{
  int j=0;
  /* go over string */
  while ((str[*ptr]!=endat)&&(str[*ptr]!='\0'))
  {
    switch (str[*ptr])
    {
      case '$': /* beginning of an expression */
        (*ptr)++;
        if ((size_t)j>=buflen)
          return NULL;
        if (parse_dollar_expression(str,ptr,buffer+j,buflen-j,expander,expander_arg)==NULL)
          return NULL;
        j=strlen(buffer);
        break;
      case '\\': /* escaped character, unescape */
        (*ptr)++;
      default: /* just copy the text */
        if ((size_t)j>=buflen)
          return NULL;
        buffer[j++]=str[*ptr];
        (*ptr)++;
    }
  }
  /* NULL-terminate buffer */
  if ((size_t)j>=buflen)
    return NULL;
  buffer[j++]='\0';
  return buffer;
}

MUST_USE const char *expr_parse(const char *str,char *buffer,size_t buflen,
                                expr_expander_func expander,void *expander_arg)

{
  int i=0;
  return parse_expression(str,&i,'\0',buffer,buflen,expander,expander_arg);
}

SET *expr_vars(const char *str,SET *set)
{
  char varname[MAXVARLENGTH];
  int i=0;
  /* allocate set if needed */
  if (set==NULL)
    set=set_new();
  if (set==NULL)
    return NULL;
  /* go over string */
  while (str[i]!='\0')
  {
    switch (str[i])
    {
      case '$': /* beginning of a $-expression */
        i++;
        if (str[i]=='{')
          i++;
        /* the rest should start with a variable name */
        if (parse_name(str,&i,varname,sizeof(varname))!=NULL)
          set_add(set,varname);
        break;
      case '\\': /* escaped character, unescape */
        i++;
        /* no break needed here */
      default: /* just skip */
        i++;
    }
  }
  return set;
}