/* expr -- evaluate expressions.
   Copyright (C) 1986, 1991 Free Software Foundation, Inc.

   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 2, 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, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */

/* Author: Mike Parker.

   This program evaluates expressions.  Each token (operator, operand,
   parenthesis) of the expression must be a seperate argument.  The
   parser used is a reasonably general one, though any incarnation of
   it is language-specific.  It is especially nice for expressions.

   No parse tree is needed; a new node is evaluated immediately.
   One function can handle multiple operators all of equal precedence,
   provided they all associate ((x op x) op x).

   Define EVAL_TRACE to print an evaluation trace.  */

#include <stdio.h>
#include <ctype.h>
#include <sys/types.h>
#include <regex.h>
#include "system.h"

#if !__STDC__
#define const
#endif

#define NEW(type) ((type *) xmalloc (sizeof (type)))
#define OLD(x) free ((char *) x)

/* The kinds of value we can have.  */
enum valtype
{
  integer,
  string
};
typedef enum valtype TYPE;

/* A value is.... */
struct valinfo
{
  TYPE type;			/* Which kind. */
  union
  {				/* The value itself. */
    int i;
    char *s;
  } u;
};
typedef struct valinfo VALUE;

/* The arguments given to the program, minus the program name.  */
static char **args;

/* The name this program was run with. */
char *program_name;

void error ();
char *xstrdup ();
char *strstr ();
char *xmalloc ();

static VALUE *docolon ();
static VALUE *eval ();
static VALUE *int_value ();
static VALUE *str_value ();
static int isstring ();
static int nextarg ();
static int nomoreargs ();
static int null ();
static int toarith ();
static void freev ();
static void printv ();
static void tostring ();

#ifdef EVAL_TRACE
static void trace ();
#endif

void
main (argc, argv)
     int argc;
     char **argv;
{
  VALUE *v;

  program_name = argv[0];

  if (argc == 1)
    {
      fprintf (stderr, "Usage: %s expression...\n", argv[0]);
      exit (1);
    }
  args = argv + 1;

  v = eval ();
  if (!nomoreargs ())
    error (2, 0, "syntax error");
  printv (v);

  exit (null (v));
}

/* Return a VALUE for I.  */

static VALUE *
int_value (i)
     int i;
{
  VALUE *v;

  v = NEW (VALUE);
  v->type = integer;
  v->u.i = i;
  return v;
}

/* Return a VALUE for S.  */

static VALUE *
str_value (s)
     char *s;
{
  VALUE *v;

  v = NEW (VALUE);
  v->type = string;
  v->u.s = xstrdup (s);
  return v;
}

/* Free VALUE V, including structure components.  */

static void
freev (v)
     VALUE *v;
{
  if (v->type == string)
    free (v->u.s);
  OLD (v);
}

/* Print VALUE V.  */

static void
printv (v)
     VALUE *v;
{
  switch (v->type)
    {
    case integer:
      printf ("%d\n", v->u.i);
      break;
    case string:
      printf ("%s\n", v->u.s);
      break;
    }
}

/* Return nonzero if V is a null-string or zero-number.  */

static int
null (v)
     VALUE *v;
{
  switch (v->type)
    {
    case integer:
      return v->u.i == 0;
    case string:
      return v->u.s[0] == '\0';
    }
}

/* Return nonzero if V is a string value.  */

static int
isstring (v)
     VALUE *v;
{
  return v->type == string;
}

/* Coerce V to a string value (can't fail).  */

static void
tostring (v)
     VALUE *v;
{
  char *temp;

  switch (v->type)
    {
    case integer:
      temp = xmalloc (4 * (sizeof (int) / sizeof (char)));
      sprintf (temp, "%d", v->u.i);
      v->u.s = temp;
      v->type = string;
      break;
    case string:
      break;
    }
}

/* Coerce V to an integer value.  Return 1 on success, 0 on failure.  */

static int
toarith (v)
     VALUE *v;
{
  int i;
  int neg;
  char *cp;

  switch (v->type)
    {
    case integer:
      return 1;
    case string:
      i = 0;
      cp = v->u.s;
      neg = (*cp == '-');
      if (neg)
	cp++;
      for (; *cp; cp++)
	{
	  if (isdigit (*cp))
	    i = i * 10 + *cp - '0';
	  else
	    return 0;
	}
      free (v->u.s);
      v->u.i = i * (neg ? -1 : 1);
      v->type = integer;
      return 1;
    }
}

/* Return nonzero if the next token matches STR exactly.
   STR must not be NULL.  */

static int
nextarg (str)
     char *str;
{
  if (*args == NULL)
    return 0;
  return strcmp (*args, str) == 0;
}

/* Return nonzero if there no more tokens.  */

static int
nomoreargs ()
{
  return *args == 0;
}

/* The comparison operator handling functions.  */

#define cmpf(name, rel)				\
static						\
int name (l, r) VALUE *l; VALUE *r;		\
{						\
  if (isstring (l) || isstring (r))		\
    {						\
       tostring (l);				\
       tostring (r);				\
       return strcmp (l->u.s, r->u.s) rel 0;	\
    }						\
 else						\
   return l->u.i rel r->u.i;			\
}
cmpf (less_than, <)
cmpf (less_equal, <=)
cmpf (equal, ==)
cmpf (not_equal, !=)
cmpf (greater_equal, >=)
cmpf (greater_than, >)

#undef cmpf

/* The arithmetic operator handling functions.  */

#define arithf(name, op)			\
static						\
int name (l, r) VALUE *l; VALUE *r;		\
{						\
  if (!toarith (l) || !toarith (r))		\
    error (2, 0, "non-numeric argument");	\
  return l->u.i op r->u.i;			\
}

arithf (plus, +)
arithf (minus, -)
arithf (multiply, *)
arithf (divide, /)
arithf (mod, %)

#undef arithf

#ifdef EVAL_TRACE
/* Print evaluation trace and args remaining.  */

static void
trace (fxn)
     char *fxn;
{
  char **a;

  printf ("%s:", fxn);
  for (a = args; *a; a++)
    printf (" %s", *a);
  putchar ('\n');
}
#endif

/* Do the : operator.
   SV is the VALUE for the lhs (the string),
   PV is the VALUE for the rhs (the pattern).  */

static VALUE *
docolon (sv, pv)
     VALUE *sv;
     VALUE *pv;
{
  VALUE *v;
  const char *errmsg;
  struct re_pattern_buffer re_buffer;
  struct re_registers re_regs;
  int len;

  tostring (sv);
  tostring (pv);

  len = strlen (pv->u.s);
  re_buffer.allocated = 2 * len;
  re_buffer.buffer = (unsigned char *) xmalloc (re_buffer.allocated);
  re_buffer.translate = 0;
  errmsg = re_compile_pattern (pv->u.s, len, &re_buffer);
  if (errmsg)
    error (2, 0, "%s", errmsg);

  len = re_match (&re_buffer, sv->u.s, strlen (sv->u.s), 0, &re_regs);
  if (len >= 0)
    {
      /* Were \(...\) used? */
      if (re_buffer.re_nsub > 0)/* was (re_regs.start[1] >= 0) */
	{
	  sv->u.s[re_regs.end[1]] = '\0';
	  v = str_value (sv->u.s + re_regs.start[1]);
	}
      else
	v = int_value (len);
    }
  else
    {
      /* Match failed -- return the right kind of null.  */
      if (strstr (pv->u.s, "\\("))
	v = str_value ("");
      else
	v = int_value (0);
    }
  free (re_buffer.buffer);
  return v;
}

/* Handle bare operands and ( expr ) syntax.  */

static VALUE *
eval7 ()
{
  VALUE *v;

#ifdef EVAL_TRACE
  trace ("eval7");
#endif
  if (nomoreargs ())
    error (2, 0, "syntax error");
  else if (nextarg ("("))
    {
      args++;
      v = eval ();
      if (!nextarg (")"))
	error (2, 0, "syntax error");
      args++;
      return v;
    }
  else if (nextarg (")"))
    error (2, 0, "syntax error");
  else
    return str_value (*args++);
}

/* Handle match, substr, index, and length keywords.  */

static VALUE *
eval6 ()
{
  VALUE *l;
  VALUE *r;
  VALUE *v;
  VALUE *i1;
  VALUE *i2;

#ifdef EVAL_TRACE
  trace ("eval6");
#endif
  if (nextarg ("length"))
    {
      args++;
      r = eval6 ();
      tostring (r);
      v = int_value (strlen (r->u.s));
      freev (r);
      return v;
    }
  else if (nextarg ("match"))
    {
      args++;
      l = eval6 ();
      r = eval6 ();
      v = docolon (l, r);
      freev (l);
      freev (r);
      return v;
    }
  else if (nextarg ("index"))
    {
      args++;
      l = eval6 ();
      r = eval6 ();
      tostring (l);
      tostring (r);
      v = int_value (strcspn (l->u.s, r->u.s) + 1);
      if (v->u.i == strlen (l->u.s) + 1)
	v->u.i = 0;
      freev (l);
      freev (r);
      return v;
    }
  else if (nextarg ("substr"))
    {
      args++;
      l = eval6 ();
      i1 = eval6 ();
      i2 = eval6 ();
      tostring (l);
      if (!toarith (i1) || !toarith (i2)
	  || i1->u.i > strlen (l->u.s)
	  || i1->u.i <= 0 || i2->u.i <= 0)
	v = str_value ("");
      else
	{
	  v = NEW (VALUE);
	  v->type = string;
	  v->u.s = strncpy ((char *) xmalloc (i2->u.i + 1),
			    l->u.s + i1->u.i - 1, i2->u.i);
	}
      freev (l);
      freev (i1);
      freev (i2);
      return v;
    }
  else
    return eval7 ();
}

/* Handle : operator (pattern matching).
   Calls docolon to do the real work.  */

static VALUE *
eval5 ()
{
  VALUE *l;
  VALUE *r;
  VALUE *v;

#ifdef EVAL_TRACE
  trace ("eval5");
#endif
  l = eval6 ();
  while (1)
    {
      if (nextarg (":"))
	{
	  args++;
	  r = eval6 ();
	  v = docolon (l, r);
	  freev (l);
	  freev (r);
	  l = v;
	}
      else
	return l;
    }
}

/* Handle *, /, % operators.  */

static VALUE *
eval4 ()
{
  VALUE *l;
  VALUE *r;
  int (*fxn) ();
  int val;

#ifdef EVAL_TRACE
  trace ("eval4");
#endif
  l = eval5 ();
  while (1)
    {
      if (nextarg ("*"))
	fxn = multiply;
      else if (nextarg ("/"))
	fxn = divide;
      else if (nextarg ("%"))
	fxn = mod;
      else
	return l;
      args++;
      r = eval5 ();
      val = (*fxn) (l, r);
      freev (l);
      freev (r);
      l = int_value (val);
    }
}

/* Handle +, - operators.  */

static VALUE *
eval3 ()
{
  VALUE *l;
  VALUE *r;
  int (*fxn) ();
  int val;

#ifdef EVAL_TRACE
  trace ("eval3");
#endif
  l = eval4 ();
  while (1)
    {
      if (nextarg ("+"))
	fxn = plus;
      else if (nextarg ("-"))
	fxn = minus;
      else
	return l;
      args++;
      r = eval4 ();
      val = (*fxn) (l, r);
      freev (l);
      freev (r);
      l = int_value (val);
    }
}

/* Handle comparisons.  */

static VALUE *
eval2 ()
{
  VALUE *l;
  VALUE *r;
  int (*fxn) ();
  int val;

#ifdef EVAL_TRACE
  trace ("eval2");
#endif
  l = eval3 ();
  while (1)
    {
      if (nextarg ("<"))
	fxn = less_than;
      else if (nextarg ("<="))
	fxn = less_equal;
      else if (nextarg ("=") || nextarg ("=="))
	fxn = equal;
      else if (nextarg ("!="))
	fxn = not_equal;
      else if (nextarg (">="))
	fxn = greater_equal;
      else if (nextarg (">"))
	fxn = greater_than;
      else
	return l;
      args++;
      r = eval3 ();
      toarith (l);
      toarith (r);
      val = (*fxn) (l, r);
      freev (l);
      freev (r);
      l = int_value (val);
    }
}

/* Handle &.  */

static VALUE *
eval1 ()
{
  VALUE *l;
  VALUE *r;

#ifdef EVAL_TRACE
  trace ("eval1");
#endif
  l = eval2 ();
  while (1)
    {
      if (nextarg ("&"))
	{
	  args++;
	  r = eval2 ();
	  if (null (l) || null (r))
	    {
	      freev (l);
	      freev (r);
	      l = int_value (0);
	    }
	  else
	    freev (r);
	}
      else
	return l;
    }
}

/* Handle |.  */

static VALUE *
eval ()
{
  VALUE *l;
  VALUE *r;

#ifdef EVAL_TRACE
  trace ("eval");
#endif
  l = eval1 ();
  while (1)
    {
      if (nextarg ("|"))
	{
	  args++;
	  r = eval1 ();
	  if (null (l))
	    {
	      freev (l);
	      l = r;
	    }
	  else
	    freev (r);
	}
      else
	return l;
    }
}