/* vi: set ts=2:
 *
 *	
 *	Eressea PB(E)M host Copyright (C) 1998
 *		Enno Rehling (rehling@usa.net)
 *		Christian Schlittchen (corwin@amber.kn-bremen.de)
 *		Katja Zedel (katze@felidae.kn-bremen.de)
 *		Henning Peters (faroul@beyond.kn-bremen.de)
 *
 *  based on:
 *
 * Atlantis v1.0  13 September 1993 Copyright 1993 by Russell Wallace
 * Atlantis v1.7                    Copyright 1996 by Alex Schröder
 *
 * This program may not be used, modified or distributed. It may not be
 * sold or used commercially without prior written permission from the
 * authors.
 */

#include <platform.h>
#include "rng.h"

#include <assert.h>
#include <stdlib.h>
#include <ctype.h>

/** rolls a number of n-sided dice.
 * Usage: 3d6-3d4+5 = dice(3,6)-dice(3,4)+5 */
int dice(int count, int value)
{
  int d = 0, c;

  if (value <= 0)
    return 0;                   /* (enno) %0 geht nicht. echt wahr. */
  if (count >= 0)
    for (c = count; c > 0; c--)
      d += rng_int() % value + 1;
  else
    for (c = count; c < 0; c++)
      d -= rng_int() % value + 1;

  return d;
}

static int term_eval(const char **sptr)
{
  const char *c = *sptr;
  int m = 0, d = 0, k = 0, term = 1, multi = 1;
  int state = 1;

  for (;;) {
    if (isdigit(*(unsigned char *)c)) {
      k = k * 10 + (*c - '0');
    } else if (*c == '+' || *c == '-' || *c == 0 || *c == '*' || *c == ')'
      || *c == '(') {
      if (state == 1)           /* konstante k addieren */
        m += k * multi;
      else if (state == 2) {    /* dDk */
        int i;
        if (k == 0)
          k = 6;                /* 3d == 3d6 */
        for (i = 0; i != d; ++i)
          m += (1 + rng_int() % k) * multi;
      } else
        assert(!"dice_rand: illegal token");
      if (*c == '*') {
        term *= m;
        m = 0;
      }
      k = d = 0;
      state = 1;
      multi = (*c == '-') ? -1 : 1;

      if (*c == '(') {
        ++c;
        k = term_eval(&c);
      } else if (*c == 0 || *c == ')') {
        break;
      }
    } else if (*c == 'd' || *c == 'D') {
      if (k == 0)
        k = 1;                  /* d9 == 1d9 */
      assert(state == 1 || !"dice_rand: illegal token");
      d = k;
      k = 0;
      state = 2;
    }
    c++;
  }
  *sptr = c;
  return m * term;
}

int dice_rand(const char *s)
{
  return term_eval(&s);
}