/*	$OpenBSD: expr.c,v 1.26 2016/10/19 18:20:25 schwarze Exp $	*/
/*	$NetBSD: expr.c,v 1.3.6.1 1996/06/04 20:41:47 cgd Exp $	*/

/*
 * Written by J.T. Conklin <jtc@netbsd.org>.
 * Public domain.
 */

#define _GNU_SOURCE

#include <ctype.h>
#include <err.h>
#include <limits.h>
#include <regex.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

struct val *make_int(int64_t);
struct val *make_str(char *);
void free_value(struct val *);
int is_integer(struct val *, int64_t *);
int to_integer(struct val *);
void to_string(struct val *);
int is_zero_or_null(struct val *);
void nexttoken(int);
void error(void);
struct val *eval6(void);
struct val *eval5(void);
struct val *eval4(void);
struct val *eval3(void);
struct val *eval2(void);
struct val *eval1(void);
struct val *eval0(void);

enum token {
  OR,
  AND,
  EQ,
  LT,
  GT,
  ADD,
  SUB,
  MUL,
  DIV,
  MOD,
  MATCH,
  RP,
  LP,
  NE,
  LE,
  GE,
  OPERAND,
  EOI
};

struct val {
  enum { integer, string } type;

  union {
    char *s;
    int64_t i;
  } u;
};

enum token token;
struct val *tokval;
char **av;

struct val *make_int(int64_t i) {
  struct val *vp;

  vp = malloc(sizeof(*vp));
  if (vp == NULL) {
    err(3, NULL);
  }
  vp->type = integer;
  vp->u.i = i;
  return vp;
}

struct val *make_str(char *s) {
  struct val *vp;

  vp = malloc(sizeof(*vp));
  if (vp == NULL || ((vp->u.s = strdup(s)) == NULL)) {
    err(3, NULL);
  }
  vp->type = string;
  return vp;
}

void free_value(struct val *vp) {
  if (vp->type == string)
    free(vp->u.s);
  free(vp);
}

/* determine if vp is an integer; if so, return it's value in *r */
int is_integer(struct val *vp, int64_t *r) {
  char *s;
  int neg;
  int64_t i;

  if (vp->type == integer) {
    *r = vp->u.i;
    return 1;
  }

  /*
   * POSIX.2 defines an "integer" as an optional unary minus
   * followed by digits.
   */
  s = vp->u.s;
  i = 0;

  neg = (*s == '-');
  if (neg)
    s++;

  while (*s) {
    if (!isdigit((unsigned char)*s))
      return 0;

    i *= 10;
    i += *s - '0';

    s++;
  }

  if (neg)
    i *= -1;

  *r = i;
  return 1;
}

/* coerce to vp to an integer */
int to_integer(struct val *vp) {
  int64_t r;

  if (vp->type == integer)
    return 1;

  if (is_integer(vp, &r)) {
    free(vp->u.s);
    vp->u.i = r;
    vp->type = integer;
    return 1;
  }

  return 0;
}

/* coerce to vp to an string */
void to_string(struct val *vp) {
  char *tmp;

  if (vp->type == string)
    return;

  if (asprintf(&tmp, "%lld", (long long)vp->u.i) == -1)
    err(3, NULL);

  vp->type = string;
  vp->u.s = tmp;
}

int is_zero_or_null(struct val *vp) {
  if (vp->type == integer)
    return vp->u.i == 0;
  else
    return *vp->u.s == 0 || (to_integer(vp) && vp->u.i == 0);
}

void nexttoken(int pat) {
  char *p;

  if ((p = *av) == NULL) {
    token = EOI;
    return;
  }
  av++;

  if (pat == 0 && p[0] != '\0') {
    if (p[1] == '\0') {
      const char *x = "|&=<>+-*/%:()";
      char *i; /* index */

      if ((i = strchr(x, *p)) != NULL) {
        token = i - x;
        return;
      }
    } else if (p[1] == '=' && p[2] == '\0') {
      switch (*p) {
      case '<':
        token = LE;
        return;
      case '>':
        token = GE;
        return;
      case '!':
        token = NE;
        return;
      }
    }
  }
  tokval = make_str(p);
  token = OPERAND;
  return;
}

void error(void) { errx(2, "syntax error"); }

struct val *eval6(void) {
  struct val *v;

  if (token == OPERAND) {
    nexttoken(0);
    return tokval;
  } else if (token == RP) {
    nexttoken(0);
    v = eval0();
    if (token != LP)
      error();
    nexttoken(0);
    return v;
  } else
    error();
  exit(EXIT_FAILURE);
}

/* Parse and evaluate match (regex) expressions */
struct val *eval5(void) {
  regex_t rp;
  regmatch_t rm[2];
  char errbuf[256];
  int eval;
  struct val *l, *r;
  struct val *v;

  l = eval6();
  while (token == MATCH) {
    nexttoken(1);
    r = eval6();

    /* coerce to both arguments to strings */
    to_string(l);
    to_string(r);

    /* compile regular expression */
    if ((eval = regcomp(&rp, r->u.s, 0)) != 0) {
      regerror(eval, &rp, errbuf, sizeof(errbuf));
      errx(2, "%s", errbuf);
    }

    /* compare string against pattern --  remember that patterns
       are anchored to the beginning of the line */
    if (regexec(&rp, l->u.s, 2, rm, 0) == 0 && rm[0].rm_so == 0) {
      if (rm[1].rm_so >= 0) {
        *(l->u.s + rm[1].rm_eo) = '\0';
        v = make_str(l->u.s + rm[1].rm_so);

      } else {
        v = make_int(rm[0].rm_eo - rm[0].rm_so);
      }
    } else {
      if (rp.re_nsub == 0) {
        v = make_int(0);
      } else {
        v = make_str("");
      }
    }

    /* free arguments and pattern buffer */
    free_value(l);
    free_value(r);
    regfree(&rp);

    l = v;
  }

  return l;
}

/* Parse and evaluate multiplication and division expressions */
struct val *eval4(void) {
  struct val *l, *r;
  enum token op;

  l = eval5();
  while ((op = token) == MUL || op == DIV || op == MOD) {
    nexttoken(0);
    r = eval5();

    if (!to_integer(l) || !to_integer(r)) {
      errx(2, "non-numeric argument");
    }

    if (op == MUL) {
      l->u.i *= r->u.i;
    } else {
      if (r->u.i == 0) {
        errx(2, "division by zero");
      }
      if (op == DIV) {
        if (l->u.i != INT64_MIN || r->u.i != -1)
          l->u.i /= r->u.i;
      } else {
        if (l->u.i != INT64_MIN || r->u.i != -1)
          l->u.i %= r->u.i;
        else
          l->u.i = 0;
      }
    }

    free_value(r);
  }

  return l;
}

/* Parse and evaluate addition and subtraction expressions */
struct val *eval3(void) {
  struct val *l, *r;
  enum token op;

  l = eval4();
  while ((op = token) == ADD || op == SUB) {
    nexttoken(0);
    r = eval4();

    if (!to_integer(l) || !to_integer(r)) {
      errx(2, "non-numeric argument");
    }

    if (op == ADD) {
      l->u.i += r->u.i;
    } else {
      l->u.i -= r->u.i;
    }

    free_value(r);
  }

  return l;
}

/* Parse and evaluate comparison expressions */
struct val *eval2(void) {
  struct val *l, *r;
  enum token op;
  int64_t v = 0, li, ri;

  l = eval3();
  while ((op = token) == EQ || op == NE || op == LT || op == GT || op == LE ||
         op == GE) {
    nexttoken(0);
    r = eval3();

    if (is_integer(l, &li) && is_integer(r, &ri)) {
      switch (op) {
      case GT:
        v = (li > ri);
        break;
      case GE:
        v = (li >= ri);
        break;
      case LT:
        v = (li < ri);
        break;
      case LE:
        v = (li <= ri);
        break;
      case EQ:
        v = (li == ri);
        break;
      case NE:
        v = (li != ri);
        break;
      default:
        break;
      }
    } else {
      to_string(l);
      to_string(r);

      switch (op) {
      case GT:
        v = (strcoll(l->u.s, r->u.s) > 0);
        break;
      case GE:
        v = (strcoll(l->u.s, r->u.s) >= 0);
        break;
      case LT:
        v = (strcoll(l->u.s, r->u.s) < 0);
        break;
      case LE:
        v = (strcoll(l->u.s, r->u.s) <= 0);
        break;
      case EQ:
        v = (strcoll(l->u.s, r->u.s) == 0);
        break;
      case NE:
        v = (strcoll(l->u.s, r->u.s) != 0);
        break;
      default:
        break;
      }
    }

    free_value(l);
    free_value(r);
    l = make_int(v);
  }

  return l;
}

/* Parse and evaluate & expressions */
struct val *eval1(void) {
  struct val *l, *r;

  l = eval2();
  while (token == AND) {
    nexttoken(0);
    r = eval2();

    if (is_zero_or_null(l) || is_zero_or_null(r)) {
      free_value(l);
      free_value(r);
      l = make_int(0);
    } else {
      free_value(r);
    }
  }

  return l;
}

/* Parse and evaluate | expressions */
struct val *eval0(void) {
  struct val *l, *r;

  l = eval1();
  while (token == OR) {
    nexttoken(0);
    r = eval1();

    if (is_zero_or_null(l)) {
      free_value(l);
      l = r;
    } else {
      free_value(r);
    }
  }

  return l;
}

int main(int argc, char *argv[]) {
  struct val *vp;

  if (argc > 1 && !strcmp(argv[1], "--"))
    argv++;

  av = argv + 1;

  nexttoken(0);
  vp = eval0();

  if (token != EOI)
    error();

  if (vp->type == integer)
    printf("%lld\n", (long long)vp->u.i);
  else
    printf("%s\n", vp->u.s);

  return is_zero_or_null(vp);
}
