%{
/*-
 * Written by Pace Willisson (pace@blitz.com)
 * and placed in the public domain.
 *
 * Largely rewritten by J.T. Conklin (jtc@wimsey.com)
 */

#include <sys/types.h>

#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <inttypes.h>
#include <limits.h>
#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <regex.h>
#include <unistd.h>

/*
 * POSIX specifies a specific error code for syntax errors.  We exit
 * with this code for all errors.
 */
#define ERR_EXIT        2

enum valtype {
        integer, numeric_string, string
} ;

struct val {
        enum valtype type;
        union {
                char *s;
                intmax_t i;
        } u;
} ;

char            **av;
int             nonposix;
struct val      *result;

void            assert_to_integer(struct val *);
void            assert_div(intmax_t, intmax_t);
void            assert_minus(intmax_t, intmax_t, intmax_t);
void            assert_plus(intmax_t, intmax_t, intmax_t);
void            assert_times(intmax_t, intmax_t, intmax_t);
int             compare_vals(struct val *, struct val *);
void            free_value(struct val *);
int             is_integer(const char *);
int             is_string(struct val *);
int             is_zero_or_null(struct val *);
struct val      *make_integer(intmax_t);
struct val      *make_str(const char *);
struct val      *op_and(struct val *, struct val *);
struct val      *op_colon(struct val *, struct val *);
struct val      *op_div(struct val *, struct val *);
struct val      *op_eq(struct val *, struct val *);
struct val      *op_ge(struct val *, struct val *);
struct val      *op_gt(struct val *, struct val *);
struct val      *op_le(struct val *, struct val *);
struct val      *op_lt(struct val *, struct val *);
struct val      *op_minus(struct val *, struct val *);
struct val      *op_ne(struct val *, struct val *);
struct val      *op_or(struct val *, struct val *);
struct val      *op_plus(struct val *, struct val *);
struct val      *op_rem(struct val *, struct val *);
struct val      *op_times(struct val *, struct val *);
int             to_integer(struct val *);
void            to_string(struct val *);
int             yyerror(const char *);
int             yylex(void);

%}

%union
{
        struct val *val;
}

%left <val> '|'
%left <val> '&'
%left <val> '=' '>' '<' GE LE NE
%left <val> '+' '-'
%left <val> '*' '/' '%'
%left <val> ':'

%token <val> TOKEN
%type <val> start expr

%%

start: expr { result = $$; }

expr:   TOKEN
        | '(' expr ')' { $$ = $2; }
        | expr '|' expr { $$ = op_or($1, $3); }
        | expr '&' expr { $$ = op_and($1, $3); }
        | expr '=' expr { $$ = op_eq($1, $3); }
        | expr '>' expr { $$ = op_gt($1, $3); }
        | expr '<' expr { $$ = op_lt($1, $3); }
        | expr GE expr  { $$ = op_ge($1, $3); }
        | expr LE expr  { $$ = op_le($1, $3); }
        | expr NE expr  { $$ = op_ne($1, $3); }
        | expr '+' expr { $$ = op_plus($1, $3); }
        | expr '-' expr { $$ = op_minus($1, $3); }
        | expr '*' expr { $$ = op_times($1, $3); }
        | expr '/' expr { $$ = op_div($1, $3); }
        | expr '%' expr { $$ = op_rem($1, $3); }
        | expr ':' expr { $$ = op_colon($1, $3); }
        ;

%%

struct val *
make_integer(intmax_t i)
{
        struct val *vp;

        vp = (struct val *)malloc(sizeof(*vp));
        if (vp == NULL)
                errx(ERR_EXIT, "malloc() failed");

        vp->type = integer;
        vp->u.i  = i;
        return (vp);
}

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

        vp = (struct val *)malloc(sizeof(*vp));
        if (vp == NULL || ((vp->u.s = strdup(s)) == NULL))
                errx(ERR_EXIT, "malloc() failed");

        if (is_integer(s))
                vp->type = numeric_string;
        else
                vp->type = string;

        return (vp);
}

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

int
to_integer(struct val *vp)
{
        intmax_t i;

        /* we can only convert numeric_string to integer, here */
        if (vp->type == numeric_string) {
                errno = 0;
                i  = strtoimax(vp->u.s, (char **)NULL, 10);
                /* just keep as numeric_string, if the conversion fails */
                if (errno != ERANGE) {
                        free(vp->u.s);
                        vp->u.i = i;
                        vp->type = integer;
                }
        }
        return (vp->type == integer);
}

void
assert_to_integer(struct val *vp)
{
        if (vp->type == string)
                errx(ERR_EXIT, "not a decimal number: '%s'", vp->u.s);
        if (!to_integer(vp))
                errx(ERR_EXIT, "operand too large: '%s'", vp->u.s);
}

void
to_string(struct val *vp)
{
        char *tmp;

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

        /*
         * log_10(x) ~= 0.3 * log_2(x).  Rounding up gives the number
         * of digits; add one each for the sign and terminating null
         * character, respectively.
         */
#define NDIGITS(x) (3 * (sizeof(x) * CHAR_BIT) / 10 + 1 + 1 + 1)
        tmp = malloc(NDIGITS(vp->u.i));
        if (tmp == NULL)
                errx(ERR_EXIT, "malloc() failed");

        sprintf(tmp, "%jd", vp->u.i);
        vp->type = string;
        vp->u.s  = tmp;
}

int
is_integer(const char *s)
{
        if (nonposix) {
                if (*s == '\0')
                        return (1);
                while (isspace((unsigned char)*s))
                        s++;
        }
        if (*s == '-' || (nonposix && *s == '+'))
                s++;
        if (*s == '\0')
                return (0);
        while (isdigit((unsigned char)*s))
                s++;
        return (*s == '\0');
}

int
is_string(struct val *vp)
{
        /* only TRUE if this string is not a valid integer */
        return (vp->type == string);
}

int
yylex(void)
{
        char *p;

        if (*av == NULL)
                return (0);

        p = *av++;

        if (strlen(p) == 1) {
                if (strchr("|&=<>+-*/%:()", *p))
                        return (*p);
        } else if (strlen(p) == 2 && p[1] == '=') {
                switch (*p) {
                case '>': return (GE);
                case '<': return (LE);
                case '!': return (NE);
                }
        }

        yylval.val = make_str(p);
        return (TOKEN);
}

int
is_zero_or_null(struct val *vp)
{
        if (vp->type == integer)
                return (vp->u.i == 0);

        return (*vp->u.s == 0 || (to_integer(vp) && vp->u.i == 0));
}

int
main(int argc, char *argv[])
{
        int c;

        setlocale(LC_ALL, "");
        if (getenv("EXPR_COMPAT") != NULL
            || check_utility_compat("expr")) {
                av = argv + 1;
                nonposix = 1;
        } else {
                while ((c = getopt(argc, argv, "e")) != -1) {
                        switch (c) {
                        case 'e':
                                nonposix = 1;
                                break;
                        default:
                                errx(ERR_EXIT,
                                    "usage: expr [-e] expression\n");
                        }
                }
                av = argv + optind;
        }

        yyparse();

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

        return (is_zero_or_null(result));
}

int
yyerror(const char *s __unused)
{
        errx(ERR_EXIT, "syntax error");
}

struct val *
op_or(struct val *a, struct val *b)
{
        if (!is_zero_or_null(a)) {
                free_value(b);
                return (a);
        }
        free_value(a);
        if (!is_zero_or_null(b))
                return (b);
        free_value(b);
        return (make_integer((intmax_t)0));
}

struct val *
op_and(struct val *a, struct val *b)
{
        if (is_zero_or_null(a) || is_zero_or_null(b)) {
                free_value(a);
                free_value(b);
                return (make_integer((intmax_t)0));
        } else {
                free_value(b);
                return (a);
        }
}

int
compare_vals(struct val *a, struct val *b)
{
        int r;

        if (is_string(a) || is_string(b)) {
                to_string(a);
                to_string(b);
                r = strcoll(a->u.s, b->u.s);
        } else {
                assert_to_integer(a);
                assert_to_integer(b);
                if (a->u.i > b->u.i)
                        r = 1;
                else if (a->u.i < b->u.i)
                        r = -1;
                else
                        r = 0;
        }

        free_value(a);
        free_value(b);
        return (r);
}

struct val *
op_eq(struct val *a, struct val *b)
{
        return (make_integer((intmax_t)(compare_vals(a, b) == 0)));
}

struct val *
op_gt(struct val *a, struct val *b)
{
        return (make_integer((intmax_t)(compare_vals(a, b) > 0)));
}

struct val *
op_lt(struct val *a, struct val *b)
{
        return (make_integer((intmax_t)(compare_vals(a, b) < 0)));
}

struct val *
op_ge(struct val *a, struct val *b)
{
        return (make_integer((intmax_t)(compare_vals(a, b) >= 0)));
}

struct val *
op_le(struct val *a, struct val *b)
{
        return (make_integer((intmax_t)(compare_vals(a, b) <= 0)));
}

struct val *
op_ne(struct val *a, struct val *b)
{
        return (make_integer((intmax_t)(compare_vals(a, b) != 0)));
}

void
assert_plus(intmax_t a, intmax_t b, intmax_t r)
{
        /*
         * sum of two positive numbers must be positive,
         * sum of two negative numbers must be negative
         */
        if ((a > 0 && b > 0 && r <= 0) ||
            (a < 0 && b < 0 && r >= 0))
                errx(ERR_EXIT, "overflow");
}

struct val *
op_plus(struct val *a, struct val *b)
{
        struct val *r;

        assert_to_integer(a);
        assert_to_integer(b);
        r = make_integer(a->u.i + b->u.i);
        assert_plus(a->u.i, b->u.i, r->u.i);

        free_value(a);
        free_value(b);
        return (r);
}

void
assert_minus(intmax_t a, intmax_t b, intmax_t r)
{
        if ((a >= 0 && b < 0 && r <= 0) ||
            (a < 0 && b > 0 && r >= 0))
                errx(ERR_EXIT, "overflow");
}

struct val *
op_minus(struct val *a, struct val *b)
{
        struct val *r;

        assert_to_integer(a);
        assert_to_integer(b);
        r = make_integer(a->u.i - b->u.i);
        assert_minus(a->u.i, b->u.i, r->u.i);

        free_value(a);
        free_value(b);
        return (r);
}

/*
 * We depend on undefined behaviour giving a result (in r).
 * To test this result, pass it as volatile.  This prevents
 * optimizing away of the test based on the undefined behaviour.
 */
void
assert_times(intmax_t a, intmax_t b, volatile intmax_t r)
{
        /*
         * If the first operand is 0, no overflow is possible, 
         * else the result of the division test must match the
         * second operand.
         *
         * Be careful to avoid overflow in the overflow test, as
         * in assert_div().  Overflow in division would kill us
         * with a SIGFPE before getting the test wrong.  In old
         * buggy versions, optimization used to give a null test
         * instead of a SIGFPE.
         */
        if ((a == -1 && b == INTMAX_MIN) || (a != 0 && r / a != b))
                errx(ERR_EXIT, "overflow");
}

struct val *
op_times(struct val *a, struct val *b)
{
        struct val *r;

        assert_to_integer(a);
        assert_to_integer(b);
        r = make_integer(a->u.i * b->u.i);
        assert_times(a->u.i, b->u.i, r->u.i);

        free_value(a);
        free_value(b);
        return (r);
}

void
assert_div(intmax_t a, intmax_t b)
{
        if (b == 0)
                errx(ERR_EXIT, "division by zero");
        /* only INTMAX_MIN / -1 causes overflow */
        if (a == INTMAX_MIN && b == -1)
                errx(ERR_EXIT, "overflow");
}

struct val *
op_div(struct val *a, struct val *b)
{
        struct val *r;

        assert_to_integer(a);
        assert_to_integer(b);
        /* assert based on operands only, not on result */
        assert_div(a->u.i, b->u.i);
        r = make_integer(a->u.i / b->u.i);

        free_value(a);
        free_value(b);
        return (r);
}

struct val *
op_rem(struct val *a, struct val *b)
{
        struct val *r;

        assert_to_integer(a);
        assert_to_integer(b);
        /* pass a=1 to only check for div by zero */
        assert_div(1, b->u.i);
        r = make_integer(a->u.i % b->u.i);

        free_value(a);
        free_value(b);
        return (r);
}

struct val *
op_colon(struct val *a, struct val *b)
{
        regex_t rp;
        regmatch_t rm[2];
        char errbuf[256];
        int eval;
        struct val *v;

        /* coerce both arguments to strings */
        to_string(a);
        to_string(b);

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

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

                } else
                        v = make_integer((intmax_t)(rm[0].rm_eo));
        else
                if (rp.re_nsub == 0)
                        v = make_integer((intmax_t)0);
                else
                        v = make_str("");

        /* free arguments and pattern buffer */
        free_value(a);
        free_value(b);
        regfree(&rp);

        return (v);
}