/* vi: set sw=4 ts=4: */
/*
 * Mini expr implementation for busybox
 *
 * based on GNU expr Mike Parker.
 * Copyright (C) 86, 1991-1997, 1999 Free Software Foundation, Inc.
 *
 * Busybox modifications
 * Copyright (c) 2000  Edward Betts <edward@debian.org>.
 * Copyright (C) 2003-2005  Vladimir Oleynik <dzo@simtreas.ru>
 *  - reduced 464 bytes.
 *  - 64 math support
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

/* This program evaluates expressions.  Each token (operator, operand,
 * parenthesis) of the expression must be a separate 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). */

/* no getopt needed */

//usage:#define expr_trivial_usage
//usage:       "EXPRESSION"
//usage:#define expr_full_usage "\n\n"
//usage:       "Print the value of EXPRESSION to stdout\n"
//usage:    "\n"
//usage:       "EXPRESSION may be:\n"
//usage:       "        ARG1 | ARG2     ARG1 if it is neither null nor 0, otherwise ARG2\n"
//usage:       "        ARG1 & ARG2     ARG1 if neither argument is null or 0, otherwise 0\n"
//usage:       "        ARG1 < ARG2     1 if ARG1 is less than ARG2, else 0. Similarly:\n"
//usage:       "        ARG1 <= ARG2\n"
//usage:       "        ARG1 = ARG2\n"
//usage:       "        ARG1 != ARG2\n"
//usage:       "        ARG1 >= ARG2\n"
//usage:       "        ARG1 > ARG2\n"
//usage:       "        ARG1 + ARG2     Sum of ARG1 and ARG2. Similarly:\n"
//usage:       "        ARG1 - ARG2\n"
//usage:       "        ARG1 * ARG2\n"
//usage:       "        ARG1 / ARG2\n"
//usage:       "        ARG1 % ARG2\n"
//usage:       "        STRING : REGEXP         Anchored pattern match of REGEXP in STRING\n"
//usage:       "        match STRING REGEXP     Same as STRING : REGEXP\n"
//usage:       "        substr STRING POS LENGTH Substring of STRING, POS counted from 1\n"
//usage:       "        index STRING CHARS      Index in STRING where any CHARS is found, or 0\n"
//usage:       "        length STRING           Length of STRING\n"
//usage:       "        quote TOKEN             Interpret TOKEN as a string, even if\n"
//usage:       "                                it is a keyword like 'match' or an\n"
//usage:       "                                operator like '/'\n"
//usage:       "        (EXPRESSION)            Value of EXPRESSION\n"
//usage:       "\n"
//usage:       "Beware that many operators need to be escaped or quoted for shells.\n"
//usage:       "Comparisons are arithmetic if both ARGs are numbers, else\n"
//usage:       "lexicographical. Pattern matches return the string matched between\n"
//usage:       "\\( and \\) or null; if \\( and \\) are not used, they return the number\n"
//usage:       "of characters matched or 0."

#include "libbb.h"
#include "xregex.h"

#if ENABLE_EXPR_MATH_SUPPORT_64
typedef int64_t arith_t;

#define PF_REZ      "ll"
#define PF_REZ_TYPE (long long)
#define STRTOL(s, e, b) strtoll(s, e, b)
#else
typedef long arith_t;

#define PF_REZ      "l"
#define PF_REZ_TYPE (long)
#define STRTOL(s, e, b) strtol(s, e, b)
#endif

/* TODO: use bb_strtol[l]? It's easier to check for errors... */

/* The kinds of value we can have.  */
enum {
        INTEGER,
        STRING
};

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

/* The arguments given to the program, minus the program name.  */
struct globals {
        char **args;
} FIX_ALIASING;
#define G (*(struct globals*)&bb_common_bufsiz1)
#define INIT_G() do { } while (0)

/* forward declarations */
static VALUE *eval(void);


/* Return a VALUE for I.  */

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

        v = xzalloc(sizeof(VALUE));
        if (INTEGER) /* otherwise xzaaloc did it already */
                v->type = INTEGER;
        v->u.i = i;
        return v;
}

/* Return a VALUE for S.  */

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

        v = xzalloc(sizeof(VALUE));
        if (STRING) /* otherwise xzaaloc did it already */
                v->type = STRING;
        v->u.s = xstrdup(s);
        return v;
}

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

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

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

static int null(VALUE *v)
{
        if (v->type == INTEGER)
                return v->u.i == 0;
        /* STRING: */
        return v->u.s[0] == '\0' || LONE_CHAR(v->u.s, '0');
}

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

static void tostring(VALUE *v)
{
        if (v->type == INTEGER) {
                v->u.s = xasprintf("%" PF_REZ "d", PF_REZ_TYPE v->u.i);
                v->type = STRING;
        }
}

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

static bool toarith(VALUE *v)
{
        if (v->type == STRING) {
                arith_t i;
                char *e;

                /* Don't interpret the empty string as an integer.  */
                /* Currently does not worry about overflow or int/long differences. */
                i = STRTOL(v->u.s, &e, 10);
                if ((v->u.s == e) || *e)
                        return 0;
                free(v->u.s);
                v->u.i = i;
                v->type = INTEGER;
        }
        return 1;
}

/* Return str[0]+str[1] if the next token matches STR exactly.
   STR must not be NULL.  */

static int nextarg(const char *str)
{
        if (*G.args == NULL || strcmp(*G.args, str) != 0)
                return 0;
        return (unsigned char)str[0] + (unsigned char)str[1];
}

/* The comparison operator handling functions.  */

static int cmp_common(VALUE *l, VALUE *r, int op)
{
        arith_t ll, rr;

        ll = l->u.i;
        rr = r->u.i;
        if (l->type == STRING || r->type == STRING) {
                tostring(l);
                tostring(r);
                ll = strcmp(l->u.s, r->u.s);
                rr = 0;
        }
        /* calculating ll - rr and checking the result is prone to overflows.
         * We'll do it differently: */
        if (op == '<')
                return ll < rr;
        if (op == ('<' + '='))
                return ll <= rr;
        if (op == '=' || (op == '=' + '='))
                return ll == rr;
        if (op == '!' + '=')
                return ll != rr;
        if (op == '>')
                return ll > rr;
        /* >= */
        return ll >= rr;
}

/* The arithmetic operator handling functions.  */

static arith_t arithmetic_common(VALUE *l, VALUE *r, int op)
{
        arith_t li, ri;

        if (!toarith(l) || !toarith(r))
                bb_error_msg_and_die("non-numeric argument");
        li = l->u.i;
        ri = r->u.i;
        if (op == '+')
                return li + ri;
        if (op == '-')
                return li - ri;
        if (op == '*')
                return li * ri;
        if (ri == 0)
                bb_error_msg_and_die("division by zero");
        if (op == '/')
                return li / ri;
        return li % ri;
}

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

static VALUE *docolon(VALUE *sv, VALUE *pv)
{
        enum { NMATCH = 2 };
        VALUE *v;
        regex_t re_buffer;
        regmatch_t re_regs[NMATCH];

        tostring(sv);
        tostring(pv);

        if (pv->u.s[0] == '^') {
                bb_error_msg(
"warning: '%s': using '^' as the first character\n"
"of a basic regular expression is not portable; it is ignored", pv->u.s);
        }

        memset(&re_buffer, 0, sizeof(re_buffer));
        memset(re_regs, 0, sizeof(re_regs));
        xregcomp(&re_buffer, pv->u.s, 0);

        /* expr uses an anchored pattern match, so check that there was a
         * match and that the match starts at offset 0. */
        if (regexec(&re_buffer, sv->u.s, NMATCH, re_regs, 0) != REG_NOMATCH
         && re_regs[0].rm_so == 0
        ) {
                /* Were \(...\) used? */
                if (re_buffer.re_nsub > 0 && re_regs[1].rm_so >= 0) {
                        sv->u.s[re_regs[1].rm_eo] = '\0';
                        v = str_value(sv->u.s + re_regs[1].rm_so);
                } else {
                        v = int_value(re_regs[0].rm_eo);
                }
        } else {
                /* Match failed -- return the right kind of null.  */
                if (re_buffer.re_nsub > 0)
                        v = str_value("");
                else
                        v = int_value(0);
        }
        regfree(&re_buffer);
        return v;
}

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

static VALUE *eval7(void)
{
        VALUE *v;

        if (!*G.args)
                bb_error_msg_and_die("syntax error");

        if (nextarg("(")) {
                G.args++;
                v = eval();
                if (!nextarg(")"))
                        bb_error_msg_and_die("syntax error");
                G.args++;
                return v;
        }

        if (nextarg(")"))
                bb_error_msg_and_die("syntax error");

        return str_value(*G.args++);
}

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

static VALUE *eval6(void)
{
        static const char keywords[] ALIGN1 =
                "quote\0""length\0""match\0""index\0""substr\0";

        VALUE *r, *i1, *i2;
        VALUE *l = l; /* silence gcc */
        VALUE *v = v; /* silence gcc */
        int key = *G.args ? index_in_strings(keywords, *G.args) + 1 : 0;

        if (key == 0) /* not a keyword */
                return eval7();
        G.args++; /* We have a valid token, so get the next argument.  */
        if (key == 1) { /* quote */
                if (!*G.args)
                        bb_error_msg_and_die("syntax error");
                return str_value(*G.args++);
        }
        if (key == 2) { /* length */
                r = eval6();
                tostring(r);
                v = int_value(strlen(r->u.s));
                freev(r);
        } else
                l = eval6();

        if (key == 3) { /* match */
                r = eval6();
                v = docolon(l, r);
                freev(l);
                freev(r);
        }
        if (key == 4) { /* index */
                r = eval6();
                tostring(l);
                tostring(r);
                v = int_value(strcspn(l->u.s, r->u.s) + 1);
                if (v->u.i == (arith_t) strlen(l->u.s) + 1)
                        v->u.i = 0;
                freev(l);
                freev(r);
        }
        if (key == 5) { /* substr */
                i1 = eval6();
                i2 = eval6();
                tostring(l);
                if (!toarith(i1) || !toarith(i2)
                 || i1->u.i > (arith_t) strlen(l->u.s)
                 || i1->u.i <= 0 || i2->u.i <= 0)
                        v = str_value("");
                else {
                        v = xmalloc(sizeof(VALUE));
                        v->type = STRING;
                        v->u.s = xstrndup(l->u.s + i1->u.i - 1, i2->u.i);
                }
                freev(l);
                freev(i1);
                freev(i2);
        }
        return v;
}

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

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

        l = eval6();
        while (nextarg(":")) {
                G.args++;
                r = eval6();
                v = docolon(l, r);
                freev(l);
                freev(r);
                l = v;
        }
        return l;
}

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

static VALUE *eval4(void)
{
        VALUE *l, *r;
        int op;
        arith_t val;

        l = eval5();
        while (1) {
                op = nextarg("*");
                if (!op) { op = nextarg("/");
                 if (!op) { op = nextarg("%");
                  if (!op) return l;
                }}
                G.args++;
                r = eval5();
                val = arithmetic_common(l, r, op);
                freev(l);
                freev(r);
                l = int_value(val);
        }
}

/* Handle +, - operators.  */

static VALUE *eval3(void)
{
        VALUE *l, *r;
        int op;
        arith_t val;

        l = eval4();
        while (1) {
                op = nextarg("+");
                if (!op) {
                        op = nextarg("-");
                        if (!op) return l;
                }
                G.args++;
                r = eval4();
                val = arithmetic_common(l, r, op);
                freev(l);
                freev(r);
                l = int_value(val);
        }
}

/* Handle comparisons.  */

static VALUE *eval2(void)
{
        VALUE *l, *r;
        int op;
        arith_t val;

        l = eval3();
        while (1) {
                op = nextarg("<");
                if (!op) { op = nextarg("<=");
                 if (!op) { op = nextarg("=");
                  if (!op) { op = nextarg("==");
                   if (!op) { op = nextarg("!=");
                    if (!op) { op = nextarg(">=");
                     if (!op) { op = nextarg(">");
                      if (!op) return l;
                }}}}}}
                G.args++;
                r = eval3();
                toarith(l);
                toarith(r);
                val = cmp_common(l, r, op);
                freev(l);
                freev(r);
                l = int_value(val);
        }
}

/* Handle &.  */

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

        l = eval2();
        while (nextarg("&")) {
                G.args++;
                r = eval2();
                if (null(l) || null(r)) {
                        freev(l);
                        freev(r);
                        l = int_value(0);
                } else
                        freev(r);
        }
        return l;
}

/* Handle |.  */

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

        l = eval1();
        while (nextarg("|")) {
                G.args++;
                r = eval1();
                if (null(l)) {
                        freev(l);
                        l = r;
                } else
                        freev(r);
        }
        return l;
}

int expr_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int expr_main(int argc UNUSED_PARAM, char **argv)
{
        VALUE *v;

        INIT_G();

        xfunc_error_retval = 2; /* coreutils compat */
        G.args = argv + 1;
        if (*G.args == NULL) {
                bb_error_msg_and_die("too few arguments");
        }
        v = eval();
        if (*G.args)
                bb_error_msg_and_die("syntax error");
        if (v->type == INTEGER)
                printf("%" PF_REZ "d\n", PF_REZ_TYPE v->u.i);
        else
                puts(v->u.s);
        fflush_stdout_and_exit(null(v));
}