/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1993
 *	The Regents of the University of California.  All rights reserved.
 * Copyright (c) 2007
 *	Herbert Xu <herbert@gondor.apana.org.au>.  All rights reserved.
 * Copyright (c) 2026 Project Tick. All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Kenneth Almquist.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <limits.h>
#include <errno.h>
#include <inttypes.h>
#include <stdlib.h>
#include <stdio.h>
#include "arith.h"
#include "arith_yacc.h"
#include "expand.h"
#include "shell.h"
#include "error.h"
#include "memalloc.h"
#include "output.h"
#include "options.h"
#include "var.h"

#if ARITH_BOR + 11 != ARITH_BORASS || ARITH_ASS + 11 != ARITH_EQ
#error Arithmetic tokens are out of order.
#endif

static const char *arith_startbuf;

const char *arith_buf;
union yystype yylval;

static int last_token;

#define ARITH_PRECEDENCE(op, prec) [op - ARITH_BINOP_MIN] = prec

static const char prec[ARITH_BINOP_MAX - ARITH_BINOP_MIN] = {
	ARITH_PRECEDENCE(ARITH_MUL, 0),
	ARITH_PRECEDENCE(ARITH_DIV, 0),
	ARITH_PRECEDENCE(ARITH_REM, 0),
	ARITH_PRECEDENCE(ARITH_ADD, 1),
	ARITH_PRECEDENCE(ARITH_SUB, 1),
	ARITH_PRECEDENCE(ARITH_LSHIFT, 2),
	ARITH_PRECEDENCE(ARITH_RSHIFT, 2),
	ARITH_PRECEDENCE(ARITH_LT, 3),
	ARITH_PRECEDENCE(ARITH_LE, 3),
	ARITH_PRECEDENCE(ARITH_GT, 3),
	ARITH_PRECEDENCE(ARITH_GE, 3),
	ARITH_PRECEDENCE(ARITH_EQ, 4),
	ARITH_PRECEDENCE(ARITH_NE, 4),
	ARITH_PRECEDENCE(ARITH_BAND, 5),
	ARITH_PRECEDENCE(ARITH_BXOR, 6),
	ARITH_PRECEDENCE(ARITH_BOR, 7),
};

#define ARITH_MAX_PREC 8

int letcmd(int, char **);

static __dead2 void yyerror(const char *s)
{
	error("arithmetic expression: %s: \"%s\"", s, arith_startbuf);
	/* NOTREACHED */
}

static arith_t arith_lookupvarint(char *varname)
{
	const char *str;
	char *p;
	arith_t result;

	str = lookupvar(varname);
	if (uflag && str == NULL)
		yyerror("variable not set");
	if (str == NULL || *str == '\0')
		str = "0";
	errno = 0;
	result = strtoarith_t(str, &p);
	if (errno != 0 || *p != '\0')
		yyerror("variable conversion error");
	return result;
}

static inline int arith_prec(int op)
{
	return prec[op - ARITH_BINOP_MIN];
}

static inline int higher_prec(int op1, int op2)
{
	return arith_prec(op1) < arith_prec(op2);
}

static arith_t do_binop(int op, arith_t a, arith_t b)
{

	switch (op) {
	default:
	case ARITH_REM:
	case ARITH_DIV:
		if (!b)
			yyerror("division by zero");
		if (a == ARITH_MIN && b == -1)
			yyerror("divide error");
		return op == ARITH_REM ? a % b : a / b;
	case ARITH_MUL:
		return (uintmax_t)a * (uintmax_t)b;
	case ARITH_ADD:
		return (uintmax_t)a + (uintmax_t)b;
	case ARITH_SUB:
		return (uintmax_t)a - (uintmax_t)b;
	case ARITH_LSHIFT:
		return (uintmax_t)a << (b & (sizeof(uintmax_t) * CHAR_BIT - 1));
	case ARITH_RSHIFT:
		return a >> (b & (sizeof(uintmax_t) * CHAR_BIT - 1));
	case ARITH_LT:
		return a < b;
	case ARITH_LE:
		return a <= b;
	case ARITH_GT:
		return a > b;
	case ARITH_GE:
		return a >= b;
	case ARITH_EQ:
		return a == b;
	case ARITH_NE:
		return a != b;
	case ARITH_BAND:
		return a & b;
	case ARITH_BXOR:
		return a ^ b;
	case ARITH_BOR:
		return a | b;
	}
}

static arith_t assignment(int var, int noeval);

static arith_t primary(int token, union yystype *val, int op, int noeval)
{
	arith_t result;

again:
	switch (token) {
	case ARITH_LPAREN:
		result = assignment(op, noeval);
		if (last_token != ARITH_RPAREN)
			yyerror("expecting ')'");
		last_token = yylex();
		return result;
	case ARITH_NUM:
		last_token = op;
		return val->val;
	case ARITH_VAR:
		last_token = op;
		return noeval ? val->val : arith_lookupvarint(val->name);
	case ARITH_ADD:
		token = op;
		*val = yylval;
		op = yylex();
		goto again;
	case ARITH_SUB:
		*val = yylval;
		return -primary(op, val, yylex(), noeval);
	case ARITH_NOT:
		*val = yylval;
		return !primary(op, val, yylex(), noeval);
	case ARITH_BNOT:
		*val = yylval;
		return ~primary(op, val, yylex(), noeval);
	default:
		yyerror("expecting primary");
	}
}

static arith_t binop2(arith_t a, int op, int precedence, int noeval)
{
	for (;;) {
		union yystype val;
		arith_t b;
		int op2;
		int token;

		token = yylex();
		val = yylval;

		b = primary(token, &val, yylex(), noeval);

		op2 = last_token;
		if (op2 >= ARITH_BINOP_MIN && op2 < ARITH_BINOP_MAX &&
		    higher_prec(op2, op)) {
			b = binop2(b, op2, arith_prec(op), noeval);
			op2 = last_token;
		}

		a = noeval ? b : do_binop(op, a, b);

		if (op2 < ARITH_BINOP_MIN || op2 >= ARITH_BINOP_MAX ||
		    arith_prec(op2) >= precedence)
			return a;

		op = op2;
	}
}

static arith_t binop(int token, union yystype *val, int op, int noeval)
{
	arith_t a = primary(token, val, op, noeval);

	op = last_token;
	if (op < ARITH_BINOP_MIN || op >= ARITH_BINOP_MAX)
		return a;

	return binop2(a, op, ARITH_MAX_PREC, noeval);
}

static arith_t and(int token, union yystype *val, int op, int noeval)
{
	arith_t a = binop(token, val, op, noeval);
	arith_t b;

	op = last_token;
	if (op != ARITH_AND)
		return a;

	token = yylex();
	*val = yylval;

	b = and(token, val, yylex(), noeval | !a);

	return a && b;
}

static arith_t or(int token, union yystype *val, int op, int noeval)
{
	arith_t a = and(token, val, op, noeval);
	arith_t b;

	op = last_token;
	if (op != ARITH_OR)
		return a;

	token = yylex();
	*val = yylval;

	b = or(token, val, yylex(), noeval | !!a);

	return a || b;
}

static arith_t cond(int token, union yystype *val, int op, int noeval)
{
	arith_t a = or(token, val, op, noeval);
	arith_t b;
	arith_t c;

	if (last_token != ARITH_QMARK)
		return a;

	b = assignment(yylex(), noeval | !a);

	if (last_token != ARITH_COLON)
		yyerror("expecting ':'");

	token = yylex();
	*val = yylval;

	c = cond(token, val, yylex(), noeval | !!a);

	return a ? b : c;
}

static arith_t assignment(int var, int noeval)
{
	union yystype val = yylval;
	int op = yylex();
	arith_t result;
	char sresult[DIGITS(result) + 1];

	if (var != ARITH_VAR)
		return cond(var, &val, op, noeval);

	if (op != ARITH_ASS && (op < ARITH_ASS_MIN || op >= ARITH_ASS_MAX))
		return cond(var, &val, op, noeval);

	result = assignment(yylex(), noeval);
	if (noeval)
		return result;

	if (op != ARITH_ASS)
		result = do_binop(op - 11, arith_lookupvarint(val.name), result);
	snprintf(sresult, sizeof(sresult), ARITH_FORMAT_STR, result);
	setvar(val.name, sresult, 0);
	return result;
}

arith_t arith(const char *s)
{
	struct stackmark smark;
	arith_t result;

	setstackmark(&smark);

	arith_buf = arith_startbuf = s;

	result = assignment(yylex(), 0);

	if (last_token)
		yyerror("expecting EOF");

	popstackmark(&smark);

	return result;
}

/*
 *  The exp(1) builtin.
 */
int
letcmd(int argc, char **argv)
{
	const char *p;
	char *concat;
	char **ap;
	arith_t i;

	if (argc > 1) {
		p = argv[1];
		if (argc > 2) {
			/*
			 * Concatenate arguments.
			 */
			STARTSTACKSTR(concat);
			ap = argv + 2;
			for (;;) {
				while (*p)
					STPUTC(*p++, concat);
				if ((p = *ap++) == NULL)
					break;
				STPUTC(' ', concat);
			}
			STPUTC('\0', concat);
			p = grabstackstr(concat);
		}
	} else
		p = "";

	i = arith(p);

	out1fmt(ARITH_FORMAT_STR "\n", i);
	return !i;
}
