/*
 * (C) Copyright 2016 Leo C. <erbl259-lmu@yahoo.de>
 *
 * SPDX-License-Identifier:	GPL-2.0
 */

#include "eval_arg.h"
#include "common.h"
#include <stdlib.h>
#include <ctype.h>
#include <setjmp.h>
#include "print-utils.h"
#include "command.h"	/* jump_buf */

static jmp_buf eval_jbuf;
static char ch;
static char *start_p;
static char *bp;


static long expr(void);

static void print_error_pos(void)
{
	printf_P(PSTR("Arg: '%s'\n"
	              "      "), start_p);
	print_blanks(bp - start_p);
	my_puts_P(PSTR("^syntax error!\n"));
}

static void error (void)
{
	--bp;
	longjmp (eval_jbuf, 1);
}

static void next(void)
{
	do
		ch = *bp++;
	while (isspace(ch));
}

static long number (void)
{
	int base = 16;
	char *end_p;
	long n;

	if (ch == '$') {					/* FIXME: should be '#' */
		next();
		base = 10;
	}
	if (!isdigit(ch) && !(base == 16 && isxdigit(ch)))
		error ();

	n = strtoul(bp - 1, &end_p, base);

	if (end_p == bp - 1)
		error();
	bp = end_p;
	next();

	return n;
}

static long factor (void)
{
	long f;

	if (ch == '(')
	{
		next();
		f = expr();
		if (ch == ')')
			next();
		else
			error ();
	} else {
		char sign = ch;
		if (sign == '+' || sign == '-') {
			next();
		}
		f = number();
		if (sign == '-')
			f = -f;
	}
	return f;
}

static long term (void)
{
	long t = factor();

	for (;;)
		switch (ch) {
		case '*':
			next();
			t *= factor();
			break;
		case '/':
			next();
			t /= factor();
			break;
		case '%':
			next();
			t %= factor();
			break;
		default:
			return t;
		}
}


static long expr(void)
{
	long e = term ();

	while (ch == '+' || ch == '-') {
		char op = ch;
		next();
		if (op == '-')
			e -= term ();
		else
			e += term ();
	}
	return e;
}

long eval_arg(char *arg, char **end_ptr)
{
	long val;

	start_p = arg;
	bp = arg;
	next();
	if (setjmp (eval_jbuf) != 0) {
		if (!end_ptr) {
			print_error_pos();
			longjmp(cmd_jbuf, 1);
		}
		val = -1;
	} else {
		val = expr ();
		--bp;
	}

	if (!end_ptr) {
		if (*bp != '\0') {
			print_error_pos();
			longjmp(cmd_jbuf, 1);
		}
	} else
		*end_ptr = bp;

	return val;
}