/**
 * @file stdlib.c
 * Provides missing C standard library functions
 * The newlib versions of these calls are not being used due to dependence on
 * unsupported system calls.
 *
 * Copyright (C) 2018 Clyne Sullivan
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <stdlib.h>

#include <ctype.h>
#include <stdarg.h>
#include <string.h>

extern char *itoa(int, char *, int);

void _exit(int code)
{
	(void)code;
	for (;;);
}

char *snprintf(char *buf, unsigned int max, const char *format, ...)
{
	va_list args;
	va_start(args, format);

	if (buf == 0 || max == 0)
		return 0;

	static char nbuf[32];
	unsigned int off = 0;
	for (unsigned int i = 0; format[i] != '\0' && off < max; i++) {
		if (format[i] == '%') {
			i++;
			nbuf[0] = '\0';
			switch (format[i]) {
			case 'd':
				itoa(va_arg(args, int), nbuf, 10);
				break;
			case 'u':
				itoa(va_arg(args, unsigned int), nbuf, 10);
				break;
			case 'x':
			case 'p':
				itoa(va_arg(args, unsigned int), nbuf, 16);
				break;
			case 'f':
				itoa(va_arg(args, double), nbuf, 10);
				break;
			default:
				buf[off++] = format[i];
				nbuf[0] = '\0';
				break;
			}
			if (nbuf[0] != '\0') {
				for (unsigned int j = 0; off < max && j < 32 &&
					nbuf[j] != '\0'; off++, j++)
					buf[off] = nbuf[j];
			}
		} else {
			buf[off++] = format[i];
		}
	}


	buf[off >= max ? max - 1 : off] = '\0';
	va_end(args);
	return buf;
}

float strtof(const char *s, char **endptr)
{
	(void)endptr;

	float res = 0.0f;
	char neg = 0;
	unsigned int i = 0;

	if (s[0] == '-') {
		neg = 1;
		i++;
	}

	for (; isdigit(s[i]); i++) {
		res *= 10.0f;
		res += (s[i] - '0');
	}

	if (s[i] != '.')
		goto end;

	float div = 0.1f;
	for (i++; isdigit(s[i]); i++) {
		res += div * (s[i] - '0');
		div /= 10.0f;
	}

end:
	return (neg == 0) ? res : -res;
}

int atoi(const char *s)
{
	unsigned int i = 0;
	char neg = 0;
	int n = 0;

	if (s[0] == '-') {
		neg = 1;
		i = 1;
	}

	for (; isdigit(s[i]); i++) {
		n *= 10;
		n += s[i] - '0';
	}

	return (neg == 0) ? n : -n;
}

char *ftostr(char *buf, float f)
{
	if (buf == 0)
		return 0;

	if (f == 0) {
		buf[0] = '0';
		buf[1] = '\0';
		return buf;
	}

	unsigned int i = 0; // offset

	// strip decimals, convert in reverse
	for (int d = f; d != 0; d /= 10)
		buf[i++] = d % 10 + '0';

	// reverse
	for (unsigned int j = 0; j < i / 2; j++) {
		char c = buf[i - j - 1];
		buf[i - j - 1] = buf[j];
		buf[j] = c;
	}

	if ((float)((int)f) == f)
		goto end;

	buf[i++] = '.';

	// decimals
	float d = f;
	// precision of 5 is safe, more gets questionable
	for (unsigned int p = 0; p < 5; p++) {
		d *= 10;
		buf[i++] = (int)d % 10 + '0';
	}

	// trim 0's
	for (unsigned int j = i - 1; buf[j] == '0'; j--)
		buf[j] = '\0';
end:
	buf[i] = '\0';
	return buf;
}