#include <unistd.h>
#include <errno.h>
#include <limits.h>
#include <string.h>
#include "syscall.h"
#include "libc.h"

static char *do_getcwd(char *buf, size_t size)
{
	long ret = syscall(SYS_getcwd, buf, size);
	if (ret < 0)
		return 0;
	if (ret == 0 || buf[0] != '/') {
		errno = ENOENT;
		return 0;
	}
	return buf;
}

static char *getcwd_glibc(size_t size)
{
	char tmp[PATH_MAX];
	if (!do_getcwd(tmp, sizeof tmp))
		return 0;
	size_t len = strlen(tmp) + 1;
	if (!size)
		size = len;
	else if (size < len) {
		errno = ERANGE;
		return 0;
	}
	char *buf = malloc(size);
	if (!buf) {
		errno = ENOMEM;
		return 0;
	}
	memcpy(buf, tmp, len);
	return buf;
}

char *getcwd(char *buf, size_t size)
{
	if (!buf)
		return getcwd_glibc(size);
	if (!size) {
		errno = EINVAL;
		return 0;
	}
	return do_getcwd(buf, size);
}