#include <dirent.h>
#include <net/if.h>
#include <stdlib.h>
#include <string.h>

static int selector(const dirent* dirent)
{
	if (strcmp(dirent->d_name, "lo") == 0)
		return 1;
	if (strncmp(dirent->d_name, "eth", 3) == 0)
		return 1;
	return 0;
}

static int comparator(const dirent** d1, const dirent** d2)
{
	if (strcmp((*d1)->d_name, "lo"))
		return -1;
	if (strcmp((*d2)->d_name, "lo"))
		return +1;
	return alphasort(d1, d2);
}

char* if_indextoname(unsigned ifindex, char* ifname)
{
	if (ifindex == 0)
		return nullptr;

	dirent** namelist;

	const int count = scandir("/dev", &namelist, selector, comparator);
	if (count == -1)
		return nullptr;

	char* result = nullptr;
	if (ifindex - 1 < static_cast<unsigned>(count))
	{
		strcpy(ifname, namelist[ifindex - 1]->d_name);
		result = ifname;
	}

	for (int i = 0; i < count; i++)
		free(namelist[i]);
	free(namelist);

	return result;
}

unsigned if_nametoindex(const char* ifname)
{
	dirent** namelist;

	const int count = scandir("/dev", &namelist, selector, comparator);
	if (count == -1)
		return 0;

	unsigned result = 0;
	for (int i = 0; i < count; i++)
	{
		if (strcmp(ifname, namelist[i]->d_name) != 0)
			continue;
		result = i + 1;
		break;
	}

	for (int i = 0; i < count; i++)
		free(namelist[i]);
	free(namelist);

	return result;
}

struct if_nameindex* if_nameindex(void)
{
	dirent** namelist;

	const int count = scandir("/dev", &namelist, selector, comparator);
	if (count == -1)
		return nullptr;

	auto* result = static_cast<struct if_nameindex*>(malloc(sizeof(struct if_nameindex) * (count + 1)));
	if (result == nullptr)
		goto cleanup;

	for (unsigned i = 0; i < static_cast<unsigned>(count); i++)
	{
		auto* if_name = strdup(namelist[i]->d_name);
		if (if_name == nullptr)
		{
			if_freenameindex(result);
			result = nullptr;
			goto cleanup;
		}

		result[i] = {
			.if_index = i,
			.if_name = if_name,
		};
	}

	result[count] = {
		.if_index = 0,
		.if_name = nullptr,
	};

cleanup:
	for (int i = 0; i < count; i++)
		free(namelist[i]);
	free(namelist);

	return result;
}

void if_freenameindex(struct if_nameindex* ptr)
{
	for (auto* entry = ptr; entry->if_name; entry++)
		free(entry->if_name);
	free(ptr);
}