#include "internal/icmp_packet_internal.h"
#include "internal/icmp_packet.h"
#include <netinet/in.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>

/* Minimum IP header size */
#define MIN_IP_HEADER_SIZE 20

/* Forward declarations */
static int validate_ip_header(const struct ip_header *hdr, size_t buffer_len);
static size_t extract_ip_header_length(uint8_t version_ihl);
/* -------------------- */

int
icmp_parse_ip_header(const void *buffer, size_t buffer_len, uint8_t *ttl,
						struct in_addr *src_addr, size_t *ip_hdr_len,
						struct in_addr *dst_addr, uint8_t *protocol)
{
	const struct ip_header *h;
	size_t ihl_bytes;

	if (buffer_len < MIN_IP_HEADER_SIZE)
		return -1;

	h = (const struct ip_header *)buffer;
	ihl_bytes = extract_ip_header_length(h->version_ihl);

	if (0 != validate_ip_header(h, buffer_len))
		return -1;

	if (ttl)
		*ttl = h->ttl;
	if (src_addr)
		src_addr->s_addr = h->saddr;
	if (dst_addr)
		dst_addr->s_addr = h->daddr;
	if (protocol)
		*protocol = h->protocol;
	if (ip_hdr_len)
		*ip_hdr_len = ihl_bytes;

	return 0;
}

static int
validate_ip_header(const struct ip_header *hdr, size_t buffer_len)
{
	uint8_t ihl;
	size_t header_len;

	if (4 != (hdr->version_ihl >> 4))
		return -1;

	ihl = hdr->version_ihl & 0x0F;
	if (ihl < 5)
		return -1;

	header_len = (size_t)(ihl << 2);
	if (header_len > buffer_len)
		return -1;

	return 0;
}

static size_t
extract_ip_header_length(uint8_t version_ihl)
{
	return (size_t)((version_ihl & 0x0F) << 2);
}