#include "internal/icmp_packet_internal.h"
#include "internal/icmp_packet.h"
#include "internal/icmp_utils.h"
#include <stddef.h>
#include <string.h>
#include <arpa/inet.h>

/* Forward declarations */
static void write_icmp_header(struct icmp_header *hdr, uint8_t type,
								uint8_t code, uint32_t header_rest);
/* -------------------- */

int
icmp_build_packet(void *buffer, size_t buffer_len, uint8_t type, uint8_t code,
					uint32_t header_rest, const void *payload,
					size_t payload_len)
{
	const size_t required_len = sizeof(struct icmp_header) + payload_len;

	if (buffer_len < required_len)
		return -1;

	struct icmp_header *h = (struct icmp_header *)buffer;

	write_icmp_header(h, type, code, header_rest);
	if (payload_len > 0)
		memcpy((uint8_t *)buffer + sizeof(struct icmp_header), payload,
				payload_len);

	h->checksum = htons(icmp_checksum(h, required_len));

	return (int)required_len;
}

static void
write_icmp_header(struct icmp_header *hdr, uint8_t type, uint8_t code,
					uint32_t header_rest)
{
	hdr->type = type;
	hdr->code = code;
	hdr->checksum = 0; // will be computed later
	hdr->un.gateway = header_rest;
}