#define _GNU_SOURCE
#include <stdio.h>
#include <stdbool.h>
#include <unistd.h>
#include "icmp_server.h"
#include "util.h"


static const uint8_t* detect_payload(const uint8_t *data, size_t length) {
	// Detects the 16-byte "padding" payload one can send using the ping(1) utility.
	// This payload starts at byte 16 and repeats thereafter.
	if (length < 32) return NULL;

	// For each byte in the padding
	for (size_t i = 0; i < 16; i++) {
		// For each repetition
		for (size_t j = 1; 16 + 16 * j + i < length; j++) {
			// Assert that the padding indeed repeats
			if (data[16 + i] != data[16 + 16 * j + i]) return NULL;
		}
	}

	return data + 16;
}

int main() {
	int sock = icmp_server_open_socket();
	if (sock < 0) {
		perror("socket (icmp_server_open_socket)");
		return 1;
	}

	while (true) {
		struct icmp_incoming pkt = icmp_server_receive(sock);
		if (pkt.data == NULL) {
			perror("recvmsg (icmp_server_receive)");
			usleep(500000);
			continue;
		}
		// xxd(stderr, pkt.data, pkt.length);

		const uint8_t *payload = detect_payload(pkt.data, pkt.length);

		if (payload != NULL) {
			printf("payl");
			fwrite(&pkt.source_addr, 1, 4, stdout);
			fwrite(payload, 1, 16, stdout);
			fflush(stdout);
			uint16_t new_seqnum;
			if (readall(STDIN_FILENO, &new_seqnum, 2) < 0) {
				perror("read");
				new_seqnum = pkt.seqnum;
			}
			pkt.seqnum = new_seqnum;
		} else {
			fprintf(stderr, "Echoing packet due to invalid payload\n");
		}

		int ret = icmp_server_send_reply(sock, pkt.source_addr, pkt.id, pkt.seqnum, pkt.data, pkt.length);
		if (ret < 0) {
			perror("sendto (icmp_server_send_reply)");
			usleep(500000);
			continue;
		}
	}
}