#include "icmp.h"
#include <cstring>
#include "eth.h"
#include "ipv4.h"
#include "parse_buffer.h"
#include "prepend_buffer.h"

namespace icmp {

void handle(std::span<const uint8_t> frame, span_writer& tx) {
    parse_buffer pb(frame);
    auto* eth_hdr = pb.consume<eth::header>();
    auto* ip = pb.consume<ipv4::header>();
    if (!ip) return;
    if (!ipv4::addressed_to_us(ip->dst)) return;

    size_t options_len = ip->header_len() - sizeof(ipv4::header);
    if (options_len > 0 && !pb.skip(options_len)) return;

    size_t icmp_len = ip->total() - ip->header_len();
    if (pb.remaining_size() < icmp_len) return;

    auto* icmp_pkt = pb.consume<echo>();
    if (!icmp_pkt) return;
    if (icmp_pkt->type != 8) return;

    prepend_buffer<4096> buf;
    memcpy(buf.append(icmp_len), pb.remaining().data() - sizeof(echo), icmp_len);

    auto* reply = reinterpret_cast<echo*>(buf.data());
    reply->type = 0;
    reply->checksum = 0;
    reply->checksum = ipv4::checksum(reply, icmp_len);

    ipv4::prepend(buf, eth_hdr->src, eth::get_mac(), ipv4::get_ip(), ip->src, 1, icmp_len);
    eth::send_raw(buf.span());
}

void init() {
    ipv4::register_protocol(1, handle);
}

bool parse_echo_reply(std::span<const uint8_t> frame, ipv4::ip4_addr& src_ip, uint16_t expected_id) {
    parse_buffer pb(frame);
    auto* eth_hdr = pb.consume<eth::header>();
    if (!eth_hdr) return false;
    if (eth_hdr->ethertype != eth::ETH_IPV4) return false;

    auto* ip = pb.consume<ipv4::header>();
    if (!ip) return false;
    if ((ip->ver_ihl >> 4) != 4) return false;
    if (ip->protocol != 1) return false;

    size_t options_len = ip->header_len() - sizeof(ipv4::header);
    if (options_len > 0 && !pb.skip(options_len)) return false;

    auto* icmp_pkt = pb.consume<echo>();
    if (!icmp_pkt) return false;
    if (icmp_pkt->type != 0) return false;
    if (icmp_pkt->id != expected_id) return false;

    src_ip = ip->src;
    return true;
}

} // namespace icmp