#pragma once
#include <array>
#include <cstdint>
#include <functional>
#include <span>
#include "eth.h"
#include "span_writer.h"

namespace ipv4 {

using ip4_addr = std::array<uint8_t, 4>;

struct __attribute__((packed)) header {
    eth::header eth;
    uint8_t ver_ihl;
    uint8_t dscp_ecn;
    uint16_t total_len;
    uint16_t identification;
    uint16_t flags_frag;
    uint8_t ttl;
    uint8_t protocol;
    uint16_t checksum;
    ip4_addr src;
    ip4_addr dst;

    size_t ip_header_len() const { return (ver_ihl & 0x0F) * 4; }
    size_t ip_total_len() const { return __builtin_bswap16(total_len); }
    const uint8_t* ip_start() const { return reinterpret_cast<const uint8_t*>(&ver_ihl); }
    uint8_t* ip_start() { return reinterpret_cast<uint8_t*>(&ver_ihl); }
};
static_assert(sizeof(header) == 34);

struct __attribute__((packed)) udp_header {
    header ip;
    uint16_t src_port;
    uint16_t dst_port;
    uint16_t length;
    uint16_t checksum;
};
static_assert(sizeof(udp_header) == 42);

uint16_t checksum(const void* data, size_t len);

void handle(std::span<const uint8_t> frame, span_writer& tx,
            eth::mac_addr our_mac, ip4_addr our_ip, ip4_addr subnet_broadcast,
            std::function<void(std::span<const uint8_t>)> send_raw,
            std::function<void(std::span<const uint8_t>, span_writer&)> handle_udp);

} // namespace ipv4