//
// Created by epagris on 2022.11.03..
//

#include <stdbool.h>
#include "ethernet_frame.h"
#include "ipv4_packet.h"
#include "../../utils.h"

#include "../../eth_interface.h"

#define ETH_IP_HEADER_LENGTH (20)

static bool check_ipv4_validity(const uint8_t * hdr, const IPv4Props *ipProps) {
    bool valid =
            (ipProps->Version == 4) &&
            (ipProps->IHL == (ETH_IP_HEADER_LENGTH / 4)) &&
            (ntohs(ipProps->HeaderChecksum) == chksum(hdr, ETH_IPv4_HEADER_SIZE));
    return valid;
}

int parse_ipv4(const uint8_t *hdr, uint32_t size, PcktHeaderElement *pcktHdrLe, struct EthInterface_ *intf) {
    const uint8_t * hdrBegin = hdr;
    IPv4Props *ipProps = HEADER_FETCH_PROPS(IPv4Props, pcktHdrLe);
    uint8_t version_length;
    FETCH_ADVANCE(&version_length, hdr, 1);
    ipProps->Version = (version_length) >> 4;
    ipProps->IHL = (version_length) & 0x0F;
    FETCH_ADVANCE(&ipProps->DSF, hdr, 1);
    FETCH_WORD_H2N_ADVANCE(&ipProps->TotalLength, hdr);
    FETCH_WORD_H2N_ADVANCE(&ipProps->Identification, hdr);
    uint16_t flags_fragOffset;
    FETCH_WORD_H2N_ADVANCE(&flags_fragOffset, hdr);
    ipProps->Flags = (flags_fragOffset >> 13) & 0x07;
    ipProps->FragmentOffset = (flags_fragOffset & ~(0x07 << 13));
    FETCH_ADVANCE(&ipProps->TTL, hdr, 1);
    FETCH_ADVANCE(&ipProps->Protocol, hdr, 1);
    FETCH_WORD_H2N_ADVANCE(&ipProps->HeaderChecksum, hdr);
    FETCH_ADVANCE(&ipProps->SourceIPAddr, hdr, 4); // NO network -> host byte order conversion!
    FETCH_ADVANCE(&ipProps->DestIPAddr, hdr, 4);

    // fill-in common packet header fields
    ipProps->validityOK = check_ipv4_validity(hdrBegin, ipProps);
    ipProps->containedPacketClass = ipProps->Protocol;
    ipProps->headerSize = ETH_IP_HEADER_LENGTH;

    // if packet is valid, learn MAC-IP mapping
    if (ipProps->validityOK) {
        EthernetProps * ethProps = HEADER_FETCH_PROPS(EthernetProps, pcktHdrLe->prev); // fetch Ethernet header
        ArpEntry entry; // fill entry
        memcpy(&entry.eth, ethProps->sourceAddr, ETH_HW_ADDR_LEN);
        entry.ip = ipProps->SourceIPAddr;
        arpc_learn(intf->arpc, &entry); // learn new assignment
    }

    return ipProps->validityOK ? ipProps->Protocol : -1;
}

static uint16_t nextIpIdentification = 0;

void insert_ipv4_header(uint8_t *hdr, const PcktHeaderElement *headers) {
    uint8_t * hdrOrig = hdr;
    IPv4Props *ipProps = (IPv4Props *) &headers->props;
    ipProps->Identification = nextIpIdentification++; // auto-insert identification
    uint8_t version_length = (ipProps->Version << 4) | (ipProps->IHL & 0x0F);
    FILL_ADVANCE(hdr, &version_length, 1);
    FILL_ADVANCE(hdr, &ipProps->DSF, 1);
    FILL_WORD_H2N_ADVANCE(hdr, ipProps->TotalLength);
    FILL_WORD_H2N_ADVANCE(hdr, ipProps->Identification);
    uint16_t flags_fragOffset = ((ipProps->Flags & 0x07) << 13) | (ipProps->FragmentOffset & ~(0x07 << 13));
    FILL_WORD_H2N_ADVANCE(hdr, flags_fragOffset); // TODO...
    FILL_ADVANCE(hdr, &ipProps->TTL, 1);
    FILL_ADVANCE(hdr, &ipProps->Protocol, 1);
    uint8_t * ChkSumPtr = hdr;
    FILL_WORD_H2N_ADVANCE(hdr, 0x0000);
    FILL_ADVANCE(hdr, &ipProps->SourceIPAddr, 4);
    FILL_ADVANCE(hdr, &ipProps->DestIPAddr, 4);

    // calculate checksum after filling header
    ipProps->HeaderChecksum = chksum(hdrOrig, ETH_IPv4_HEADER_SIZE);
    memcpy(ChkSumPtr, &ipProps->HeaderChecksum, 2);
}

void ethmc_from_ipmc(uint8_t *hwa, ip4_addr ipa) {
    memcpy(hwa, ETH_ETHERNET_IPMC_HWADDR, ETH_HW_ADDR_LEN);
    const uint8_t * ipab = (const uint8_t *) &ipa;
    hwa[3] = (hwa[3] & 0x80) | (ipab[1] & 0x7F);
    hwa[4] = ipab[2];
    hwa[5] = ipab[3];
}