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

#define ETH_UDP_HEADER_SIZE (8)

typedef struct {
    uint32_t sourceIpAddr;
    uint32_t destIpAddr;
    uint8_t zero;
    uint8_t protocol;
    uint16_t udpLength;
} UdpPseudoHeader;

static uint16_t udp_checksum(const UdpPseudoHeader * pseudoHeader, const uint8_t * headerPayload, uint32_t headerPayloadSize) {
    uint16_t chksum = 0;
    uint16_t i;

    // pseudoheader
    for (i = 0; i < sizeof(UdpPseudoHeader) / 2; i++) {
        chksum += ~((uint16_t *)pseudoHeader)[i];
    }

    // UDP header and payload
    for (i = 0; i < headerPayloadSize / 2; i++) {
        if (i != 3) { // skip Checksum field
            chksum += ~((uint16_t *) headerPayload)[i];
        }
    }

    // pad if packet size is odd
    chksum += ~((uint16_t)headerPayload[headerPayloadSize - 1] << 8);

    return chksum;
}

int parse_udp(const uint8_t *hdr, uint32_t size, PcktProps * props) {
    UdpProps * udpProps = (UdpProps *)props;
    FETCH_WORD_H2N_ADVANCE(&udpProps->SourcePort, hdr);
    FETCH_WORD_H2N_ADVANCE(&udpProps->DestinationPort, hdr);
    FETCH_WORD_H2N_ADVANCE(&udpProps->Length, hdr);
    FETCH_WORD_H2N_ADVANCE(&udpProps->Checksum, hdr);

    // common fields...
    udpProps->headerSize = ETH_UDP_HEADER_SIZE;
    udpProps->validityOK = size == udpProps->Length; // TODO UDP checksum validation!
    udpProps->containedPacketClass = 0;

    return udpProps->validityOK ? 0 : -1;
}

void insert_udp_header(uint8_t *hdr, const PcktHeaderElement *headers) {
    UdpProps * udpProps = (UdpProps *) &headers->props;
    FILL_WORD_H2N_ADVANCE(hdr, udpProps->SourcePort);
    FILL_WORD_H2N_ADVANCE(hdr, udpProps->DestinationPort);
    FILL_WORD_H2N_ADVANCE(hdr, udpProps->Length);

    // calculate checksum
    const IPv4Props * ipProps = (IPv4Props *)&headers->prev->props;
    UdpPseudoHeader ph = { ipProps->SourceIPAddr, ipProps->DestIPAddr, 0, ETH_UDP_PACKET_CLASS, udpProps->Length };
    udpProps->Checksum = udp_checksum(&ph, hdr, udpProps->Length);
    FILL_WORD_H2N_ADVANCE(hdr, udpProps->Checksum);
}