#include <stdbool.h>
#include "udp_packet.h"
#include "../../utils.h"
#include "ipv4_packet.h"
#include "ethernet_frame.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 * hdr, uint32_t size) {
    uint32_t sum = chksum((const uint8_t *)pseudoHeader, sizeof(UdpPseudoHeader)) + chksum(hdr, size);
    while (sum >> 16) {
        sum = (sum & 0xFFFF) + (sum >> 16);
    }
    return sum;
}

int parse_udp(const uint8_t *hdr, uint32_t size, PcktHeaderElement *pcktHdrLe, struct EthInterface_ *intf) {
    UdpProps *udpProps = HEADER_FETCH_PROPS(UdpProps, pcktHdrLe);
    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) {
    uint8_t *hdrBegin = hdr;
    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);
    uint8_t *ChkSumPtr = hdr;
    udpProps->Checksum = 0;
    FILL_WORD_H2N_ADVANCE(hdr, udpProps->Checksum);

    // calculate checksum
    const IPv4Props *ipProps = (IPv4Props *) &headers->prev->props;
    UdpPseudoHeader ph = {ipProps->SourceIPAddr, ipProps->DestIPAddr, 0, ETH_UDP_PACKET_CLASS, htons(udpProps->Length)};
    udpProps->Checksum = udp_checksum(&ph, hdrBegin, udpProps->Length);
    memcpy(ChkSumPtr, &udpProps->Checksum, 2);
}