#!/bin/bash

# Function to print IP header
print_ip_header() {
    local iphdr="$1"
    local iphdrlen=$(($(($(($(printf "%d" "'${iphdr:0:1}")) & 0x0F)) * 4)))
    local src_ip="$(printf "%d.%d.%d.%d" "'${iphdr:12:1}" "'${iphdr:13:1}" "'${iphdr:14:1}" "'${iphdr:15:1}")"
    local dst_ip="$(printf "%d.%d.%d.%d" "'${iphdr:16:1}" "'${iphdr:17:1}" "'${iphdr:18:1}" "'${iphdr:19:1}")"

    printf "\nIP Header\n"
    printf "   |-IP Version        : %d\n" "$((($(printf "%d" "'${iphdr:0:1}")) >> 4))"
    printf "   |-IP Header Length  : %d DWORDS or %d Bytes\n" "$((($(printf "%d" "'${iphdr:0:1}")) & 0x0F))" "$iphdrlen"
    printf "   |-Type Of Service   : %d\n" "$(printf "%d" "'${iphdr:1:1}")"
    printf "   |-IP Total Length   : %d  Bytes(Size of Packet)\n" "$((($(printf "%d" "'${iphdr:2:1}") << 8) + $(printf "%d" "'${iphdr:3:1}")))"
    printf "   |-Identification    : %d\n" "$((($(printf "%d" "'${iphdr:4:1}") << 8) + $(printf "%d" "'${iphdr:5:1}")))"
    printf "   |-TTL               : %d\n" "$(printf "%d" "'${iphdr:8:1}")"
    printf "   |-Protocol          : %d\n" "$(printf "%d" "'${iphdr:9:1}")"
    printf "   |-Checksum          : %d\n" "$((($(printf "%d" "'${iphdr:10:1}") << 8) + $(printf "%d" "'${iphdr:11:1}")))"
    printf "   |-Source IP         : %s\n" "$src_ip"
    printf "   |-Destination IP    : %s\n" "$dst_ip"
}

# Function to print TCP header
print_tcp_packet() {
    local tcp_hdr="$1"
    local src_port="$((($(printf "%d" "'${tcp_hdr:0:1}") << 8) + $(printf "%d" "'${tcp_hdr:1:1}")))"
    local dst_port="$((($(printf "%d" "'${tcp_hdr:2:1}") << 8) + $(printf "%d" "'${tcp_hdr:3:1}")))"
    local seq_num="$((($(($(($(printf "%d" "'${tcp_hdr:4:1}")) << 24)) + ($(($(printf "%d" "'${tcp_hdr:5:1}")) << 16))) + ($(($(printf "%d" "'${tcp_hdr:6:1}")) << 8)) + $(printf "%d" "'${tcp_hdr:7:1}")))"
    local ack_num="$((($(($(($(printf "%d" "'${tcp_hdr:8:1}")) << 24)) + ($(($(printf "%d" "'${tcp_hdr:9:1}")) << 16))) + ($(($(printf "%d" "'${tcp_hdr:10:1}")) << 8)) + $(printf "%d" "'${tcp_hdr:11:1}")))"
    local header_len=$((($(printf "%d" "'${tcp_hdr:12:1}") >> 4) * 4))

    printf "\n\n***********************TCP Packet*************************\n"
    print_ip_header "$2"
    printf "\nTCP Header\n"
    printf "   |-Source Port      : %d\n" "$src_port"
    printf "   |-Destination Port : %d\n" "$dst_port"
    printf "   |-Sequence Number  : %u\n" "$seq_num"
    printf "   |-Acknowledge Number : %u\n" "$ack_num"
    printf "   |-Header Length    : %d DWORDS or %d BYTES\n" "$((($(printf "%d" "'${tcp_hdr:12:1}") >> 4) & 0x0F))" "$header_len"
    printf "   |-Urgent Flag      : %d\n" "$((($(printf "%d" "'${tcp_hdr:13:1}") & 0x20) >> 5))"
    printf "   |-Acknowledgement Flag : %d\n" "$((($(printf "%d" "'${tcp_hdr:13:1}") & 0x10) >> 4))"
    printf "   |-Push Flag        : %d\n" "$((($(printf "%d" "'${tcp_hdr:13:1}") & 0x08) >> 3))"
    printf "   |-Reset Flag       : %d\n" "$((($(printf "%d" "'${tcp_hdr:13:1}") & 0x04) >> 2))"
    printf "   |-Synchronise Flag : %d\n" "$((($(printf "%d" "'${tcp_hdr:13:1}") & 0x02) >> 1))"
    printf "   |-Finish Flag      : %d\n" "$((($(printf "%d" "'${tcp_hdr:13:1}") & 0x01)))"
    printf "   |-Window           : %d\n" "$((($(printf "%d" "'${tcp_hdr:14:1}") << 8) + $(printf "%d" "'${tcp_hdr:15:1}")))"
    printf "   |-Checksum         : %d\n" "$((($(printf "%d" "'${tcp_hdr:16:1}") << 8) + $(printf "%d" "'${tcp_hdr:17:1}")))"
    printf "   |-Urgent Pointer   : %d\n" "$((($(printf "%d" "'${tcp_hdr:18:1}") << 8) + $(printf "%d" "'${tcp_hdr:19:1}")))"
    printf "\n"
    printf "                        DATA Dump                         \n"
    printf "\nIP Header\n"
    printf "%s\n" "$2" | xxd -p -c $header_len
    printf "\nTCP Header\n"
    printf "%s\n" "${tcp_hdr:0:$header_len*2}" | xxd -p -c $header_len
    printf "\nData Payload\n"
    printf "%s\n" "${2:$header_len*2}"
    printf "\n###########################################################\n"
}

# Start tcpdump to capture packets
tcpdump -n -l |
# Process each line of tcpdump output
while read -r line; do
    # Extract protocol, source IP, destination IP, and TCP header
    protocol=$(awk '{print $2}' <<< "$line")
    src_ip=$(awk '{print $3}' <<< "$line" | awk -F. '{print $1"."$2"."$3"."$4}')
    dst_ip=$(awk '{print $5}' <<< "$line" | awk -F. '{print $1"."$2"."$3"."$4}')
    tcp_hdr=$(awk '{print $10}' <<< "$line")

    # Check if the line contains TCP header information
    if [[ "$protocol" == "TCP" && -n "$tcp_hdr" ]]; then
        # Call function to print TCP packet details
        print_tcp_packet "$tcp_hdr" "$line"
    fi
done