#!/usr/bin/env bash

INTERVAL="1"  # update interval in seconds

# Network interface to monitor
network_name="en0"

if [[ $(uname -s) == "Darwin" ]]; then
    network_name="en0" # en0 is wifi, TODO: Update network_name
elif [[ $(uname -s) == "Linux" ]]; then
    network_name=$(tmux show-option -gqv "@dracula-network-bandwidth")
else
    # update this later for window
    echo "Unknown operating system"
    exit 1
fi

main() {
  while true
  do
    output_download=""
    output_upload=""
    output_download_unit=""
    output_upload_unit=""

    if [[ $(uname -s) == "Linux" ]]; then
      initial_download=$(cat /sys/class/net/"$network_name"/statistics/rx_bytes)
      initial_upload=$(cat /sys/class/net/"$network_name"/statistics/tx_bytes)

      sleep "$INTERVAL"

      final_download=$(cat /sys/class/net/"$network_name"/statistics/rx_bytes)
      final_upload=$(cat /sys/class/net/"$network_name"/statistics/tx_bytes)
    else
      initial_download=$(netstat -I "$network_name" -b | tail -n 1 | awk '{print $7}')
      initial_upload=$(netstat -I "$network_name" -b | tail -n 1 | awk '{print $10}')

      sleep $INTERVAL

      final_download=$(netstat -I "$network_name" -b | tail -n 1 | awk '{print $7}')
      final_upload=$(netstat -I "$network_name" -b | tail -n 1 | awk '{print $10}')
    fi

    total_download_bps=$(expr $final_download - $initial_download)
    total_upload_bps=$(expr $final_upload - $initial_upload)

    if [ $total_download_bps -gt 1073741824 ]; then
      output_download=$(echo "$total_download_bps 1024" | awk '{printf "%.2f \n", $1/($2 * $2 * $2)}')
      output_download_unit="gB/s"
    elif [ $total_download_bps -gt 1048576 ]; then
      output_download=$(echo "$total_download_bps 1024" | awk '{printf "%.2f \n", $1/($2 * $2)}')
      output_download_unit="mB/s"
    else
      output_download=$(echo "$total_download_bps 1024" | awk '{printf "%.2f \n", $1/$2}')
      output_download_unit="kB/s"
    fi

    if [ $total_upload_bps -gt 1073741824 ]; then
      output_upload=$(echo "$total_download_bps 1024" | awk '{printf "%.2f \n", $1/($2 * $2 * $2)}')
      output_upload_unit="gB/s"
    elif [ $total_upload_bps -gt 1048576 ]; then
      output_upload=$(echo "$total_upload_bps 1024" | awk '{printf "%.2f \n", $1/($2 * $2)}')
      output_upload_unit="mB/s"
    else
      output_upload=$(echo "$total_upload_bps 1024" | awk '{printf "%.2f \n", $1/$2}')
      output_upload_unit="kB/s"
    fi

    echo "↓ $output_download$output_download_unit • ↑ $output_upload$output_upload_unit"
  done
}
main