#!/usr/bin/env bash

INTERVAL="1"  # update interval in seconds

network_name=$(tmux show-option -gqv "@tmux2k-network-bandwidth")

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

    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)

    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