#!/usr/bin/env bash
set -euo pipefail

iface="${POLYBAR_NETWORK:-eth0}"
state_dir="${XDG_RUNTIME_DIR:-/tmp}"
if [ ! -w "$state_dir" ]; then
  state_dir="${XDG_CACHE_HOME:-$HOME/.cache}"
  mkdir -p "$state_dir"
fi
if [ ! -w "$state_dir" ]; then
  state_dir="/tmp"
fi
state_file="$state_dir/polybar-net-${iface}.state"
rx_file="/sys/class/net/$iface/statistics/rx_bytes"
tx_file="/sys/class/net/$iface/statistics/tx_bytes"

human() {
  local bytes="$1"

  if [ "$bytes" -ge 1048576 ]; then
    awk -v v="$bytes" 'BEGIN { printf "%.1fM", v / 1048576 }'
  elif [ "$bytes" -ge 1024 ]; then
    awk -v v="$bytes" 'BEGIN { printf "%.0fK", v / 1024 }'
  else
    printf '%sB' "$bytes"
  fi
}

if [ ! -r "$rx_file" ] || [ ! -r "$tx_file" ]; then
  echo "n/a"
  exit 0
fi

now="$(date +%s)"
rx="$(cat "$rx_file")"
tx="$(cat "$tx_file")"

if [ -r "$state_file" ]; then
  read -r old_now old_rx old_tx <"$state_file" || true
else
  old_now="$now"
  old_rx="$rx"
  old_tx="$tx"
fi

printf '%s %s %s\n' "$now" "$rx" "$tx" >"$state_file"

delta=$((now - old_now))
if [ "$delta" -le 0 ]; then
  delta=1
fi

down=$(((rx - old_rx) / delta))
up=$(((tx - old_tx) / delta))

if [ "$down" -lt 0 ]; then
  down=0
fi

if [ "$up" -lt 0 ]; then
  up=0
fi

printf '%s/%s\n' "$(human "$down")" "$(human "$up")"