#!/usr/bin/env bash

#shows traffic on the specified device

while :; do
        function human_readable {
                VALUE=$1
                BIGGIFIERS=(B K M G)
                CURRENT_BIGGIFIER=0
                while [ $VALUE -gt 10000 ]; do
                        VALUE=$(($VALUE / 1000))
                        CURRENT_BIGGIFIER=$((CURRENT_BIGGIFIER + 1))
                done
                #echo "value: $VALUE"
                #echo "biggifier: ${BIGGIFIERS[$CURRENT_BIGGIFIER]}"
                echo "$VALUE${BIGGIFIERS[$CURRENT_BIGGIFIER]}"
        }

        ###CHECKS####

        DEVICE=$1
        IS_GOOD=0
        for GOOD_DEVICE in $(grep ":" /proc/net/dev | awk '{print $1}' | sed s/:.*//); do
                if [ "$DEVICE" = "$GOOD_DEVICE" ]; then
                        IS_GOOD=1
                        break
                fi
        done
        if [ $IS_GOOD -eq 0 ]; then
                echo "Device $DEVICE not found. Should be one of these:"
                grep ":" /proc/net/dev | awk '{print $1}' | sed s/:.*//
                exit 1
        fi

        ###REAL STUFF
        LINE=$(grep $1 /proc/net/dev | sed s/.*://)
        RECEIVED=$(echo $LINE | awk '{print $1}')
        TRANSMITTED=$(echo $LINE | awk '{print $9}')
        TOTAL=$(($RECEIVED + $TRANSMITTED))

        SLP=1
        sleep $SLP

        LINE=$(grep $1 /proc/net/dev | sed s/.*://)
        RECEIVED=$(echo $LINE | awk '{print $1}')
        TRANSMITTED=$(echo $LINE | awk '{print $9}')
        SPEED=$((($RECEIVED + $TRANSMITTED - $TOTAL) / $SLP))

        echo "Current speed: $(human_readable $SPEED)/s"
done