#!/bin/bash

# Set CPU usage we consider maximum, in % CPU utilisation
maxCpu=100

# Setup our levels list and idle level (0% specifically)
level=("012" "022" "021" "020" "120" "220" "210" "200")
idleLevel="002"

# Work out how many levels we have (level list length)
levels=${#level[@]}

# Check if we have any arguments
if [ $# -eq 0 ]; then
    # No arguments provided, display usage
    echo "Usage: $0 procname"
else
    # Arguments provided, run infinite loop observing process state
    while [ 1 ]; do
        # Read the process information
        stats=`ps -C "$1" -o %cpu | tail -n 1`      # Get the list of processes matching a name, show only CPU usage and trim to only the last line

        # Check if we got any matches
        if [[ $stats = "%CPU" ]]; then              # Note the double brackets '[[' and ']]' are needed for a literal match
            # Last line was the heading, this means no matches
            echo "000" > /dev/ledborg                   # Set LedBorg to off
        elif [[ $stats = " 0.0" ]]; then            # Note the double brackets '[[' and ']]' are needed for a literal match
            # We had a match, however no CPU activity above 0.1% seen, label as idle
            echo "$idleLevel" > /dev/ledborg            # Set colour to the idle value
        else
            # We had a match, pick a colour based on utilisation level
            cpuint=${stats/.*}                          # Truncate number to an integer
            util=$((($cpuint * $levels) / $maxCpu))     # Work out the slots as evenly spaced from 0% to maxCpu
            if [ $util -ge $levels ]; then              # Check if we have a slot which is too high (at >= maxCpu this will happen)
                util=$(($levels - 1))                       # Cap at highest slot
            fi
            echo ${level[$util]} > /dev/ledborg         # Set colour based on utilisation
        fi

        # Wait for a period
        sleep 1
    done
fi