#!/bin/bash

cache_vals(){
    echo "$1" > "$3"
    echo -n "$2" >> "$3"
}

cached_eval(){
    local dir
    local a0
    local t0
    local a1
    local t1
    dir="/tmp/tmux_cpu_perc"
    a1="$1"
    t1="$2"
    if [ -f "$dir" ]; then
        a0="$(head -n1 "$dir")"
        t0="$(tail -n+2 "$dir")"
        cache_vals "$a1" "$t1" "$dir"
        awk -v a1="$a1" \
            -v t1="$t1" \
            -v a0="$a0" \
            -v t0="$t0" \
            'BEGIN {print 100*(a1-a0)/(t1-t0)}'
    else
        cache_vals "$a1" "$t1" "$dir"
        echo -n 0
    fi
}

get_cpu(){
    grep 'cpu ' /proc/stat | \
        awk '{a=($2+$4)}; {t=($2+$4+$5)} END {printf("%s %s", a, t)}'
}

cpu_percentage_format="%.2f%%"

cached_eval $(get_cpu) \
    | awk -v f="$cpu_percentage_format" \
          '{usage=$NF} END {printf(f, usage)}'