#!/bin/bash
# Emits {"cpu":<pct>} — CPU usage percent since the previous invocation.
# Deltas are computed against a cached state file, so this script must be
# polled periodically rather than run once.
set -uo pipefail

STATE_DIR="${XDG_CACHE_HOME:-$HOME/.cache}/omaspeedmeter"
STATE_FILE="$STATE_DIR/cpu"
mkdir -p -m 700 "$STATE_DIR"

prev_total=0
prev_idle=0
have_prev=0
if [[ -f "$STATE_FILE" ]]; then
    while IFS='=' read -r key value; do
        case "$key" in
        prev_total) [[ "$value" =~ ^[0-9]+$ ]] && prev_total="$value" && have_prev=1 ;;
        prev_idle) [[ "$value" =~ ^[0-9]+$ ]] && prev_idle="$value" ;;
        esac
    done <"$STATE_FILE"
fi

read -r _ cu cn cs ci ciow cirq csirq cst _ </proc/stat
cpu_idle=$((ci + ciow))
cpu_total=$((cu + cn + cs + ci + ciow + cirq + csirq + cst))

cpu_pct=0
if ((have_prev)); then
    d_total=$((cpu_total - prev_total))
    d_idle=$((cpu_idle - prev_idle))
    if ((d_total > 0)); then
        cpu_pct=$(awk -v dt="$d_total" -v di="$d_idle" 'BEGIN { p = (dt-di)/dt*100; if (p<0) p=0; if (p>100) p=100; printf "%.0f", p }')
    fi
fi

tmp_file=$(mktemp "$STATE_DIR/cpu.XXXXXX")
{
    echo "prev_total=$cpu_total"
    echo "prev_idle=$cpu_idle"
} >"$tmp_file"
mv -f "$tmp_file" "$STATE_FILE"

printf '{"cpu":%s}\n' "$cpu_pct"