//go:build darwin

package stats

import (
	"os/exec"
	"strconv"
	"strings"
)

func (r *Reporter) SystemCPUPercent() float64 {
	idle, total, ok := readDarwinCPUSample()
	if !ok {
		return 0
	}

	r.mu.Lock()
	defer r.mu.Unlock()

	if !r.hasSample {
		r.lastIdle = idle
		r.lastTotal = total
		r.hasSample = true
		return 0
	}

	idleDelta := float64(idle - r.lastIdle)
	totalDelta := float64(total - r.lastTotal)
	r.lastIdle = idle
	r.lastTotal = total

	return cpuBusyPercentFromDeltas(idleDelta, totalDelta)
}

func readDarwinCPUSample() (idle, total uint64, ok bool) {
	out, err := exec.Command("sysctl", "-n", "kern.cp_time").Output()
	if err != nil {
		return 0, 0, false
	}
	return parseDarwinCPTimes(string(out))
}

func parseDarwinCPTimes(raw string) (idle, total uint64, ok bool) {
	parts := strings.Fields(strings.TrimSpace(raw))
	if len(parts) < 4 {
		return 0, 0, false
	}
	var values []uint64
	for _, p := range parts {
		v, err := strconv.ParseUint(p, 10, 64)
		if err != nil {
			return 0, 0, false
		}
		values = append(values, v)
	}
	for _, v := range values {
		total += v
	}
	// user, nice, sys, idle[, intr]
	idle = values[3]
	return idle, total, true
}