package main

// The machine's monotonic clock, shared by its processes: the night's process writes it beside its count and
// the health tool, in another process, reads it again (novox/hq issue 489). Go's own monotonic reading is
// only comparable within one process.

import (
	"os"
	"strings"
	"syscall"
	"time"
	"unsafe"
)

const bootID = "/proc/sys/kernel/random/boot_id"

// machineClock is this boot's id and CLOCK_MONOTONIC, which on Linux does not run while the machine is
// suspended and begins again at each boot; "" and 0 when either cannot be read.
func machineClock() (string, time.Duration) {
	raw, err := os.ReadFile(bootID)
	if err != nil {
		return "", 0
	}
	var ts syscall.Timespec
	const clockMonotonic = 1
	if _, _, e := syscall.Syscall(syscall.SYS_CLOCK_GETTIME, clockMonotonic, uintptr(unsafe.Pointer(&ts)), 0); e != 0 {
		return "", 0
	}
	return strings.TrimSpace(string(raw)), time.Duration(ts.Nano())
}