Simple script to check the battery in your server and notify you / turn it off

batchk.go

package main

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"golang.org/x/sys/unix"
	"io"
	"net/http"
	"os"
	"os/signal"
	"time"
)

const (
	checkBatteryIntervalSec = 60
	telegramApiTimeoutSec   = 10
	telegramBotChatId       = "12345678"
	telegramBotToken        = "123456:ABC-DEF1234ghIkl-zyx57W2v1u123ew11"
	powerOffAtBatteryLevel  = 20
)

type batteryStatus struct {
	level     int
	isPlugged bool
}

func main() {
	notifyChan := make(chan batteryStatus, 20)
	go startChecker(notifyChan)
	go startNotifier(notifyChan)

	quit := make(chan os.Signal, 2)
	signal.Notify(quit, unix.SIGINT, unix.SIGTERM)
	<-quit
	os.Exit(0)
}

func startChecker(notify chan<- batteryStatus) {
	fAdpOnline, err := os.OpenFile("/sys/class/power_supply/ADP0/online", os.O_RDONLY, os.ModePerm)
	if err != nil {
		panic(err)
	}
	fBatCapacity, err := os.OpenFile("/sys/class/power_supply/BAT0/capacity", os.O_RDONLY, os.ModePerm)
	if err != nil {
		panic(err)
	}

	prevLvlRange := (readLevel(fBatCapacity) + 1) / 10
	wasPlugged := readIsPlugged(fAdpOnline)
	for {
		time.Sleep(time.Second * checkBatteryIntervalSec)

		batLvl := readLevel(fBatCapacity)
		batLvlRange := (batLvl + 1) / 10
		isPlugged := readIsPlugged(fAdpOnline)

		if batLvl <= powerOffAtBatteryLevel {
			_ = unix.Reboot(unix.LINUX_REBOOT_CMD_POWER_OFF)
			os.Exit(0)
		}
		if isPlugged != wasPlugged || batLvlRange < prevLvlRange {
			fmt.Printf("NOTIFY | Battery Level: % 3d %% | Is Plugged? %s\n",
				batLvl, ternaryOp(isPlugged, "Yes", "No"))
			notify <- batteryStatus{
				level:     batLvl,
				isPlugged: isPlugged,
			}
		}

		prevLvlRange = batLvlRange
		wasPlugged = isPlugged
	}
}

func startNotifier(queue <-chan batteryStatus) {
	client := http.Client{Timeout: telegramApiTimeoutSec * time.Second}
	hostname, err := os.Hostname()
	if err != nil {
		hostname = "<unknown>"
	}

	for {
		status := <-queue

		msg, err := json.Marshal(map[string]string{
			"chat_id":    telegramBotChatId,
			"parse_mode": "HTML",
			"text":       composeNotificationText(status, hostname),
		})
		if err != nil {
			panic(err)
		}

		for i := time.Millisecond; ; i *= 5 {
			if i > 5*time.Minute {
				i = 5 * time.Minute
			}
			time.Sleep(i)

			resp, err := client.Post(
				"https://api.telegram.org/bot"+telegramBotToken+"/sendMessage",
				"application/json", bytes.NewReader(msg))
			if err != nil {
				_, _ = fmt.Fprintln(os.Stderr, "error sending notification:", err)
				continue
			}
			body, err := io.ReadAll(resp.Body)
			if err != nil {
				panic(err)
			}
			fmt.Println(string(body))
			_ = resp.Body.Close()

			if resp.StatusCode < 200 || resp.StatusCode >= 300 {
				_, _ = fmt.Fprintln(os.Stderr, "non-ok status returned by telegram api:", resp.Status)
				continue
			}
			break
		}
	}
}

func readLevel(f *os.File) int {
	buf := make([]byte, 3)
	bytesRead, err := f.ReadAt(buf, 0)
	if bytesRead < 1 {
		err = errors.New("no data found in battery capacity file")
	}
	if err != nil && err != io.EOF {
		panic(err)
	}
	return bytesToInt(buf[:bytesRead])
}

func readIsPlugged(f *os.File) bool {
	buf := make([]byte, 1)
	bytesRead, err := f.ReadAt(buf, 0)
	if bytesRead < 1 {
		err = errors.New("no data found in power adapter online file")
	}
	if err != nil {
		panic(err)
	}
	return (buf[0] - '0') != 0
}

func composeNotificationText(status batteryStatus, hostname string) string {
	return fmt.Sprintf("⚠️ Battery notification alert ⚠️\n\n"+
		"%s <b>Current level:</b> %d %%\n"+
		"%s <b>Is plugged?</b> %s\n"+
		"🖥 <b>Server:</b> %s\n"+
		"🕓 <b>Time:</b> %s",
		ternaryOp(status.level > 50, "🔋", "\U0001FAAB"), status.level,
		ternaryOp(status.isPlugged, "⚡️", "🔌"), ternaryOp(status.isPlugged, "Yes", "No"),
		hostname,
		time.Now().Format(time.DateTime))
}

func ternaryOp(cond bool, a, b any) any {
	if cond {
		return a
	}
	return b
}

func bytesToInt(data []byte) (i int) {
	for _, b := range data {
		if b < '0' || b > '9' {
			return
		}
		i = (i * 10) + int(b-'0')
	}
	return
}