package sdnotify

import (
	"fmt"
	"math"
	"net"
	"os"
	"strconv"
	"time"
)

const (
	SocketEnv       = "NOTIFY_SOCKET"
	WatchdogUsecEnv = "WATCHDOG_USEC"
	WatchdogPIDEnv  = "WATCHDOG_PID"
)

const (
	Ready    = "READY=1"
	Stopping = "STOPPING=1"
	Watchdog = "WATCHDOG=1"
)

func WatchdogInterval() (time.Duration, bool) {
	usec, err := strconv.ParseInt(os.Getenv(WatchdogUsecEnv), 10, 64)
	if err != nil || usec <= 0 || usec > math.MaxInt64/int64(time.Microsecond) {
		return 0, false
	}
	if pid := os.Getenv(WatchdogPIDEnv); pid != "" && pid != strconv.Itoa(os.Getpid()) {
		return 0, false
	}
	return time.Duration(usec) * time.Microsecond, true
}

func Notify(state string) error {
	name := os.Getenv(SocketEnv)
	if name == "" {
		return nil
	}
	if name[0] != '/' && name[0] != '@' {
		return fmt.Errorf("%s=%q is neither an absolute path nor an abstract socket (@name)", SocketEnv, name)
	}
	conn, err := net.DialUnix("unixgram", nil, &net.UnixAddr{Name: name, Net: "unixgram"})
	if err != nil {
		return fmt.Errorf("notify %s: %w", state, err)
	}
	defer conn.Close()
	if _, err := conn.Write([]byte(state)); err != nil {
		return fmt.Errorf("notify %s: %w", state, err)
	}
	return nil
}