// Package daemon provides utilities for daemons.
package daemon

import "io"
import "os"
import "syscall"
import "strconv"
import "os/signal"

// PidFile is a string that contains a path to a pidfile.
type PidFile string

// Start writes to the pidfile.
func (pidfile PidFile) Start () error {
	return os.WriteFile(string(pidfile), []byte(strconv.Itoa(os.Getpid())), 0644)
}

// Close deletes the pidfile.
func (pidfile PidFile) Close () error {
	return os.Remove(string(pidfile))
}

// Empty returns true if the object is zero value (an empty string).
func (pidfile PidFile) Empty () bool {
	return pidfile == ""
}

// OnSigint calls the specified function once sigint is recieved. This function
// does not block, and spawns a goroutine that waits. For this reason, the
// callback must be safe to call concurrently.
func OnSigint (callback func ()) {
	go func () {
		sigintNotify := make(chan os.Signal, 1)
		signal.Notify(sigintNotify, os.Interrupt, syscall.SIGTERM)

		<-sigintNotify
		callback()
	} ()
}

// CloseOnSigint is like OnSigint, but takes an io.Closer.
func CloseOnSigint (closer io.Closer) {
	OnSigint(func () { closer.Close() })
}

// ShutdownOnSigint is like OnSigint, but takes an object with a Shutdown()
// method.
func ShutdownOnSigint (shutdowner interface { Shutdown() error }) {
	OnSigint(func () { shutdowner.Shutdown() })
}