package tcp

import (
	"net"
	"os"
	"strings"
	"syscall"

	reuseport "github.com/jbenet/go-reuseport"
)

// envReuseport is the env variable name used to turn off reuse port.
// It default to true.
const envReuseport = "IPFS_REUSEPORT"

// envReuseportVal stores the value of envReuseport. defaults to true.
var envReuseportVal = true

func init() {
	v := strings.ToLower(os.Getenv(envReuseport))
	if v == "false" || v == "f" || v == "0" {
		envReuseportVal = false
		log.Infof("REUSEPORT disabled (IPFS_REUSEPORT=%s)", v)
	}
}

// reuseportIsAvailable returns whether reuseport is available to be used. This
// is here because we want to be able to turn reuseport on and off selectively.
// For now we use an ENV variable, as this handles our pressing need:
//
//   IPFS_REUSEPORT=false ipfs daemon
//
// If this becomes a sought after feature, we could add this to the config.
// In the end, reuseport is a stop-gap.
func ReuseportIsAvailable() bool {
	return envReuseportVal && reuseport.Available()
}

// ReuseErrShouldRetry diagnoses whether to retry after a reuse error.
// if we failed to bind, we should retry. if bind worked and this is a
// real dial error (remote end didnt answer) then we should not retry.
func ReuseErrShouldRetry(err error) bool {
	if err == nil {
		return false // hey, it worked! no need to retry.
	}

	// if it's a network timeout error, it's a legitimate failure.
	if nerr, ok := err.(net.Error); ok && nerr.Timeout() {
		return false
	}

	errno, ok := err.(syscall.Errno)
	if !ok { // not an errno? who knows what this is. retry.
		return true
	}

	switch errno {
	case syscall.EADDRINUSE, syscall.EADDRNOTAVAIL:
		return true // failure to bind. retry.
	case syscall.ECONNREFUSED:
		return false // real dial error
	default:
		return true // optimistically default to retry.
	}
}