package server

import (
	"flag"
	"fmt"
	"os"

	"github.com/asaskevich/govalidator"
)

// GetListenAddressFromEnvOrFlags will check flag --host and --port to construct the listen address
// If they doesn't exist it will fallback on HOST and PORT environment variable and finally fallback
// to the default value localhost:8080.
func GetListenAddressFromEnvOrFlags() (string, error) {
	host := os.Getenv("HOST")
	port := os.Getenv("PORT")

	if host == "" {
		host = "localhost"
	}
	if port == "" {
		port = "8080"
	}

	pHost := flag.String("host", host, "Host address to listen to")
	pPort := flag.String("port", port, "Port to listen to")

	if !govalidator.IsHost(*pHost) {
		return "", fmt.Errorf("provided 'host' is invalid")
	}

	if !govalidator.IsPort(*pPort) {
		return "", fmt.Errorf("provided 'port' is invalid")
	}

	return fmt.Sprintf("%s:%s", *pHost, *pPort), nil
}