package statsd

import (
	"errors"
	"fmt"
	"net"
	"os"
	"time"
)

const (
	autoHostEnvName = "DD_AGENT_HOST"
	autoPortEnvName = "DD_DOGSTATSD_PORT"
	defaultUDPPort  = "8125"
)

// udpWriter is an internal class wrapping around management of UDP connection
type udpWriter struct {
	conn net.Conn
}

// New returns a pointer to a new udpWriter given an addr in the format "hostname:port".
func newUDPWriter(addr string) (*udpWriter, error) {
	if addr == "" {
		addr = addressFromEnvironment()
	}
	if addr == "" {
		return nil, errors.New("No address passed and autodetection from environment failed")
	}

	udpAddr, err := net.ResolveUDPAddr("udp", addr)
	if err != nil {
		return nil, err
	}
	conn, err := net.DialUDP("udp", nil, udpAddr)
	if err != nil {
		return nil, err
	}
	writer := &udpWriter{conn: conn}
	return writer, nil
}

// SetWriteTimeout is not needed for UDP, returns error
func (w *udpWriter) SetWriteTimeout(d time.Duration) error {
	return errors.New("SetWriteTimeout: not supported for UDP connections")
}

// Write data to the UDP connection with no error handling
func (w *udpWriter) Write(data []byte) (int, error) {
	return w.conn.Write(data)
}

func (w *udpWriter) Close() error {
	return w.conn.Close()
}

func (w *udpWriter) remoteAddr() net.Addr {
	return w.conn.RemoteAddr()
}

func addressFromEnvironment() string {
	autoHost := os.Getenv(autoHostEnvName)
	if autoHost == "" {
		return ""
	}

	autoPort := os.Getenv(autoPortEnvName)
	if autoPort == "" {
		autoPort = defaultUDPPort
	}

	return fmt.Sprintf("%s:%s", autoHost, autoPort)
}