add GetReplyTarget (#105)

* add GetReplyTarget

See #97

* clarify error behavior

ircevent/irc_struct.go

@@ -9,6 +9,7 @@ import (
 	"crypto/tls"
 	"log"
 	"net"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -195,6 +196,42 @@ func (irc *Connection) labelNegotiated() bool {
 	return atomic.LoadUint32(&irc.capFlags)&capFlagLabeledResponse != 0
 }
 
+// GetReplyTarget attempts to determine where replies to a PRIVMSG or NOTICE
+// should be sent (a channel if the message was sent to a channel, a nick
+// if the message was a direct message from a valid nickname). If no valid
+// reply target can be determined, it returns the empty string.
+func (irc *Connection) GetReplyTarget(msg ircmsg.Message) string {
+	switch msg.Command {
+	case "PRIVMSG", "NOTICE", "TAGMSG":
+		if len(msg.Params) == 0 {
+			return ""
+		}
+		target := msg.Params[0]
+		chanTypes := irc.ISupport()["CHANTYPES"]
+		if chanTypes == "" {
+			chanTypes = "#"
+		}
+		for i := 0; i < len(chanTypes); i++ {
+			if strings.HasPrefix(target, chanTypes[i:i+1]) {
+				return target
+			}
+		}
+		// this was not a channel message: attempt to reply to the source
+		if nuh, err := msg.NUH(); err == nil {
+			if strings.IndexByte(nuh.Name, '.') == -1 {
+				return nuh.Name
+			} else {
+				// this is probably a server name
+				return ""
+			}
+		} else {
+			return ""
+		}
+	default:
+		return ""
+	}
+}
+
 // Deprecated; use (*ircmsg.Message).Nick() instead
 func ExtractNick(source string) string {
 	nuh, err := ircmsg.ParseNUH(source)

ircevent/irc_test.go

@@ -343,3 +343,35 @@ func TestConnectionCallbacks(t *testing.T) {
 	<-loopExited
 	assertEqual(disconnectCalled, true)
 }
+
+func mustParse(line string) ircmsg.Message {
+	msg, err := ircmsg.ParseLine(line)
+	if err != nil {
+		panic(err)
+	}
+	return msg
+}
+
+func TestGetReplyTarget(t *testing.T) {
+	irc := Connection{}
+	assertEqual(irc.GetReplyTarget(mustParse(":[email protected] PRIVMSG #ergo :hi")), "#ergo")
+	assertEqual(irc.GetReplyTarget(mustParse(":[email protected] PRIVMSG titlebot :hi")), "shivaram")
+	irc.isupport = map[string]string{
+		"CHANTYPES": "#&",
+	}
+	assertEqual(irc.GetReplyTarget(mustParse(":[email protected] PRIVMSG #ergo :hi")), "#ergo")
+	assertEqual(irc.GetReplyTarget(mustParse(":[email protected] PRIVMSG &ergo :hi")), "&ergo")
+	assertEqual(irc.GetReplyTarget(mustParse(":[email protected] PRIVMSG titlebot :hi")), "shivaram")
+	assertEqual(irc.GetReplyTarget(mustParse(":irc.ergo.chat NOTICE titlebot :Server is shutting down")), "")
+
+	// no source but it's a channel message
+	assertEqual(irc.GetReplyTarget(mustParse("PRIVMSG #ergo :hi")), "#ergo")
+	// no source but it's a DM (no way to reply)
+	assertEqual(irc.GetReplyTarget(mustParse("PRIVMSG titlebot :hi")), "")
+	// invalid messages
+	assertEqual(irc.GetReplyTarget(mustParse(":[email protected] PRIVMSG")), "")
+	assertEqual(irc.GetReplyTarget(mustParse("PRIVMSG")), "")
+	assertEqual(irc.GetReplyTarget(mustParse("PRIVMSG :")), "")
+	// not a PRIVMSG
+	assertEqual(irc.GetReplyTarget(mustParse(":testnet.ergo.chat 371 shivaram :This is Ergo version 2.13.0.")), "")
+}