Add support for extended-monitor

See: https://github.com/ircv3/ircv3-specifications/pull/466

irc/monitor.go

@@ -6,6 +6,8 @@ package irc
 import (
 	"sync"
 
+	"github.com/ergochat/ergo/irc/caps"
+
 	"github.com/ergochat/irc-go/ircmsg"
 )
 
@@ -23,6 +25,17 @@ func (mm *MonitorManager) Initialize() {
 	mm.watchedby = make(map[string]map[*Session]empty)
 }
 
+// AddMonitors adds clients using extended-monitor monitoring `client`'s nick to the passed user set.
+func (manager *MonitorManager) AddMonitors(users map[*Session]empty, cfnick string, capabs ...caps.Capability) {
+	manager.RLock()
+	defer manager.RUnlock()
+	for session := range manager.watchedby[cfnick] {
+		if session.capabilities.Has(caps.ExtendedMonitor) && session.capabilities.HasAll(capabs...) {
+			users[session] = empty{}
+		}
+	}
+}
+
 // AlertAbout alerts everyone monitoring `client`'s nick that `client` is now {on,off}line.
 func (manager *MonitorManager) AlertAbout(nick, cfnick string, online bool) {
 	var watchers []*Session