From f70382876acbaa291296509b96f0d5579f4f7238 Mon Sep 17 00:00:00 2001
From: Knut Ahlers <knut@ahlers.me>
Date: Fri, 24 Dec 2021 20:23:38 +0100
Subject: [PATCH] [core] Add "follow" event using EventSub

Signed-off-by: Knut Ahlers <knut@ahlers.me>
---
 events.go          |  2 ++
 twitch/eventsub.go |  1 +
 twitchWatcher.go   | 27 +++++++++++++++++++++++++++
 wiki/Events.md     | 11 +++++++++++
 4 files changed, 41 insertions(+)

diff --git a/events.go b/events.go
index ddb1ee9..27203d4 100644
--- a/events.go
+++ b/events.go
@@ -6,6 +6,7 @@ var (
 	eventTypeBan             = ptrStr("ban")
 	eventTypeBits            = ptrStr("bits")
 	eventTypeClearChat       = ptrStr("clearchat")
+	eventTypeFollow          = ptrStr("follow")
 	eventTypeGiftPaidUpgrade = ptrStr("giftpaidupgrade")
 	eventTypeHost            = ptrStr("host")
 	eventTypeJoin            = ptrStr("join")
@@ -28,6 +29,7 @@ var (
 		eventTypeBan,
 		eventTypeBits,
 		eventTypeClearChat,
+		eventTypeFollow,
 		eventTypeGiftPaidUpgrade,
 		eventTypeHost,
 		eventTypeJoin,
diff --git a/twitch/eventsub.go b/twitch/eventsub.go
index a4b569f..50aa309 100644
--- a/twitch/eventsub.go
+++ b/twitch/eventsub.go
@@ -42,6 +42,7 @@ const (
 	// eventSubStatusUserRemoved          = "user_removed"
 	// eventSubStatusVerificationFailed   = "webhook_callback_verification_failed"
 
+	EventSubEventTypeChannelFollow = "channel.follow"
 	EventSubEventTypeChannelUpdate = "channel.update"
 	EventSubEventTypeStreamOffline = "stream.offline"
 	EventSubEventTypeStreamOnline  = "stream.online"
diff --git a/twitchWatcher.go b/twitchWatcher.go
index 124390a..ae7b16b 100644
--- a/twitchWatcher.go
+++ b/twitchWatcher.go
@@ -183,10 +183,37 @@ func (t *twitchWatcher) registerEventSubCallbacks(channel string) (func(), error
 		return nil, errors.Wrap(err, "registering channel-update eventsub")
 	}
 
+	unsubFollow, err := twitchEventSubClient.RegisterEventSubHooks(
+		twitch.EventSubEventTypeChannelFollow,
+		twitch.EventSubCondition{BroadcasterUserID: userID},
+		func(m json.RawMessage) error {
+			var payload twitch.EventSubEventFollow
+			if err := json.Unmarshal(m, &payload); err != nil {
+				return errors.Wrap(err, "unmarshalling event")
+			}
+
+			fields := plugins.FieldCollectionFromData(map[string]interface{}{
+				"channel":     channel,
+				"followed_at": payload.FollowedAt,
+				"user_id":     payload.UserID,
+				"user":        payload.UserLogin,
+			})
+
+			log.WithFields(log.Fields(fields.Data())).Info("User followed")
+			go handleMessage(ircHdl.Client(), nil, eventTypeFollow, fields)
+
+			return nil
+		},
+	)
+	if err != nil {
+		return nil, errors.Wrap(err, "registering channel-follow eventsub")
+	}
+
 	return func() {
 		unsubCU()
 		unsubSOff()
 		unsubSOn()
+		unsubFollow()
 	}, nil
 }
 
diff --git a/wiki/Events.md b/wiki/Events.md
index d9da712..be3ebc4 100644
--- a/wiki/Events.md
+++ b/wiki/Events.md
@@ -41,6 +41,17 @@ Fields:
 
 - `channel` - The channel the event occurred in
 
+## `follow`
+
+User followed the channel. This event is not de-duplicated and therefore might be used to spam! (Only available when EventSub support is available!)
+
+Fields:
+
+- `channel` - The channel the event occurred in
+- `followed_at` - Time object of the follow date
+- `user_id` - ID of the newly following user
+- `user` - The login-name of the user who followed
+
 ## `giftpaidupgrade`
 
 User upgraded their gifted subscription into a paid one. This event does not contain any details about the tier of the paid subscription.