From 8dc637e41ee4df834ae99bda17b6ab5f11be74f8 Mon Sep 17 00:00:00 2001
From: Knut Ahlers <knut@ahlers.me>
Date: Sat, 31 Jul 2021 00:54:28 +0200
Subject: [PATCH] Add clearchannel module

Signed-off-by: Knut Ahlers <knut@ahlers.me>
---
 mod_clearChannel.go | 94 +++++++++++++++++++++++++++++++++++++++++++++
 wiki/Home.md        | 10 +++++
 2 files changed, 104 insertions(+)
 create mode 100644 mod_clearChannel.go

diff --git a/mod_clearChannel.go b/mod_clearChannel.go
new file mode 100644
index 0000000..19ca4a6
--- /dev/null
+++ b/mod_clearChannel.go
@@ -0,0 +1,94 @@
+package main
+
+import (
+	"sort"
+	"strconv"
+	"time"
+
+	"github.com/bwmarrin/discordgo"
+	"github.com/pkg/errors"
+	"github.com/robfig/cron/v3"
+	log "github.com/sirupsen/logrus"
+)
+
+/*
+ * @module clearchannel
+ * @module_desc Cleans up old messages from a channel (for example announcement channel) which are older than the retention time
+ */
+
+func init() {
+	RegisterModule("clearchannel", func() module { return &modClearChannel{} })
+}
+
+type modClearChannel struct {
+	attrs   moduleAttributeStore
+	discord *discordgo.Session
+}
+
+func (m *modClearChannel) Initialize(crontab *cron.Cron, discord *discordgo.Session, attrs moduleAttributeStore) error {
+	m.attrs = attrs
+	m.discord = discord
+
+	if err := attrs.Expect(
+		"discord_channel_id",
+		"retention",
+	); err != nil {
+		return errors.Wrap(err, "validating attributes")
+	}
+
+	// @attr cron optional string "0 * * * *" When to execute the cleaner
+	if _, err := crontab.AddFunc(attrs.MustString("cron", ptrString("0 * * * *")), m.cronClearChannel); err != nil {
+		return errors.Wrap(err, "adding cron function")
+	}
+
+	return nil
+}
+
+func (m modClearChannel) cronClearChannel() {
+	var (
+		after = "0"
+
+		// @attr discord_channel_id required string "" ID of the Discord channel to clean up
+		channelID = m.attrs.MustString("discord_channel_id", nil)
+		// @attr retention required duration "" How long to keep messages in this channel
+		retention = m.attrs.MustDuration("retention", nil)
+	)
+
+	for {
+		msgs, err := m.discord.ChannelMessages(channelID, 100, "", after, "")
+		if err != nil {
+			log.WithError(err).Error("Unable to fetch announcement channel messages")
+			return
+		}
+
+		sort.Slice(msgs, func(i, j int) bool {
+			iu, _ := strconv.ParseUint(msgs[i].ID, 10, 64)
+			ju, _ := strconv.ParseUint(msgs[j].ID, 10, 64)
+			return iu < ju
+		})
+
+		if len(msgs) == 0 {
+			break
+		}
+
+		for _, msg := range msgs {
+			mt, err := msg.Timestamp.Parse()
+			if err != nil {
+				log.WithField("msg_id", msg.ID).WithError(err).Error("Unable to parse message timestamp")
+				break
+			}
+
+			if time.Since(mt) < retention {
+				// We got to the first message within the retention time, we can end now
+				break
+			}
+
+			if err = m.discord.ChannelMessageDelete(channelID, msg.ID); err != nil {
+				log.WithError(err).Error("Unable to delete messages")
+				return
+			}
+
+			after = msg.ID
+		}
+	}
+}
diff --git a/wiki/Home.md b/wiki/Home.md
index 0c3a9f7..da911a7 100644
--- a/wiki/Home.md
+++ b/wiki/Home.md
@@ -16,6 +16,16 @@ module_configs:
 
 # Modules
 
+## Type: `clearchannel`
+
+Cleans up old messages from a channel (for example announcement channel) which are older than the retention time
+
+| Attribute | Req. | Type | Default Value | Description |
+| --------- | :--: | ---- | ------------- | ----------- |
+| `discord_channel_id` | ✅ | string |  | ID of the Discord channel to clean up |
+| `retention` | ✅ | duration |  | How long to keep messages in this channel |
+| `cron` |  | string | `0 * * * *` | When to execute the cleaner |
+
 ## Type: `liveposting`
 
 Announces stream live status based on Discord streaming status