feat: ユーザが退出した際、generalで通知する

src/discord.ts

@@ -28,6 +28,7 @@ import { PinPrefixEvent } from './events/pin-prefix'
 import { VCSpeechLogMessageUrlEvent } from './events/vc-speech-log-url'
 import { OriginCommand } from './commands/origin'
 import { JoinedNotifierEvent } from './events/joined-notifier'
+import { LeavedNotififerEvent } from './events/leaved-notifier'
 import { TweetEmbedEvent } from './events/tweet-embed'
 
 export class Discord {
@@ -76,6 +77,7 @@ export class Discord {
       new PinPrefixEvent(this),
       new VCSpeechLogMessageUrlEvent(this),
       new JoinedNotifierEvent(this),
+      new LeavedNotififerEvent(this),
       new TweetEmbedEvent(this),
     ]
     for (const event of events) {

src/events/leaved-notifier.ts

@@ -0,0 +1,32 @@
+import { ChannelType, GuildMember } from 'discord.js'
+import { BaseDiscordEvent } from '.'
+import { Configuration } from '@/config'
+
+/**
+ * ユーザーがサーバから退出した際、以下の処理を行う
+ * - #general で退出したことを通知する
+ */
+export class LeavedNotififerEvent extends BaseDiscordEvent<'guildMemberRemove'> {
+  get eventName(): 'guildMemberRemove' {
+    return 'guildMemberRemove'
+  }
+
+  async execute(member: GuildMember): Promise<void> {
+    const config: Configuration = this.discord.getConfig()
+    const generalChannelId =
+      config.get('discord').channel?.general || '1138605147287728150'
+
+    const generalChannel =
+      await this.discord.client.channels.fetch(generalChannelId)
+    if (!generalChannel || generalChannel.type !== ChannelType.GuildText) {
+      throw new Error('generalChannel is not found')
+    }
+
+    // general チャンネルがあるサーバ以外は無視
+    if (generalChannel.guildId !== member.guild.id) return
+
+    // #general で参加したことを通知する
+    const generalMessageContent = `:wave:<@${member.id}>さんが jao Gamers Club から退出しました。`
+    await generalChannel.send(generalMessageContent)
+  }
+}