Add deduper feature to the bot

features/deduper.js

@@ -0,0 +1,61 @@
+const deduper = {
+  monitoredChannels: [
+    "102860784329052160", // #general
+    "103696749012467712", // #need-help-0
+    "565213527673929729" // #need-help-1
+  ],
+
+  dupeExpireTime: 2 * 60 * 1000, // 2 minutes to reject the duplicate as cross-post (ms)
+  cleanerInterval: 10 * 60 * 1000, // Frees up the memory from 10 to 10 minutes (ms)
+
+  lastMessageOfMember: {},
+
+  deleteMsgAndWarnUser: (msg, lastMsg) => {
+    msg.delete();
+    // prettier-ignore
+    msg.author
+        .send(`Hello there! It looks like you just posted a message to the #${msg.channel.name} channel on our server.
+
+We don't allow cross-posting, so I had to delete your message because it is identical as your last one posted on #${lastMsg.channel.name}. You can avoid this warning deleting the first message or waiting 2 minutes.
+
+Thank you :)
+
+:robot: This message was sent by a bot, please do not respond to it - in case of additional questions / issues, please contact one of our mods!`);
+  },
+
+  handleMessage: ({ msg, user }) => {
+    if (deduper.monitoredChannels.includes(msg.channel.id)) {
+      const userId = user.id;
+      const lastMessage = deduper.lastMessageOfMember[userId];
+
+      if (
+        lastMessage &&
+        !lastMessage.deleted &&
+        lastMessage.channel.id !== msg.channel.id &&
+        lastMessage.content === msg.content &&
+        msg.createdTimestamp - lastMessage.createdTimestamp <
+          deduper.dupeExpireTime
+      ) {
+        deduper.deleteMsgAndWarnUser(msg, lastMessage);
+      } else {
+        deduper.lastMessageOfMember[userId] = msg;
+      }
+    }
+  },
+
+  registerCleaner: () => {
+    setInterval(() => {
+      Object.keys(deduper.lastMessageOfMember).forEach(userId => {
+        const msg = deduper.lastMessageOfMember[userId];
+
+        if (Date.now() - msg.createdTimestamp > deduper.dupeExpireTime) {
+          delete deduper.lastMessageOfMember[userId];
+        }
+      });
+    }, deduper.cleanerInterval);
+  }
+};
+
+module.exports = {
+  default: deduper
+};

index.js

@@ -12,6 +12,7 @@ const autoban = require("./features/autoban").default;
 const commands = require("./features/commands").default;
 const witInvite = require("./features/wit-invite").default;
 const stats = require("./features/stats").default;
+const deduper = require("./features/deduper").default;
 
 const bot = new discord.Client();
 bot.login(process.env.DISCORD_HASH);
@@ -81,6 +82,9 @@ logger.add(channelLog(bot, "479862475047567361"));
 // Amplitude metrics
 stats(bot);
 
+// start deduper cleaner
+deduper.registerCleaner();
+
 // reactiflux
 channelHandlers.addHandler("103882387330457600", jobs);
 channelHandlers.addHandler("541673256596537366", witInvite); // #women-in-tech
@@ -94,6 +98,7 @@ channelHandlers.addHandler("479862475047567361", qna); // #general
 channelHandlers.addHandler("*", commands);
 // channelHandlers.addHandler('*', codeblock);
 channelHandlers.addHandler("*", autoban);
+channelHandlers.addHandler("*", deduper);
 
 bot.on("messageReactionAdd", (reaction, user) => {
   channelHandlers.handleReaction(reaction, user);