Defer responding to a message request

Previously if two message requests appered in a short timespan
in the same channel, the bot would reply twice (in two messages)
for the first message.

This commit fixes that, by queuing message requests and responding
to them in the chronological order based on a channelId.
(requests are queued to a queue identified by channelId)

fixes #4

src/index.ts

@@ -21,10 +21,23 @@ discord.on("ready", async event => {
   console.log(`Connected to Discord as ${event.user.tag} (${event.user.id})`);
 });
 
+const channelsRunning: DiscordApi.Collection<string, DiscordApi.Message[]> = new DiscordApi.Collection();
+
 discord.on("messageCreate", async message => {
   if (message.author.bot) return;
   if (!message.mentions.has(message.client.user)) return;
 
+  const messagesForChannel = channelsRunning.ensure(message.channelId, () => {return [] as DiscordApi.Message[];} );
+  const shouldStart = messagesForChannel.length == 0;
+  messagesForChannel.push(message);
+  if (shouldStart)
+    onMessage(message.channelId);
+});
+
+async function onMessage(channel: string) {
+  const channelQueue = channelsRunning.get(channel) as DiscordApi.Message[];
+  const message = channelQueue.at(0) as DiscordApi.Message;
+
   try {
     let messages: DiscordApi.Collection<string, DiscordApi.Message> = await message.channel.messages.fetch({ limit: config.limits.messages, cache: false });
 
@@ -73,6 +86,12 @@ discord.on("messageCreate", async message => {
       }
     });
   }
-});
+
+  channelQueue.shift();
+  if (channelQueue.length == 0)
+    channelsRunning.delete(channel);
+  else
+    onMessage(channel);
+}
 
 discord.login(config.tokens.Discord);