Added status change notification.

Currently this feature doesn't properly work because of the discord.js library, it seems there's a bug that makes oldMember and newMember inside the presenceUpdate event handler have the same presence. discordjs/discord.js#3214

src/app.js

@@ -102,7 +102,46 @@ client.on('message', async message => {
 });
 
 client.on('presenceUpdate', (oldMember, newMember) => {
-  // Handle notifications.
+  logger.debug(oldMember.displayName, oldMember.presence.status, newMember.presence.status)
+
+  // Check if we're interested in this member's presenceUpdate.
+  if (oldMember.presence.status == newMember.presence.status) return;
+
+  // Check if the member updating does correspond to one stored in the realm.
+  const realmEntry = realm.objects('Guilds').filtered(`id = "${oldMember.guild.id}"`);
+
+  // Check if realmEntry is empty, which means it does not correspond to a stored guild.
+  if (realmEntry.length == 0) return;
+
+  // Check if member is stored in the realmEntry.
+  const id = realmEntry[0].listening.find( entry => entry == oldMember.id);
+  if (!id) return;
+
+  // Check if status changed.
+  let messageToSend = undefined;
+  if (oldMember.presence.status == 'online' && newMember.presence.status == 'offline') {
+    messageToSend = `The bot ${oldMember} has gone offline.`;
+  } else if (oldMember.presence.status != 'online' && newMember.presence.status == 'online') {
+    messageToSend = `The bot ${newMember} is now online.`;
+  }
+
+  // Here, we can assume that the realm entry will have a channel id stored.
+  const channelID = realmEntry[0].channel;
+
+  // Send the notification and handle permissions and unknown channel errors.
+  client.channels.fetch(channelID)
+    .then( channel => channel.send(messageToSend))
+    .catch( err => {
+      if (err == 'DiscordAPIError: Unknown Channel') {
+        oldMember.guild.owner.send(`The bot **${oldMember.displayName}** in the server **${oldMember.guild.name}** has changed its status but I couldn't send a message to the channel you set-up previously. It has probably been deleted. Please, change the broadcasting channel in **${oldMember.guild.name}** with **${config.prefix}channel** and mention the channel you want to set-up.`);
+      } else if (err == 'DiscordAPIError: Missing Permissions') {
+        oldMember.guild.owner.send(`The bot **${oldMember.displayName}** in the server **${oldMember.guild.name}** has changed its status but I couldn't send a message to the channel you set-up previously because I don't have permissions to send messages there. Please, allow me to send messages in the set channel or change the broadcasting channel in **${oldMember.guild.name}** with **${config.prefix}channel** and mention the channel you want to set-up.`);
+      } else {
+        oldMember.guild.owner.send(`The bot **${oldMember.displayName}** in the server **${oldMember.guild.name}** has changed its status but I couldn't send a message to the channel you set-up because something unexpected went wrong.`);
+        logger.error(`Something went wrong when handling ${oldMember.guild.name}'s ${oldMember.displayName} presence update.`);
+        logger.error(err);
+      }
+    });
 });
 
 client.on('guildCreate', guild => {

src/commands/add.js

@@ -15,8 +15,6 @@ module.exports = {
     }
 
     // Check if there's a channel entry in realm.
-    // Technically this check is not necessary, because we've designed this so that the initial guild entry
-    // is added when a valid text channel is specified in the argument of the channel command.
     if (!realmEntry[0].channel) {
       message.reply(`before adding any bots, you need to define in which channel I should send the notifications. Please define the broadcasting text channel with **${options.config.prefix}channel** and mention the text channel you want to set.`);
       return;

src/commands/channel.js

@@ -14,8 +14,6 @@ module.exports = {
         message.reply(`a broadcasting text channel is yet to be defined. You can define one by running **${options.config.prefix}channel** and mentioning the text channel you want to set.`);
       } else {
         // Check if there's a channel realm entry.
-        // Technically this check is not necessary, because we've designed this so that the initial guild entry
-        // is added when a valid text channel is specified in the argument.
         if (!realmEntry[0].channel) {
           message.reply(`a broadcasting text channel is yet to be defined. You can define one by running **${options.config.prefix}channel** and mentioning the text channel you want to set.`);
           return;