Added leave-channel command.

commands/leave-channel.js

+const errors = require('../errors.json');
+const config = require('../config.json');
+
+exports.run = async (client, message , args, connection) => {
+    if(!message.member.hasPermission('ADMINISTRATOR')) {
+            message.channel.send(errors.insufficient_permission_for_user).catch(e => {
+            return;
+        });
+    };
+    if (!args[0]) {
+        message.channel.send(`${errors.insufficient_args}`).catch(e => {
+            return;
+        });
+        return;
+    };
+    let channel;
+    await connection.query(`SELECT channel FROM leave_channel WHERE guild ='${message.guild.id}'`, function (err, result) {
+        if (err) {
+            throw err;
+        };
+        if (result.length > 0) {
+            channel = result[0].channel;
+        } else {
+            channel = "none";
+        };
+    });
+    if (args[0] == "reset") {
+        if (channel == "none"){
+            message.channel.send(errors.not_existing_on_db).catch(e => {
+                return;
+            });
+            return;
+        } else {
+            await connection.query(`DELETE FROM leave_channel WHERE guild ='${message.guild.id}'`, function (err, result) {
+                if (err){
+                    throw err;
+                };
+            });
+            message.channel.send('Successful!').catch(e => {
+                return;
+            });
+        };
+    } else if (!message.mentions.channels.first()) {
+        message.channel.send(errors.insufficient_args).catch(e => {
+            return;
+        });
+    } else if (message.mentions.channels.first()) {
+        if (channel == "none") {
+            connection.query(`INSERT INTO leave_channel (guild, channel) VALUES ('${message.guild.id}', '${message.mentions.channels.first().id}')`, function (err, result) {
+                if (err) {
+                    throw err;
+                };
+            });
+        } else {
+            const prefixdb = await new Promise((resolve, reject) => {
+                connection.query(`SELECT prefix FROM prefixes WHERE guild ='${message.guild.id}'`, function (err, result) {
+                    if (err)
+                        reject(err);
+                    resolve(result);
+                });
+            });
+            var prefix;
+            if(prefixdb.length < 1) {
+                prefix = config.prefix;
+                } else {
+                prefix = prefixdb[0].prefix;
+            };
+            message.channel.send(`Leave channel is already existing. To reset type \`${prefix}leave-channel reset\`.`).catch(e => {
+                return;
+            });
+        };
+    };
+};
+
+module.exports.help = {
+    name: 'leave-channel',
+    aliases: ['leave_channel', 'leavechannel']
+};