Improve whitelist feature

* Use a primary autoincrementing primary key because primary keys need
  to be unique
* Cache whitelist on bot startup / only read from database once
* "Externalize" whitelist checking to the messageCreate function.

commands/admin/whitelist.js

@@ -2,15 +2,22 @@ const sqlite3 = require('sqlite3').verbose();
 
 module.exports = {
     name: 'whitelist',
-    description: 'Whitelist different commands that need whitelisting.',
+    description: 'Whitelist a command in a specific server.',
     admin: true,
-    async execute({message, args, prefix}) {
+    async execute({message, args, prefix, client}) {
         if(args < 2){
             message.channel.send(`You need to supply the command and channel that you want to whitelist\n\`${prefix}whitelist <command> <server_id>\``);
             return;
         } 
         let command = args[0];
         let guild = args[1];
+        if(guild === "this") guild = message.guild.id;
+        // TODO: Add ability to remove server from whitelist.
+        const whitelistedCommands = client.whitelist.get("guild");
+        if(whitelistedCommands && whitelistedCommands.includes(command)){
+            message.channel.send("Command is already whitelisted in that server.")
+            return;
+        }
         // TODO: First check if the bot has access to that guild before whitelisting.
         const databasePath = 'data/database.db'
         const db = new sqlite3.Database(databasePath)
@@ -35,8 +42,15 @@ module.exports = {
                 }
             });
         })
-        if(!err)
+        if(!err){
+            if(whitelistedCommands){
+                whitelistedCommands.push(command);
+			    client.whitelist.set(guild, whitelistedCommands);
+            }else {
+                client.whitelist.set(guild, command);
+            }
             message.channel.send("Command has been whitelisted in this server.")
-        else message.channel.send("Could not whitelist the server with that command. Check the logs.")
+
+        } else message.channel.send("Could not whitelist the server with that command. Check the logs.")
     }
 };