Add currency commands and polish utilities

commands/db/balance.js

@@ -0,0 +1,26 @@
+const { SlashCommandBuilder } = require('discord.js');
+const { connectToDatabase } = require('../../db.js');
+
+module.exports = {
+    data: new SlashCommandBuilder()
+        .setName('balance')
+        .setDescription('Check your coin balance or another user\'s balance.')
+        .addUserOption(option =>
+            option
+                .setName('user')
+                .setDescription('User to check (defaults to you)')
+                .setRequired(false)),
+    async execute(interaction) {
+        const dbClient = await connectToDatabase();
+        const db = dbClient.db('discord');
+        const collection = db.collection('currency');
+
+        const target = interaction.options.getUser('user') ?? interaction.user;
+        const targetData = await collection.findOne({ userID: target.id });
+        const balance = targetData?.balance ?? 0;
+
+        return interaction.reply({
+            content: `${target.tag} has **${balance}** coins.`,
+        });
+    }
+};