feat: basic database setup

backend/src/db.js

@@ -0,0 +1,70 @@
+// copied from one of my older projects
+const mysql = require('mysql2/promise');
+
+function getEnvVar(name) {
+  const value = process.env[name];
+  if (value === null) {
+    throw new Error(`Environment variable ${name} is not defined`);
+  }
+  return value;
+}
+
+const pool = mysql.createPool({
+  host: getEnvVar('MYSQL_HOST'),
+  user: getEnvVar('MYSQL_USER'),
+  password: getEnvVar('MYSQL_PASSWORD'),
+  database: getEnvVar('MYSQL_DB'),
+});
+
+const migrations = [
+  {
+    name: "init_dart_table",
+    up: async (conn) => {
+      await conn.query(`
+        CREATE TABLE dart (
+          id INT PRIMARY KEY AUTO_INCREMENT
+        )
+      `);
+    }
+  }
+];
+
+async function initDB() {
+  await pool.query(`
+    CREATE TABLE IF NOT EXISTS migrations (
+      id INT PRIMARY KEY AUTO_INCREMENT,
+      name VARCHAR(255) NOT NULL UNIQUE
+    );
+  `);
+
+  for (const m of migrations) {
+    const conn = await pool.getConnection();
+
+    try {
+      await conn.beginTransaction();
+
+      const [rows] = await conn.query(
+        `SELECT 1 FROM migrations WHERE name = ? LIMIT 1 FOR UPDATE`,
+        [m.name]
+      );
+
+      if (rows.length === 0) {
+        console.log(`Running migration: ${m.name}`);
+        await m.up(conn);
+        await conn.query(`INSERT INTO migrations (name) VALUES (?)`, [m.name]);
+      }
+
+      await conn.commit();
+    } catch (err) {
+      await conn.rollback();
+      throw err;
+    } finally {
+      conn.release();
+    }
+  }
+}
+
+module.exports = {
+  pool,
+  initDB
+};