server.js

const express = require("express");
const mysql = require("mysql2/promise");
require("dotenv").config();
const path = require("path");   

const app = express();
app.use(express.json());

const cors = require("cors");
app.use(cors());

app.use(express.static(path.join(__dirname)));

const DB_HOST = process.env.DB_HOST || "127.0.0.1";
const DB_PORT = process.env.DB_PORT ? Number(process.env.DB_PORT) : 3306;
const DB_USER = process.env.DB_USER || "root";
const DB_PASS = process.env.DB_PASS || "";
const DB_NAME = process.env.DB_NAME || "counter_db";
const PORT = process.env.PORT ? Number(process.env.PORT) : 3000;

const pool = mysql.createPool({
  host: DB_HOST,
  port: DB_PORT,
  user: DB_USER,
  password: DB_PASS,
  database: DB_NAME,
  waitForConnections: true,
  connectionLimit: 10,
  queueLimit: 0,
});

app.get("/counter", async (req, res) => {
  try {
    const [rows] = await pool.query("SELECT value FROM counter WHERE id = 1");
    if (!rows || rows.length === 0) {
      return res.status(500).json({ error: "counter row missing in DB" });
    }
    return res.json({ value: rows[0].value });
  } catch (err) {
    console.error("GET /counter error:", err);
    return res.status(500).json({ error: err.message });
  }
});

app.post("/counter/increment", async (req, res) => {
  let conn;
  try {
    conn = await pool.getConnection();
    await conn.beginTransaction();

    await conn.query("UPDATE counter SET value = value + 1 WHERE id = 1");

    const [rows] = await conn.query("SELECT value FROM counter WHERE id = 1");
    if (!rows || rows.length === 0) {
      await conn.rollback();
      return res.status(500).json({ error: "counter row missing after update" });
    }
    const newValue = rows[0].value;

    await conn.commit();
    return res.json({ value: newValue });
  } catch (err) {
    if (conn) {
      try { await conn.rollback(); } catch (_) {}
    }
    console.error("POST /counter/increment error:", err);
    return res.status(500).json({ error: err.message });
  } finally {
    if (conn) conn.release();
  }
});

app.listen(PORT, () => {
  console.log(`Server listening on http://localhost:${PORT}`);
});