server.ts

import express from "express";
import { v4 as uuid } from "uuid";
import Database from "better-sqlite3";

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

const db = new Database("orders.db");

db.prepare(
  "CREATE TABLE IF NOT EXISTS orders (id TEXT, side TEXT, price REAL, quantity REAL, status TEXT)"
).run();

app.post("/orders",(req,res)=>{
  const side=req.body.side;
  const price=req.body.price;
  const quantity=req.body.quantity;

  if(!side||!price||!quantity){
    res.status(400).json({error:"invalid input"});
    return;
  }

  const id=uuid();
  const status="OPEN";

  db.prepare(
    "INSERT INTO orders VALUES (?,?,?,?,?)"
  ).run(id,side,price,quantity,status);

  let match;

  if(side==="BUY"){
    match=db.prepare(
      "SELECT * FROM orders WHERE side='SELL' AND status='OPEN' AND price<=? ORDER BY price ASC LIMIT 1"
    ).get(price);
  }else{
    match=db.prepare(
      "SELECT * FROM orders WHERE side='BUY' AND status='OPEN' AND price>=? ORDER BY price DESC LIMIT 1"
    ).get(price);
  }

  if(match){
    db.prepare("UPDATE orders SET status='FILLED' WHERE id=?").run(id);
    db.prepare("UPDATE orders SET status='FILLED' WHERE id=?").run(match.id);
  }

  res.json({orderId:id,status:match?"FILLED":"OPEN"});
});

app.listen(3000,()=>{
  console.log("server running on 3000");
});