import fastify from 'fastify';

const app = fastify({ logger: true });

interface User {
    id: number;
    name: string;
    email: string;
    age: number;
}

app.post<{ Body: User; }> ('/api/users', async (request, reply) => {
    const user = request.body;

    const canDrink = user.age >= 21;
    const greeting = `Hello ${user.name.toUpperCase()}, your email ${user.email.toLowerCase()} has been recorded`;

    return { user, canDrink, greeting };
});

const start = async () => {
    try {
        await app.listen({ port: 3000 });
        console.log('Server running at http://localhost:3000');
    } catch (err) {
        app.log.error(err);
        process.exit(1);
    }
};

start();










/*
Try making a POST request with this "deranged" JSON:

{
  "id": "42",
  "name": 12345,
  "email": {"address": "bad@example.com"},
  "age": "twenty-one"
}

What happens:
1. TypeScript is happy at compile time (we said body is User)
2. Fastify accepts this JSON as valid (no runtime validation)
3. Code fails when trying operations like toUpperCase() on a number
   or comparing "twenty-one" >= 21
*/