API Design & Gateway

# REST এ এটার জন্য 3টা API call লাগতো
# GraphQL এ একটাই
query GetUserDashboard {
  user(id: "123") {
    name
    avatar
    posts(first: 5) {
      title
      createdAt
    }
    followers {
      count
    }
  }
}

# Mutation — data change করতে
mutation UpdateProfile($name: String!, $bio: String) {
  updateUser(input: { name: $name, bio: $bio }) {
    id
    name
    updatedAt
  }
}

// Service definition
syntax = "proto3";

service UserService {
  rpc GetUser (UserRequest) returns (UserResponse);
  rpc ListUsers (ListRequest) returns (stream UserResponse);
}

message UserRequest {
  string user_id = 1;
}

message UserResponse {
  string id = 1;
  string name = 2;
  string email = 3;
  int32  age = 4;
}
// protoc দিয়ে Python/Go/Java/Node code generate হবে

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

// GET /api/v1/users/:id
app.get('/api/v1/users/:id', async (req, res) => {
  try {
    const user = await User.findById(req.params.id);
    if (!user) return res.status(404).json({
      error: 'User not found', code: 'USER_NOT_FOUND'
    });
    res.status(200).json({ data: user });
  } catch (err) {
    res.status(500).json({ error: 'Internal server error' });
  }
});

// POST /api/v1/users — create user
app.post('/api/v1/users', async (req, res) => {
  const { name, email, password } = req.body;
  if (!name || !email) return res.status(400).json({
    error: 'name and email required'
  });
  const user = await User.create({ name, email, password });
  res.status(201).json({ data: user });
});

// PATCH /api/v1/users/:id — partial update
app.patch('/api/v1/users/:id', async (req, res) => {
  const updated = await User.findByIdAndUpdate(
    req.params.id, req.body, { new: true }
  );
  res.json({ data: updated });
});

const rateLimit = require('express-rate-limit');
const RedisStore = require('rate-limit-redis');

// API Rate limit: 100 requests per 15 minutes per IP
const apiLimiter = rateLimit({
  windowMs: 15 * 60 * 1000,  // 15 minutes
  max: 100,
  standardHeaders: true,
  store: new RedisStore({ client: redisClient }),
  handler: (req, res) => {
    res.status(429).json({
      error: 'Too many requests',
      retryAfter: Math.ceil(res.getHeader('Retry-After'))
    });
  }
});

app.use('/api/', apiLimiter);