app.js

const express = require('express')
const {MongoClient} = require('mongodb')
const fetch = require('node-fetch')

const app = express()
const PORT = 3000
const mongoUri = 'mongodb://127.0.0.1:27017'
const dbName = 'jsonPlaceholderDB'

app.use(express.json())

let db
let usersCollection, postsCollection, commentsCollection

async function connectDB() {
  const client = new MongoClient(mongoUri)
  await client.connect()
  db = client.db(dbName)
  usersCollection = db.collection('users')
  postsCollection = db.collection('posts')
  commentsCollection = db.collection('comments')
}

async function loadJSONPlaceholderData() {
  const [users, posts, comments] = await Promise.all([
    fetch('https://jsonplaceholder.typicode.com/users').then(res => res.json()),
    fetch('https://jsonplaceholder.typicode.com/posts').then(res => res.json()),
    fetch('https://jsonplaceholder.typicode.com/comments').then(res =>
      res.json(),
    ),
  ])

  await usersCollection.deleteMany({})
  await postsCollection.deleteMany({})
  await commentsCollection.deleteMany({})

  await usersCollection.insertMany(users.slice(0, 10))
  await postsCollection.insertMany(posts)
  await commentsCollection.insertMany(comments)
}

// GET /load
app.get('/load', async (req, res) => {
  try {
    await loadJSONPlaceholderData()
    res.sendStatus(200)
  } catch (err) {
    res.status(500).send('Failed to load data')
  }
})

// DELETE /users
app.delete('/users', async (req, res) => {
  await usersCollection.deleteMany({})
  res.send('All users deleted')
})

// DELETE /users/:userId
app.delete('/users/:userId', async (req, res) => {
  const userId = parseInt(req.params.userId)
  await usersCollection.deleteOne({id: userId})
  res.send(`User ${userId} deleted`)
})

// GET /users/:userId
app.get('/users/:userId', async (req, res) => {
  const userId = parseInt(req.params.userId)
  const user = await usersCollection.findOne({id: userId})

  if (!user) return res.status(404).send('User not found')

  const userPosts = await postsCollection.find({userId}).toArray()
  const allComments = await commentsCollection.find().toArray()

  const postsWithComments = userPosts.map(post => ({
    ...post,
    comments: allComments.filter(c => c.postId === post.id),
  }))

  res.json({user, posts: postsWithComments})
})

// PUT /users
app.put('/users', async (req, res) => {
  const newUser = req.body

  if (!newUser || !newUser.id) {
    return res.status(400).send('Invalid user data')
  }

  const existing = await usersCollection.findOne({id: newUser.id})

  if (existing) {
    return res.status(400).send('User already exists')
  }

  await usersCollection.insertOne(newUser)
  res.status(201).send('User added')
})

// Connect to DB and start server
connectDB()
  .then(() => {
    app.listen(PORT, () => {
      console.log(`Server running at http://localhost:${PORT}`)
    })
  })
  .catch(err => {
    console.error('Failed to connect to DB:', err)
  })