index.js

const express = require('express')
const app = express()

app.use(express.json())

var date_time = new Date();

let notes = [
  {
    id: "1",
    name: "ABC",
    number: "1234"
  },
  {
    id: "2",
    name: "DEF",
    number: "5678"
  },
  {
    id: "3",
    name: "GHI",
    number: "9101"
  },
  {
    id: "4",
    name: "JKL",
    number: "1121"
  }
]

app.get('/info', (request, response) => {
    response.send(`Phonebook has info for ${notes.length} people, time is ${date_time}`)
})

const generateId = () => {
    const maxId = notes.length > 0
      ? Math.max(...notes.map(n => Number(n.id)))
      : 0
    return String(maxId + 1)
  }
  
  app.post('/api/persons', (request, response) => {
    const body = request.body
  
    if (!body.number) {
      return response.status(400).json({ 
        error: 'number missing' 
      })
    }
    if (!body.name) {
        return response.status(400).json({ 
          error: 'name missing' 
        })
    }
    var result = notes.filter(x => x.name === body.name);
    console.log(result)
    if (result.length > 0) {
        return response.status(400).json({ 
            error: 'name must be unique'
          })
    }
  
    const note = {
      name: body.name,
      number: body.number,
      id: generateId(),
    }
  
    notes = notes.concat(note)
  
    response.json(note)
  })

app.get('/api/persons/:id', (request, response) => {
    const id = request.params.id
    const note = notes.find(note => note.id === id)

    if (note) {
        response.json(note)
    } else {
        response.status(404).end()
    }
})

app.delete('/api/persons/:id', (request, response) => {
    const id = request.params.id
    notes = notes.filter(note => note.id !== id)

    response.status(204).end()
})

app.get('/', (request, response) => {
    response.send('<h1>Hello World!</h1>')
})
  
app.get('/api/persons', (request, response) => {
    response.json(notes)
})

const PORT = 3001
app.listen(PORT)
console.log(`Server running on port ${PORT}`)