stacker.news/pages/index.js

import { useQuery, gql, useMutation } from '@apollo/client'
import { useState } from 'react'
import { useSession } from 'next-auth/client'
import styles from '../styles/index.module.css'
import Layout from '../components/layout'

function Users () {
  const { loading, error, data } = useQuery(gql`{ users { id, name } }`)
  if (error) return <div>Failed to load</div>
  if (loading) return <div>Loading...</div>
  const { users } = data
  return (
    <div>
      {users.map(user => (
        <div key={user.id}>{user.name}</div>
      ))}
    </div>
  )
}

function NewItem ({ parentId }) {
  const [session] = useSession()
  const [createItem] = useMutation(
    gql`
      mutation CreateItem($text: String!, $parentId: ID) {
        createItem(text: $text, parentId: $parentId) {
          id
        }
      }`, {
      update (cache, { data: { createItem } }) {
        cache.modify({
          fields: {
            items (existingItems = [], { readField }) {
              const newItemRef = cache.writeFragment({
                data: createItem,
                fragment: gql`
                    fragment NewItem on Item {
                      id
                      user {
                        name
                      }
                      text
                      depth
                    }
                  `
              })
              for (let i = 0; i < existingItems.length; i++) {
                if (readField('id', existingItems[i]) === parentId) {
                  return [...existingItems.slice(0, i), newItemRef, ...existingItems.slice(i)]
                }
              }
              return [newItemRef, ...existingItems]
            }
          }
        })
      }
    })
  const [open, setOpen] = useState(false)

  if (!session) return null

  if (!open) {
    return (
      <div onClick={() => setOpen(true)}>
        {parentId ? 'reply' : 'submit'}
      </div>
    )
  }

  let text
  return (
    <form
      style={{ marginLeft: '5px' }}
      onSubmit={e => {
        e.preventDefault()
        createItem({ variables: { text: text.value, parentId } })
        setOpen(false)
        text.value = ''
      }}
    >
      <textarea
        ref={node => {
          text = node
        }}
      />
      <button type='submit'>Submit</button>
    </form>
  )
}

function Items () {
  const { loading, error, data } = useQuery(
    gql`
      { items {
        id
        user {
          name
        }
        text
        depth
      } }`
  )
  if (error) return <div>Failed to load</div>
  if (loading) return <div>Loading...</div>
  const { items } = data
  return (
    <>
      <NewItem />
      <div>
        {items.map(item => (
          <div key={item.id} style={{ marginLeft: `${5 * item.depth}px` }}>
            <div>{item.user.name} : {item.text}</div>
            <NewItem parentId={item.id} />
          </div>
        ))}
      </div>
    </>
  )
}

export default function Index () {
  return (
    <Layout>
      <div className={`${styles.box} flashit`} />
      <Users />
      <Items />
    </Layout>
  )
}