const typeDefs = /* GraphQL */ `
  type Author {
    id: ID! # the ! means that every author object _must_ have an id
    firstName: String
    lastName: String
    """
    the list of Posts by this author
    """
    posts: [Post]
  }

  type Post {
    id: ID!
    title: String
    author: Author
    votes: Int
  }

  # the schema allows the following query:
  type Query {
    posts: [Post]
  }

  # this schema allows the following mutation:
  type Mutation {
    upvotePost(postId: ID!): Post
  }

  # we need to tell the server which types represent the root query
  # and root mutation types. We call them RootQuery and RootMutation by convention.
  schema {
    query: Query
    mutation: Mutation
  }
`
export default typeDefs

const resolvers = {
  Query: {
    posts() {
      return posts
    }
  },
  Mutation: {
    upvotePost(_, { postId }) {
      const post = find(posts, { id: postId })
      if (!post) {
        throw new Error(`Couldn't find post with id ${postId}`)
      }
      post.votes += 1
      return post
    }
  },
  Author: {
    posts(author) {
      return filter(posts, { authorId: author.id })
    }
  },
  Post: {
    author(post) {
      return find(authors, { id: post.authorId })
    }
  }
}
export default resolvers

import { makeExecutableSchema } from '@graphql-tools/schema'
const executableSchema = makeExecutableSchema({
  typeDefs,
  resolvers
})

const { createYoga } = require('graphql-yoga')
const { createServer } = require('http')
const yoga = createYoga({
  schema: executableSchema
})
const server = createServer(yoga)
server.listen(4000, () => {
  console.log('Yoga is listening at https://localhost:4000/graphql')
})