const graphql = require('graphql');

const { GraphQLObjectType, GraphQLString,
       GraphQLID, GraphQLInt, GraphQLSchema } = graphql;

//Schema defines data on the Graph like object types(book type), relation between
//these object types and descibes how it can reach into the graph to interact with
//the data to retrieve or mutate the data

var books = [
    { name:"Book 1", pages:432 , id:1},
    { name: "Book 2", pages: 32, id: 2},
    { name: "Book 3", pages: 532, id: 3 }
]

const BookType = new GraphQLObjectType({
    name: 'Book',
    fields: () => ({
        id: { type: GraphQLID  },
        name: { type: GraphQLString },
        pages: { type: GraphQLInt }
    })
});

//RootQuery describe how users can use the graph and grab data.
//E.g Root query to get all authors, get all books, get a particular book
//or get a particular author.
const RootQuery = new GraphQLObjectType({
    name: 'RootQueryType',
    fields: {
        book: {
            type: BookType,
            //argument passed by the user while making the query
            args: { id: { type: GraphQLID } },
            resolve(parent, args) {
                //Here we define how to get data from database source

                //this will return the book with id passed in argument by the user
                return books.find((item) => { return item.id == args.id});
            }
        }
    }
});

//Creating a new GraphQL Schema, with options query which defines query
//we will allow users to use when they are making request.
module.exports = new GraphQLSchema({
    query: RootQuery
});