const outfields = require('graphql-outfields');

// Let's say the client issues a GraphQL query like this
query {
	user(id:5){
		username
		profile_pic { small }
	}
	location(city: 'South Park') {
		state
		zipcode
	}
}

// In your resolver
let resolver = (root, args, ctx, info) => {
	let { fields, has } = outfields.parser(info);
	/**
	* fields now looks like this:
	*{
	*	user: {
	*		username: true,
	*		profile_pic: {
	*			small: true
	*		}
	*	},
	*	location: {
	*		state: true,
	*		zipcode: true
	*	}
	*}
	*/
	assert.ok(fields.user.username);
	// However the parser may still require you to check properties along the way,
	// so nested objects can get ugly, instead of this
	if (fields.user && fields.user.profile_pic && fields.user.profile_pic.small) {
		// ...do stuff
	}
	// You can do this
	if (has('user.profile_pic.small')) {
		// ...do stuff
	}
	
	// If you just want to check a single field and nothing else
	// `graphql-outfields` has a top level has method 
	if (outfields.has(info, 'location.state')) {
		// They asked for the state in the location query
	}
	
	if (outfields.has(info, 'user.profile_pic.small')) {
		// They asked for the small profile picture
	}
};