feat: export a prepare function (#72)

Using `prepare` allows for building a `GraphQLOptions` object that is _not_ a callback.

src/gramps.js

@@ -100,7 +100,7 @@ const mapSourcesToExecutableSchemas = (sources, shouldMock, options) =>
  * @param  {Object?}   config.apollo          options for Apollo functions
  * @return {Function}                         req => options for `graphqlExpress()`
  */
-export default function gramps({
+export function prepare({
   dataSources = [],
   enableMockData = process.env.GRAMPS_MODE === 'mock',
   extraContext = req => ({}), // eslint-disable-line no-unused-vars
@@ -150,10 +150,22 @@ export default function gramps({
     }, extra);
   };
 
-  return req => ({
+  return {
     schema,
-    context: getContext(req),
+    context: getContext,
+    addContext: (req, res, next) => {
+      req.gramps = getContext(req);
+      next();
+    },
     // formatError: formatError(logger),
     ...apolloOptions.graphqlExpress,
+  };
+}
+
+export default function gramps(...args) {
+  const options = prepare(...args);
+  return req => ({
+    ...options,
+    context: options.context(req),
   });
 }

src/index.js

@@ -1,3 +1,4 @@
 import gramps from './gramps';
 
+export { prepare } from './gramps';
 export default gramps;

test/gramps.test.js

@@ -1,12 +1,23 @@
 import { GraphQLSchema } from 'graphql';
 import * as GraphQLTools from 'graphql-tools';
-import gramps from '../src';
+import gramps, { prepare } from '../src';
 
 describe('GrAMPS', () => {
   beforeEach(() => {
     jest.clearAllMocks();
   });
 
+  describe('prepare()', () => {
+    it('addContext() adds gramps property to request object', () => {
+      const { addContext } = prepare();
+      const next = jest.genMockFn();
+      const req = {};
+      addContext(req, {}, next);
+      expect(req).toEqual({ gramps: {} });
+      expect(next).toBeCalled();
+    });
+  });
+
   describe('gramps()', () => {
     it('creates a valid schema and empty context with no arguments', () => {
       const getGrampsContext = gramps();