From 0ea68438323aa3894a5e8b500562988cec514af9 Mon Sep 17 00:00:00 2001
From: DavidC <david@dchere.com>
Date: Wed, 29 Nov 2017 18:48:24 +0100
Subject: [PATCH] feat(contextware for dataloaders): added kind of middleware
 that is run on each operation to initial

---
 README.md              | 14 ++++++++++----
 src/bridgeLink.js      | 18 ++++++++++++++++--
 src/bridgeLink.test.js | 19 ++++++++++++++++++-
 3 files changed, 44 insertions(+), 7 deletions(-)

diff --git a/README.md b/README.md
index ef5b1a9..400d636 100644
--- a/README.md
+++ b/README.md
@@ -53,18 +53,24 @@ import { InMemoryCache } from 'apollo-cache-inmemory';
 import schema from './schema';
 
 // your resolvers (see example)
-import reolvers from './resolvers';
+import resolvers from './resolvers';
 
 // if you want to mock anything in the schema (that has not resolver or doesn't return data)
 const mock = true;
 
 // if you want to push something down to the resolvers in context
 const context = {
-  graphQl: 'is cool'
-}
+  graphQl: 'is cool',
+};
+
+// do something with actual context and operation of gql operation
+// and return object that will be shallow merged to context
+// use for init dataloader with token for example
+// see example... https://github.com/dacz/apollo-bridge-link-example
+const contextware = (ctx, operation) => ({ inContext: 'from contextware' });
 
 export const client = new ApolloClient({
-  link: BridgeLink({ schema, resolvers, mock, context });
+  link: BridgeLink({ schema, resolvers, mock, context, contextware });
   cache: new InMemoryCache({ addTypename: true }),
 });
 ```
diff --git a/src/bridgeLink.js b/src/bridgeLink.js
index e2f2eb0..737fb23 100644
--- a/src/bridgeLink.js
+++ b/src/bridgeLink.js
@@ -4,7 +4,13 @@ import { addMockFunctionsToSchema, makeExecutableSchema } from 'graphql-tools';
 import { ApolloLink } from 'apollo-link';
 import Observable from 'zen-observable';
 
-export const createBridgeLink = ({ schema, resolvers, mock, context = {} }) => {
+export const createBridgeLink = ({
+  schema,
+  resolvers,
+  mock,
+  context = {},
+  contextware = [],
+}) => {
   let executableSchema;
   if (typeof schema === 'string') {
     executableSchema = makeExecutableSchema({ typeDefs: schema, resolvers });
@@ -31,12 +37,20 @@ export const createBridgeLink = ({ schema, resolvers, mock, context = {} }) => {
     operation =>
       new Observable(observer => {
         const { headers, credentials } = operation.getContext();
-        const ctx = {
+        const ctxInitial = {
           ...context,
           headers,
           credentials,
         };
 
+        // contextware
+        const ctx = [].concat(contextware).reduce((acc, fn) => {
+          const rv = fn(acc, operation);
+          return typeof rv === 'object' && !Array.isArray(rv)
+            ? { ...acc, ...rv }
+            : acc;
+        }, ctxInitial);
+
         graphql(
           executableSchema,
           print(operation.query),
diff --git a/src/bridgeLink.test.js b/src/bridgeLink.test.js
index be571fa..3cc02c1 100644
--- a/src/bridgeLink.test.js
+++ b/src/bridgeLink.test.js
@@ -86,6 +86,23 @@ test('BridgeLink mocks data', async t => {
   t.truthy(res.data.posts[0].author.id, 'should have mocked author');
 });
 
+test('BridgeLink calls contextware', async t => {
+  const returning = { middle: 'data' };
+  const init = sinon.mock().returns(returning);
+  const opts = {
+    schema: schemaExample,
+    mock: true,
+    contextware: init,
+  };
+  const link = new BridgeLink(opts);
+  const cache = new InMemoryCache();
+  const client = new ApolloClient({ link, cache });
+  const res = await client.query({ query: POSTS });
+  t.true(res.data.posts.length > 0, 'should get some mocked data');
+  t.truthy(res.data.posts[0].author.id, 'should have mocked author');
+  t.true(init.calledOnce);
+});
+
 test('BridgeLink should accept executable schema', async t => {
   const posts = [
     {
@@ -170,7 +187,7 @@ test('createBridgeLink - creates link', t => {
   const schema = schemaExample;
   const resolvers = {};
   const mock = false;
-  const context = {};
+  const context = { gq: 'is cool' };
   const link = createBridgeLink({ schema, resolvers, mock, context });
   t.true(link instanceof ApolloLink);
 });