Add boilerplate content till Jake's code is good to go

docs/source/tutorial/resolvers.md

@@ -7,9 +7,121 @@ It's time to finally leverage all the data sources logic in our graph's resolver
 
 <h2 id="data-sources">Call your data sources in resolvers</h2>
 
-In the previous section of this tutorial, two data source classes were created. We'll be able to access those data sources in our resolvers, however, we need
+In the previous section of this tutorial, two data source classes were created and passed as options to the `ApolloServer` constructor. We'll access those data sources in our resolvers soon!
 
-Create a `resolvers.js` file within the `src` directory.
+Resolver functions accepts four arguments:
+
+```js
+fieldName(parent, args, context, info) {
+ // implementation
+}
+```
+
+* **parent**: This is an object that contains the result returned from the resolver on the parent field.
+* **args**: This is an object that contains the field arguments specified in a query.
+* **context**: This is an object shared by all resolvers in a particular query, and is used to contain per-request state, including authentication information, dataloader instances, and anything else that should be taken into account when resolving the query.
+* **info**: This argument has information about the execution state of the query. Mostly used in advanced cases.
+
+Create a `resolvers.js` file in the `src` directory. Copy the code below and paste it in the file.
+
+```js
+module.exports = {
+  Query: {
+    launches: async (root, { pageSize = 20, after }, { dataSources }) => {
+      return dataSources.launchAPI.getAllLaunches();
+    },
+    launch: (root, { id }, { dataSources }) => {
+      return dataSources.launchAPI.getLaunchById({ launchId: id });
+    },
+    me: async (_, __, { dataSources, user: { email } }) => {
+      if (!email) return null;
+      return dataSources.userAPI.findOrCreateUser({ email });
+    },
+  },
+};
+```
+
+The code above shows the resolver functions for the `Query` type. Let's analyze it.
+
+The `launches` field in the schema's Query type has two arguments, `pageSize`, and `after` which are necessary for pagination. This is why they appear as the second argument in the `launches` resolver function as shown in the code above. `{ dataSources }` appear as the third argument because Apollo Server puts them on the context for every request.
+
+In the body of the `launches` async resolver function, a request is made to fetch all launches via the `getAllLaunches` method on the `LaunchAPI` data source.
+
+The `launch` async function takes in an `id` as the second argument which represents a `launchId`. A request is made to fetch a launch by calling the `getLaunchById` method of the `launchAPI` data source class.
+
+The `me` async function // Wait for the code to be stable.
+
+Copy the code below for the `Mutation` type and paste it just after the `Query` resolver functions in the file.
+
+```js
+module.exports = {
+  Query: {
+    ...
+  },
+  Mutation: {
+    bookTrip: async (root, { launchId }, { dataSources, user }) => {
+      return dataSources.userAPI.bookTrip({
+        userId: user.id,
+        launchId: launchId,
+      });
+    },
+    cancelTrip: async (root, { launchId }, { dataSources, user }) => {
+      return dataSources.userAPI.cancelTrip({
+        launchId: launchId,
+        userId: user.id,
+      });
+    },
+    login: async (root, { email }, { dataSources }) => {
+      const user = await dataSources.userAPI.findOrCreateUser({ email });
+      if (user) return new Buffer(email).toString('base64');
+      return false;
+    },
+  }
+}
+```
+
+// Explanation for Mutation resolver function here. Wait till we are sure of what we are doing in the context logic
+
+Copy the code below for the `Launch` type and paste it just after the `Mutation` resolver functions.
+
+```js
+module.exports = {
+  ...
+  ...
+  Launch: {
+    passengers: async (launch, _, { dataSources }) => {
+      const res = await dataSources.userAPI.getUsersByLaunch({
+        launchId: launch.id,
+      });
+      return res && res.length ? res : [];
+    },
+  },
+}
+```
+
+// Explanation for Launch resolver function here. Wait till we are sure of what we are doing in the context logic
+
+Copy the code below for the `User` type and paste it just after the `Launch` resolver function.
+
+```js
+module.exports = {
+  ...
+  ...
+  User: {
+    trips: async (_, __, { dataSources, user: { id } }) => {
+      // get ids of launches by user
+      const launchIds = await dataSources.userAPI.getLaunchIdsByUser({
+        userId: id,
+      });
+
+      if (!launchIds.length) return [];
+
+      // look up those launches by their ids
+      return (dataSources.launchAPI.getLaunchesByIds({ launchIds }) || []);
+    },
+  },
+}
+```
 
 <h2 id="write-query">Write a query in the playground</h2>