How to do it...

1. Create the project from the following template:

$ sls create --template-url https://github.com/danteinc/js-cloud-native-cookbook/tree/master/ch2/materialized-view-cognito --path cncb-materialized-view-cognito

2. Navigate to the cncb-materialized-view-cognito directory with cd cncb-materialized-view-cognito.
3. Review the file named serverless.yml with the following content:

service: cncb-materialized-view-cognito

provider:
  name: aws
  runtime: nodejs8.10
  iamRoleStatements:
    ...

functions:
  listener:
    handler: handler.listener
    events:
      - stream:
          type: kinesis
          arn: ${cf:cncb-event-stream-${opt:stage}.streamArn}
          ...
    environment:
      IDENTITY_POOL_ID:
        Ref: IdentityPool

resources:
  Resources:
    IdentityPool:
      Type: AWS::Cognito::IdentityPool
      ...

  Outputs:
    identityPoolId:
      Value: 
        Ref: IdentityPool
    identityPoolName:
      Value: 
        Fn::GetAtt: [ IdentityPool, Name ]

4. Review the file named handler.js with the following content:

module.exports.listener = (event, context, cb) => {
  _(event.Records)
    .map(recordToEvent)
    .filter(forThingCreated)
    .map(toThing)
    .flatMap(put)
    .collect()
    .toCallback(cb);
};

...
const forThingCreated = e => e.type === 'thing-created';

const toThing = event => ({
  id: event.thing.new.id,
  name: event.thing.new.name,
  description: event.thing.new.description,
  identityId: event.thing.new.identityId, // the end user
  asOf: event.timestamp,
});

const put = thing => {
  const params = {
    IdentityPoolId: process.env.IDENTITY_POOL_ID,
    IdentityId: thing.identityId,
    DatasetName: 'things',
  };

  const cognitosync = new aws.CognitoSync();

  return _(
    cognitosync.listRecords(params).promise()
      .then(data => {
        params.SyncSessionToken = data.SyncSessionToken;
        params.RecordPatches = [{
          Key: 'thing',
          Value: JSON.stringify(thing),
          Op: 'replace',
          SyncCount: data.DatasetSyncCount,
        }];

        return cognitosync.updateRecords(params).promise()
      })
  );
};

5. Install the dependencies with npm install.
6. Run the tests with npm test -- -s $MY_STAGE.
   
7. Review the contents generated in the .serverless directory.
8. Deploy the stack:

$ npm run dp:lcl -- -s $MY_STAGE

> cncb-materialized-view-cognito@1.0.0 dp:lcl <path-to-your-workspace>/cncb-materialized-view-cognito
> sls deploy -v -r us-east-1 "-s" "john"

Serverless: Packaging service...
...
Serverless: Stack update finished...
...
functions:
  listener: cncb-materialized-view-cognito-john-listener

Stack Outputs
identityPoolName: IdentityPool_c0GbzyVSh3Ws
identityPoolId: us-east-1:3a07e120-f1d8-4c85-9c34-0f908f2a21a1
...

9. Review the stack, function, and identity pool in the AWS Console.
10. Update the file named index.html file with the identityPoolId from previous output.
11. Open the file named index.html in a browser and copy the identity ID for use in the next step.
    

12. Publish an event from a separate Terminal with the following commands:

$ cd <path-to-your-workspace>/cncb-event-stream
$ sls invoke -r us-east-1 -f publish -s $MY_STAGE -d '{"type":"thing-created","thing":{"new":{"name":"thing five","id":"55555555-5555-5555-5555-555555555555", "identityId":"<identityId from previous step>"}}}'

{
    "ShardId": "shardId-000000000000",
    "SequenceNumber": "49583655996852917476267784847452524471369889169788633090"
}

13. Take a look at the logs:

$ sls logs -f listener -r us-east-1 -s $MY_STAGE

START ...
2018-04-19 00:18:42 ... {"type":"thing-created","thing":{"new":{"name":"thing five","id":"55555555-5555-5555-5555-555555555555","identityId":"us-east-1:ee319396-fec4-424d-aa19-71ee751624d1"}},"id":"bda76e80-4388-11e8-a845-5902692b9264","partitionKey":"c9d4e9e5-d33f-4907-9a7a-af03710fa50f","timestamp":1524111521129,"tags":{"region":"us-east-1"}}
2018-04-19 00:18:42 ... params: {"IdentityPoolId":"us-east-1:3a07e120-f1d8-4c85-9c34-0f908f2a21a1","IdentityId":"us-east-1:ee319396-fec4-424d-aa19-71ee751624d1","DatasetName":"things"}
2018-04-19 00:18:43 ... {"Records":[{"Key":"thing","Value":"{\"id\":\"55555555-5555-5555-5555-555555555555\",\"name\":\"thing five\",\"asOf\":1524111521129,\"identityId\":\"us-east-1:ee319396-fec4-424d-aa19-71ee751624d1\"}","SyncCount":1,"LastModifiedDate":"2018-04-19T04:18:42.978Z","LastModifiedBy":"123456789012","DeviceLastModifiedDate":"2018-04-19T04:18:42.978Z"}]}
END ...
REPORT ... Duration: 340.94 ms    Billed Duration: 400 ms ... Max Memory Used: 33 MB    

14. Open the file named index.html in a browser and press the Synchronize button to retrieve the data from the materialized view:

15. Remove the stack once you have finished with npm run rm:lcl -- -s $MY_STAGE.