Asset Statuses

Considering IoT most of the modern plants or production facilities these days are equipped with a large number of sensors that send various data about certain assets or processes of the plant. In our fictional plant, we have thousands of sensors that dispatch statuses of assets via messages to some "real-time queue". This fictional queue emits millions of asset status messages per second and for each message, it calls the handle(Message message) function of a message processor(s) attached to it.

NOTE: you are not expected to implement the above-mentioned "real-time queue".

An asset status can be of a NORMAL, WARNING or ERROR types. A typical asset status message has the following payload:

{
  "id": "4fda181e-c9c7-4d68-8e31-f9a42dd33aa8",       // status message UUID
  "assetId": "8ed2b7ac-fbc5-4afe-ba77-4105459fdd2d",  // UUID of asset being reported on
  "statusType": "NORMAL",                             // one of NORMAL, WARNING, ERROR status types
  "createdAt": "2018-10-22T09:43:00.862Z"             // ISO 8601 UTC DateTime when status was reported
}

You're required to implement a system that provides a simple API to do the following:

• Allow its consumers to subscribe to certain asset status events and notify them about those events:
  • AssetMayFail event should be emitted when asset status changed to WARNING
  • AssetFailed event should be emitted when asset status changed to ERROR
  • AssetRecovered event should be emitted when asset status is changed back to NORMAL NOTE: if the newly arrived status message did not result in the status change for the asset there should be no events emitted.
• Store asset statuses in such a way to be able to do the following queries without incurring performance penalty (i.e. due to a large number of assets or statuses):
  • Return the current (i.e. latest) asset status by a given asset id
  • Return asset ids for a given status type. For example: show me all assets that are currently failed (i.e. have ERROR status).

Input:

Use the provided asset_statuses.json file containing 1000 asset status messages in JSON format as an input. Your solution will be tested by running from the shell and passing the JSON file through an argument. For example:

 $ > java YourSolution asset_statuses.json
 // or
 $ > node YourSolution.js asset_statuses.json

Output:

The main() function of your solution should process the JSON input file and mock a real-time queue by calling for each incoming message the handle(Message message) function of the system that you will implement. As your solution processes the incoming messages it should report the events and result in the following output in stdout:

• Any status changes for assets for example:

  ...
  Asset 67247f96-1b1a-48e5-82b4-5277d4438b3c is about to fail with status WARNING at 2011-01-03T01:41:48Z
  // here the asset status changed to ERROR from the WARNING status
  Asset 67247f96-1b1a-48e5-82b4-5277d4438b3c has eventually failed with status ERROR at 2011-07-14T18:42:46Z
  // here the asset status changed to ERROR from the NORMAL status without a WARNING
  Asset 8786cc43-230d-4ac9-8827-5287f4bfa7d8 has abruptly failed with status ERROR at 2011-07-14T18:42:46Z
  Asset 67247f96-1b1a-48e5-82b4-5277d4438b3c has recovered with status NORMAL at 2012-02-16T11:27:28Z
  ...
  

  NOTE: the above inline // comments are for explanation and are not expected in the output.

After all the messages have been processed the main() function should also:

• Get current asset statuses by asset ids for the following assets:

  f1aa3b54-6238-4e67-b3ea-a5bc13b77dd0,
  fbbcaf29-a72f-48f7-8f2b-d5abf8bc24bf,
  4f436a0d-903b-46bd-8e45-46c1dd3dc631
  

  And should print the following in stdout:

  Current status for asset 'f1aa3b54-6238-4e67-b3ea-a5bc13b77dd0' is 'ERROR'
  Current status for asset 'fbbcaf29-a72f-48f7-8f2b-d5abf8bc24bf' is 'NORMAL
  Current status for asset '62d98170-ff7e-4ee1-8f1c-b54f8aed351c' is 'WARNING'
  

• Get asset ids by status type ERROR and should print the following in stdout:

  There are 2 assets which currently have an ERROR status:
  'f1aa3b54-6238-4e67-b3ea-a5bc13b77dd0',
  '18a5ba9a-7a0f-4c09-a836-8e2ef2da79ca'
  

• Get asset ids by status type WARNING and should print the following in stdout:

  There are 10 assets which currently have a WARNING status:
  '67247f96-1b1a-48e5-82b4-5277d4438b3c',
  '62d98170-ff7e-4ee1-8f1c-b54f8aed351c',
  '12a594e4-f51f-407e-9d01-679a8323a3c0',
  '8fded256-979f-402c-aacc-8ab6b98787d1',
  '8786cc43-230d-4ac9-8827-5287f4bfa7d8',
  '4f436a0d-903b-46bd-8e45-46c1dd3dc631',
  '5cd0c05f-2a39-4ea5-b0ea-0dedb3e5b968',
  '91acbf58-e7ea-4790-b58a-7442d2a32109',
  'e4c52414-9776-451d-ba80-f3f46b77686b',
  'd4250e33-f81f-408f-855a-36414fe4cee5'
  

Assumptions/Expectations:

• For brevity assume that storing of asset statuses using in-memory data structures should be sufficient. (i.e. no need for DB)
• You can use the programming language of your choice.
• You can use the programming paradigm of your choice (i.e. OOP, functional, etc.)
• You should not need to use any framework for this exercise.
• The provided solution should be executable when you feed it the mock data file asset_statuses.json
• Bonus points if you provide unit tests along with your implementation.

Submit your solution by forking this repository and creating a Pull Request on GitHub. This will allow our developers to provide comments to your proposed solution.