(backend) Feat/link audit

[gweiying]

Problem

We want to provide an audit trail for link creators, so that they can know who has changed what on their link, and when.

See Notion story for details on user journey.

We currently store this data in our url_histories table. We parse the url records and expose an endpoint for the frontend to retrieve the records.

Solution

• Add repository layer to retrieve url records
• Add service layer to parse url records to return pairwise change sets
• Add controller and exposes endpoint /api/link-audit

For authenticated query:

GET /api/link-audit?url=<shortUrl>&limit=10&offset=10

Returns: (JSON) HttpStatus 200 for success

{
  changes: [ // ordered from most recent
    {
      "type": "update",
      "key": "state",
      "prevValue": "ACTIVE",
      "currValue": "INACTIVE",
      "updatedAt": "2022-04-06 09:15:26.272+00",
    },
    {
      "type": "update",
      "key": "longUrl",
      "prevValue": "https://google.com",
      "currValue": "https://twitter.com",
      "updatedAt": "2022-03-01 13:59:01.341+00',
    },
    {
      "type": "create",
      "key": "longUrl",
      "prevValue": "",
      "currValue": "https://abc.com",
      "updatedAt": "2022-01-30T04:45:55.204Z"
    }
  ],
  offset: 10, 
  limit: 10, 
  count: 13, // total count of results
}

changes is an array of type changeSets[]

Values:

• type (string): One of 'create', 'update'
• key (string): One of 'state','userEmail','longUrl'
• prevValue (string): string representation of previous key value
• currValue (string): string representation of current key value
• updatedAt

Refer to Notion doc for technical design.

Tests

What tests should be run to confirm functionality?

Future work

Improving pagination
We use the simplest approach to pagination currently (via limit and offset). There are various ways to improve this:

• primary-key-based offsets e.g. “where id < last_id_seen” in the query
• ORDER BY id rather than something like ORDER BY created_at

The rationale for these optimizations are documented in the Notion technical document - we can do these optimisations at a later date if we evaluate that this is a performance issue.

[yong-jie]

just dropping a quick ack here that i've started reviewing this PR, but will need a bit more time after the dust settles to finish 🙏

[yong-jie]

Nice work! PR looks functionally complete; i just have some minor nits you could consider addressing, and some things i'd to hear your thoughts on.

[yong-jie]

lgtm! feel free to merge when ready~