Feat: newsletter's unsubscribe endpoint

[Heba-WebDev]

Description

Closes #404

Changes proposed

• Added POST /api/v1/news-letter/unsubscribe endpoint to Newsletter controller
• Created a command and a command handler in the Hng.Application project to handle the interface and logic of the endpoint
• Added unit tests for the command handler in the Hng.Application.Test project

Check List (Check all the applicable boxes)

• My code follows the code style of this project.
• This PR does not contain plagiarized content.
• The title and description of the PR is clear and explains the approach.
• I am making a pull request against the dev branch (left side).
• My commit messages styles matches our requested structure.
• My code additions will fail neither code linting checks nor unit test.
• I am only making changes to files I was requested to.

Screenshots/Videos

• Invalid email format returns a 400 status code
  

• Not found subscriber return 400 status code
  

• Successful response returns a 200 status code
  

• Tests passed
  

[samuelogboye]

Is there a subscribe endpoint?

[Heba-WebDev]

Yes, the subscribe endpoint is POST /api/v1/pages/newsletter. (On the issue I had PATCH as the method, but I changed it to POST to match what the other teams have)

[samuelogboye]

if Subscribe is /api/v1/news-letter POST
unsubscribe should be /api/v1/news-letter DELETE

[Heba-WebDev]

The dilemma is, we're asked to have a unified backend.

• Py team: have an identical endpoint to this one.
  pros: no need to call a GET endpoint to get the id
  cons: DELETE method is more accurate.
• Nestjs team: have DELETE /:id endpoint.
  pros: DELETE method is accurate.
  cons: the client now needs to call a GET endpoint to find the id and then call the DELETE endpoint.

What approach would be considered more RESTful? I'd like to know your opinion.

[samuelogboye]

.../news-letter POST for subscribe (add resource to db)
.../news-letter DELETE for unsubscribe (remove from db)

this is more RESTFUL

[samuelogboye]

Use .Trim().ToLower() to normalize the email before processing

[Heba-WebDev]

Noted

[samuelogboye]

Whats your thought on soft and hard delete?

[Heba-WebDev]

Both are needed, though soft delete is more common (for marketing, for archiving, for legal purposes etc).