[FEAT] Implement API Endpoint for Sending Email Requests

Description

Develop an endpoint to handle requests for sending emails using pre-defined templates. The emails should be placed in a database queue for sending to ensure the application remains responsive. The endpoint should handle variable substitution, replacing placeholders in the templates with actual data.

Acceptance Criteria

The endpoint should receive requests to send emails using specific templates.
The endpoint should handle variable substitution to replace placeholders with actual data.
The email sending request should be stored in a database queue.
The endpoint should return appropriate status codes and responses based on the outcome of the request.
Endpoints should be correctly versioned.

Data Validation

Input Validation: Validate that template_id, recipient, and variables fields are provided and correctly formatted.
Output Validation: Ensure the response contains the correct status and message.
Authentication and Authorization
Authentication: Ensure the endpoint requires valid user authentication.
Authorization: Verify that the user has permission to send emails using the specified template.

Error Handling

Error Responses: Define error responses for scenarios such as missing template, invalid input, and internal server errors. Edge Cases: Consider edge cases such as template not found, invalid email format, and missing variables.

Performance and Security

Performance Considerations: Ensure the email request queuing system is efficient and does not degrade application performance. Security Concerns: Address security considerations such as data sanitization, input validation, and protection against injection attacks.

Documentation

API Documentation: Provide comprehensive API documentation for the endpoint, including request and response formats. Technical Notes: Include any additional technical notes or considerations for implementing the endpoint.

Testing Requirements

Unit Tests: Implement unit tests to verify the functionality of the endpoint.
Integration Tests: Develop integration tests to ensure the endpoint works correctly with other system components.
Dependencies and Impact
Dependencies: Identify any dependencies on other tasks or systems, such as the database queue implementation.
Impact Analysis: Assess the potential impact on other features or components of the application.

Requirements

Implement an API endpoint for sending emails using templates.
Handle variable substitution for placeholders in the email templates.
Store email sending requests in a database queue.
Handle unexpected errors and return the appropriate status codes.
Ensure endpoints are correctly versioned.
Expected Outcome
Users should be able to send requests to the backend to enqueue emails using templates.
Users should receive appropriate status codes and responses based on the outcome of the requests.
Emails should be queued for sending without blocking the main application flow.
Endpoints

[POST] /api/v1/send-email

Description: Enqueues an email request using a specified template.
Request Body:
{
  "template_id": 1,
  "recipient": "john.doe@example.com",
  "variables": {
    "name": "John Doe",
    "product": "Wireless Headphones",
    "order_number": 12345
  }
}
Success Response:
Status Code: 202 Accepted
Body:

{
  "message": "Email sending request accepted and is being processed in the background."
}
Error Responses:
Status Code: 500 Internal Server Error
Body:

{
  "error": "Internal server error."
}
status Code: 404 Not Found
Body:

{
  "error": "Template not found."
}
Status Code: 405 Method Not Allowed
Body:

{
  "error": "This method is not allowed."
}
Status Code: 400 Bad Request
Body:

{
  "error": "An invalid request was sent."
}

Testing

Test Scenarios Successful Email Sending Request

Ensure that the endpoint accepts a request to send an email using a template.
Verify that the response indicates the request is being processed in the background.
Confirm that the status code is 202 Accepted.
Template Not Found
Simulate a scenario where the specified email template ID does not exist.
Confirm that the response body contains an appropriate error message.
Confirm that the status code is 404 Not Found.
Internal Server Error
Simulate an internal server error to raise an exception.
Verify that the endpoint returns a 500 Internal Server Error status code.
Confirm that the response body contains an appropriate error message.
Invalid Method
Send a request using an invalid HTTP method (e.g., GET) to the endpoint.
Verify that the endpoint returns a 405 Method Not Allowed status code.
Confirm that the response body contains an appropriate error message.
Bad Request
Send a request with invalid data (e.g., missing required fields) to the endpoint.
Verify that the endpoint returns a 400 Bad Request status code.
Confirm that the response body contains an appropriate error message.

hngprojects / hng_boilerplate_csharp_web