Problem: Fetch and Join Paginated Data from Multiple APIs

Implement a function, get_enriched_records(api_a_url, api_b_url), that retrieves and processes data from two distinct, paginated API endpoints.

API Endpoints

api_a_url

This endpoint returns paginated JSON data with the following structure:

{
  "data": [
    {"id": 1, "ref_id": "x1"},
    {"id": 2, "ref_id": "x2"}
  ],
  "next_page": 2 // Or null if no more pages
}

api_b_url

This endpoint also returns paginated JSON data, structured as follows:

{
  "data": [
    {"ref_id": "x1", "target_field": "value1"},
    {"ref_id": "x2", "target_field": "value2"}
  ],
  "next_page": null // Or a page number if more pages
}

Requirements

The get_enriched_records function must fulfill the following criteria:

1. Full Retrieval: Fetch all available pages from both api_a_url and api_b_url.
2. Data Joining: Join records from the two APIs based on their common ref_id field.
3. Output Format: Return a list of objects, each structured as { "id": <id>, "target_field": <value> }.
4. Order Preservation: The order of the final enriched records must correspond to the original order of records retrieved from api_a_url.
5. Record Filtering: Skip any record from api_a_url if any of the following conditions are met:
   • The ref_id field is missing from the api_a_url record.
   • No matching record exists in the data retrieved from api_b_url for the given ref_id.
   • The target_field in the matched api_b_url record is null, an empty string, or consists solely of whitespace characters.
6. Robustness: Implement defensive programming to safely handle potential issues such as missing keys in JSON objects, empty data pages, or None values without causing the function to crash.
7. HTTP Handling: Use standard HTTP request mechanisms. Assume that the API responses will be mocked by the test harness, so actual network calls are not the focus.

The primary evaluation criteria will be the clarity of API retrieval logic, effective pagination handling, and robust data validation, rather than advanced algorithmic complexity.