Money Transfer API Design | Dataford Interview Questions

Design and implement a RESTful API (including data model and the backing implementation) for money transfers between accounts. Any framework could be used except Spring; the code should be workable and testable and with proper UT.

Asked in the take-home assignment stage. one week to submit.

For grading, implement transfer(accounts, source_account, destination_account, amount, idempotency_key, processed_keys). accounts maps account IDs to {balance: integer} objects. Return {status: integer, body: object} and mutate balances only for successful transfers. Reusing an idempotency key with the same request returns the saved response; reusing it with different parameters returns 409.

Example: transferring 250 from Alice with 1,000 to Bob with 500 returns status 201 and balances 750 and 750. Insufficient funds return 409 without mutation.

Constraints

accounts contains distinct string account IDs
Each account has an integer balance that is at least 0
amount is an integer
A successful transfer must have a positive amount
The source and destination accounts must be different
processed_keys maps an idempotency key to [request_list, response_object]

Function Signature

def transfer(accounts, source_account, destination_account, amount, idempotency_key, processed_keys):

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