ShaneNolan / mastercard-solution

MasterCard technical interview solution.

Mastercard Technical Evaluation (Bin Range Application)

Preamble

BIN (Bank Identification Number) Ranges are used to provide information such as issuer currency code, bank name along with other relevant information for a given PAN (Primary account number) In Mastercard we often use BIN Ranges for enriching our decision making capabilities. It is therefore essential to have an up to date copy of the latest BIN Range information.

This application provides a HTTP REST interface for retrieving BIN Range info for a given PAN. BIN Ranges are loaded from a file on disk which is updated on a fixed schedule. This file is then stored in a simple cache so as to provide fast lookup for the HTTP interface.

Prerequisites

You will need the following installed on your development machine:

• Java 8
• Git
• Maven 3

Please clone this repository to your local workspace and develop your solution on a feature branch. When finished submit a single merge request containing all your changes.

N.B) if you want to clone the project using SSH you will need to add you public key to your gitlab profile, alternatively you can clone the project using HTTPS

The Challenge

• Your challenge will be broken down in to 3 parts of varying difficulty. Try to complete ALL parts.
• Please focus on the basics like ensuring you write good unit tests and perform data validation.
• Please rad through all instructions fully to ensure you understand what deliverables are expected.
• Your solution will be assessed based on your relevant skills and experience.

N.B. Important Instruction: Please complete ALL parts

Part 1. Approximately 20 minutes

We have recently pushed some code to the repository which seems to have broken a unit test This unit test has since been marked as ignored to fix the build temporarily. Your job is to fix the functionality according to the failing test cases in CachingBinRangeServiceTest.java. You can assume that the BIN Ranges do not change, however the data they refer to I.E. Bank Name and Currency Code can change You should also expect that a BIN Range can be removed from the cache.

N.B. The test should not be modified however additional tests would be welcomed to ensure this functionality does not break again.

Part 2. Approximately 50 minutes

Update the existing BinRangeInfoCacheController.java controller to add additional endpoints to handle the CREATE, UPDATE and DELETE actions on the BIN Range cache entries in case we need to modify the cache in between the scheduled period whereby the cache is refreshed from the file.

The endpoints should handle the cache entries individually I.E. this is not a batch API, Please note that a range start and end cannot change however the data they refer to can also there is the possibility of sub ranges I.E. a range that fits within a wider range however no ranges should share a start or end.

The CREATE endpoint should take a JSON representation of a BinRangeInfo.class in the body, please note the ref is generated on the server side The UPDATE endpoint should take a JSON representation of a BinRangeInfo.class in the body and the ref as a path param. The DELETE endpoint should take the ref associated with the desired BinRangeInfo.class entry in the cache as a path param, please ensure the index gets updated also.

Please ensure to create / update any relevant test cases to verify this new functionality,

Part 3. Approximately 50 minutes

We have recently received a new requirement to maintain an audit log for all changes to the cache for historical audit and debugging purposes. Some of the work for this has already been completed with the creation of the EventManager.java and the AuditSubscriber.java this event bus will be used to asynchronously update the audit log. It is your task to complete the functionality of this audit log to match the requirement in the JavaDoc found at AuditSubscriber.handleEvent() please ensure to have this functionality covered by adequate unit tests.

The Deliverable

Please ensure that this code is buildable by running mvn clean install and the application runs successfully with java -jar target/mastercard-evaluation-bin-range-application-0.0.1-SNAPSHOT.jar

• Please include documentation in SOLUTION.md about your approach and any assumptions you may have made while completing the above steps.
• Please include sample curl requests in your SOLUTION.md for each endpoint you develop.
• Create one Merge Request containing your changes for all of your work and notify the hiring manager by email when it is ready for review.

References

• How to create a Merge Request

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Solution

Part 1

Utilizing the debugger I set a breakpoint at the failing test and followed changes/loadings made to variables (besides trying to get head around Spring after sometime... 😅 ).

Both Pans 4319000000000001 and 5432000000000001 are loaded from the "bin-range-info-data.json" file on lines 61-63 in the CachingBinRangeService class, thus these tests should not fail.

Additionally Pans 4263000000000001 and 5263000000000001 are loaded via the getLatestBinRangeInfo function within the test file, thus cachingBinRangeService should not return null, these tests are working as expected.

I added an addition Pan to test (confirm) that cachingBinRangeService will return null when a Pan cannot be found (or when its removed from the cache.. I could have implemented functionality but that seemed overkill so this test will suffice). 🙌

---

Part 2

BinRangeService interface updated to define service logic functions - coupled to BinRangeInfo. I modified the BinRangeInfoCacheController to be loosely coupled by using the BinService interface instead of its actual implementation. Every test was created using Test Driven Development principles.

Examples are using HTTPie instead of curl (I messed around with my curl settings and never changed them back 😑).

Endpoints

GET

Not required but I implemented it for my own testing.

Example Usage

http GET http://localhost:8080/binRangeInfoCache/

HTTP/1.1 200
Content-Type: application/json;charset=UTF-8
Date: Sun, 25 Jul 2021 16:50:12 GMT
Transfer-Encoding: chunked

{
    "2a480c8a-83ca-4bb7-95b7-f19cec97b3fd": {
        "bankName": "AIB",
        "currencyCode": "EUR",
        "end": 4263999999999999,
        "ref": "2a480c8a-83ca-4bb7-95b7-f19cec97b3fd",
        "start": 4263000000000000
    },
    "7decd7db-1e93-4a44-beb9-d71e277a8239": {
        "bankName": "TSB",
        "currencyCode": "GBP",
        "end": 5432999999999999,
        "ref": "7decd7db-1e93-4a44-beb9-d71e277a8239",
        "start": 5432000000000000
    },
    "d893d80c-e7cf-4ba7-9f26-ae289d29e136": {
        "bankName": "BOI",
        "currencyCode": "USD",
        "end": 4319999999999999,
        "ref": "d893d80c-e7cf-4ba7-9f26-ae289d29e136",
        "start": 4319000000000000
    }
}

---

POST

Edge Cases

• If the Bin Range already exists.
• Data Validation.
• Ref can be supplied but it will be replaced with the server side generated ref.
• If the BinRange already exists.

Assumptions

• Data Validation: start, end, bankName and currencyCode cannot be null values. Ref can be null since its generated on the server side and if it is provided its overridden.

Responses

201

http POST http://localhost:8080/binRangeInfoCache start=1111000000000000 end=1111999999999999 bankName=test currencyCode=EUR

HTTP/1.1 201
Content-Type: application/json;charset=UTF-8
Date: Sun, 25 Jul 2021 16:35:17 GMT
Transfer-Encoding: chunked

{
    "bankName": "test",
    "currencyCode": "EUR",
    "end": 1111999999999999,
    "ref": "846c552e-fad0-411a-b3c4-a91b692cf0d4",
    "start": 1111000000000000
}

409

http POST http://localhost:8080/binRangeInfoCache start=1111000000000000 end=1111999999999999 bankName=test currencyCode=EUR

HTTP/1.1 409
Content-Length: 66
Content-Type: application/json;charset=UTF-8
Date: Mon, 26 Jul 2021 14:05:06 GMT

BinRangeInfo: 846c552e-fad0-411a-b3c4-a91b692cf0d4 already exists.

---

PUT

Edge Cases

• Start and End range cannot be modified.
• The path variable i.e. ref and Bin Range ref should match (not a business requirement but its best for validation).
• If the BinRange requested to update doesnt exist.

Assumptions

• Since a ref needs to be provided via a PathVariable and the json payload i.e. BinRangeInfo also provides a ref value they need to match. You could implement logic to set the json payload ref if its not provided but I think its best the user also provides it to ensure the correct BinRange is being updated. If the refs dont match a BinRangeInfoInvalidException is thrown.

• The start and end range cannot be modified once inserted. If they dont a BinRangeInfoInvalidException is thrown.

• Data Validation.

Responses

200

http PUT http://localhost:8080/binRangeInfoCache/2a480c8a-83ca-4bb7-95b7-f19cec97b3fd ref=2a480c8a-83ca-4bb7-95b7-f19cec97b3fd start=4263000000000000 end=4263999999999999 currencyCode=EUR bankName=AIB_TEST

HTTP/1.1 200
Content-Type: application/json;charset=UTF-8
Date: Mon, 26 Jul 2021 14:14:51 GMT
Transfer-Encoding: chunked

{
    "bankName": "AIB_TEST",
    "currencyCode": "EUR",
    "end": 4263999999999999,
    "ref": "2a480c8a-83ca-4bb7-95b7-f19cec97b3fd",
    "start": 4263000000000000
}

409

http PUT http://localhost:8080/binRangeInfoCache/2a480c8a-83ca-4bb7-95b7-f19cec97b3fd ref=846c552e-fad0-411a-b3c4-a91b692cf0d4 start=1263000000000000 end=1263999999999999 currencyCode=EUR bankName=AIB

HTTP/1.1 409
Content-Length: 99
Content-Type: application/json;charset=UTF-8
Date: Mon, 26 Jul 2021 14:09:57 GMT

Ref values 2a480c8a-83ca-4bb7-95b7-f19cec97b3fd : 846c552e-fad0-411a-b3c4-a91b692cf0d4 don't match.

404

http PUT http://localhost:8080/binRangeInfoCache/9651794E-8166-423F-8B8D-EE235A04DDB7 ref=9651794E-8166-423F-8B8D-EE235A04DDB7 start=5263000000000000 end=5263999999999999 currencyCode=EUR bankName=invalid

HTTP/1.1 404
Content-Length: 65
Content-Type: application/json;charset=UTF-8
Date: Mon, 26 Jul 2021 14:18:13 GMT

BinRangeInfo: 9651794e-8166-423f-8b8d-ee235a04ddb7 was not found.

409

http PUT http://localhost:8080/binRangeInfoCache/2a480c8a-83ca-4bb7-95b7-f19cec97b3fd ref=2a480c8a-83ca-4bb7-95b7-f19cec97b3fd start=4263000000000000 end=4263999999999990 currencyCode=EUR bankName=AIB

HTTP/1.1 409
Content-Length: 30
Content-Type: application/json;charset=UTF-8
Date: Mon, 26 Jul 2021 14:15:55 GMT

Bin Ranges cannot be modified.

---

DELETE

Edge Cases

• If the BinRange requested to be deleted doesnt exist.

Responses

200

http DELETE http://localhost:8080/binRangeInfoCache/846c552e-fad0-411a-b3c4-a91b692cf0d4

HTTP/1.1 200
Content-Type: application/json;charset=UTF-8
Date: Mon, 26 Jul 2021 14:20:27 GMT
Transfer-Encoding: chunked

{
    "bankName": "test",
    "currencyCode": "EUR",
    "end": 1111999999999999,
    "ref": "846c552e-fad0-411a-b3c4-a91b692cf0d4",
    "start": 1111000000000000
}

404

http DELETE http://localhost:8080/binRangeInfoCache/9651794E-8166-423F-8B8D-EE235A04DDB7

HTTP/1.1 404
Content-Length: 65
Content-Type: text/plain;charset=UTF-8
Date: Mon, 26 Jul 2021 14:20:51 GMT

BinRangeInfo: 9651794e-8166-423f-8b8d-ee235a04ddb7 was not found.

Data Validation

The POST and PUT endpoints have simple data validation to ensure the correct data is being provided.

Example

http POST http://localhost:8080/binRangeInfoCache start=1111000000000000 end=1111999999999999 bankName=test

HTTP/1.1 400
Connection: close
Content-Type: application/json;charset=UTF-8
Date: Mon, 26 Jul 2021 14:22:40 GMT
Transfer-Encoding: chunked

{
    "error": "Bad Request",
    "errors": [
        {
            "arguments": [
                {
                    "arguments": null,
                    "code": "currencyCode",
                    "codes": [
                        "binRangeInfo.currencyCode",
                        "currencyCode"
                    ],
                    "defaultMessage": "currencyCode"
                }
            ],
            "bindingFailure": false,
            "code": "NotNull",
            "codes": [
                "NotNull.binRangeInfo.currencyCode",
                "NotNull.currencyCode",
                "NotNull.java.lang.String",
                "NotNull"
            ],
            "defaultMessage": "must not be null",
            "field": "currencyCode",
            "objectName": "binRangeInfo",
            "rejectedValue": null
        }
    ],
    "message": "Validation failed for object='binRangeInfo'. Error count: 1",
    "path": "/binRangeInfoCache",
    "status": 400,
    "timestamp": "2021-07-26T14:22:40.747+0000"
}

---

Part 3

I updated the Event interface to be generic so it can handle multiple different types of audit events (this violates the YAGNI but I'm positive if this was a solution in production a new type of audit event would eventually be required. AuditSubscriber was also updated to handle the modified Event interface.

I didnt implement tests for EventBus because they werent asked for but if I were too I'd mock EventBus and ensure register was called x times and for the publishAsync method called EventBus.post.

I added additional tests for AuditEvent, specifically its toString method to ensure its outputting the valid format for logs.

Example Log File

createdAt={Wed Jul 28 17:07:01 BST 2021}, before={BinRangeInfo: ref=31fde6df-b594-477c-af57-f436b0c04842, start=2398000000000000, end=2398999999999999, bankName=Rempel, Rempel and Rempel, currencyCode=BRL}, after={BinRangeInfo: ref=31fde6df-b594-477c-af57-f436b0c04842, start=8764000000000000, end=8764999999999999, bankName=Cartwright LLC, currencyCode=NGN}

Conclusion

Hopefully this solution suffices, it took me a while (a lot of Googling) to figure out how Spring works again along with Java's testing libraries but I got there in the end (; are a nuisance after using Python for so long) :).