Transactions-Statistics evaluation

RESTful API for statistics. The main use case for the API is to calculate real time statistics for the last 60 seconds of transactions.

The API needs the following endpoints:

• POST /transactions – called every time a transaction is made.
• GET /statistics – returns the statistic based of the transactions of the last 60 seconds.
• DELETE /transactions – deletes all transactions.

Specs

POST: /transactions

This endpoint is called to create a new transaction. It MUST execute in constant time and memory (O(1)).

Body:
{
  "amount": "12.3343",
  "timestamp": "2018-07-17T09:59:51.312Z"
}

Where:

• amount – transaction amount; a string of arbitrary length that is parsable as a BigDecimal
• timestamp – transaction time in the ISO 8601 format YYYY-MM-DDThh:mm:ss.sssZ in the UTC timezone (this is not the current timestamp)

Returns: Empty body with one of the following:

• 201 – in case of success
• 204 – if the transaction is older than 60 seconds
• 400 – if the JSON is invalid
• 422 – if any of the fields are not parsable or the transaction date is in the future

GET: /statistics

This endpoint returns the statistics based on the transactions that happened in the last 60 seconds. It MUST execute in constant time and memory (O(1)).

Returns: { "sum": "1000.00", "avg": "100.53", "max": "200000.49", "min": "50.23", "count": 10 }

Where:

• sum – a BigDecimal specifying the total sum of transaction value in the last 60 seconds
• avg – a BigDecimal specifying the average amount of transaction value in the last 60 seconds
• max – a BigDecimal specifying single highest transaction value in the last 60 seconds
• min – a BigDecimal specifying single lowest transaction value in the last 60 seconds
• count – a long specifying the total number of transactions that happened in the last 60 seconds

All BigDecimal values always contain exactly two decimal places and use HALF_ROUND_UP rounding. eg: 10.345 is returned as 10.35, 10.8 is returned as 10.80

DELETE: /transactions

This endpoint causes all existing transactions to be deleted.

The endpoint should accept an empty request body and return a 204 status code.

SetUp Application

To Build: (Unit Test cases included) mvn clean install

To Run: spring-boot:run

To Run Integration tests: mvn clean failsafe:integration-test

Time Complexity

• ConcurrentHashMap used to achieve thread-safe & concurrent transactions from API requests. PUT/GET operations performed in constant time and memory O(1).