Transaction Statistics

This is a RESTful API to hold transactions and provide realtime statistics for the last 60 seconds.

API endpoints

POST /transactions

This endpoint is called to create a new transaction.

Request:

{
  "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 executes in constant time and memory (O(1)).

Response:

{
  "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.

Build Instructions

This API runs using REDIS storage, so you'll need to have a redis server running. To install redis, simply run sudo apt-ge install redis on a linux or wsl terminal.

Install Packages

npm i

Run redis Server

on a seprate linux or wsl terminal, startup the redis server

redis-server

Run nodejs server

npm run dev

Rate Limit

There's a rate limit of 120 POST requests/min to the /transaction endpoint from the same IP address

The application listens on port 3000 by default.