Statistics API

The application exposes restful API for statistics. The main use case for the API is to calculate realtime statistic from the last 60 seconds. There will be two APIs, one of them is called every time a transaction is made. It is also the sole input of this rest API. The other one returns the statistic based of the transactions of the last 60 seconds.

Specs

POST /transactions

Every Time a new transaction happened, this endpoint will be called.

Body:

{
"amount": 12.3,
"timestamp": 1478192204000
}

Where:

• amount - transaction amount
• timestamp - transaction time in epoch in millis in UTC time zone (this is not current timestamp)

Returns: Empty body with either 201 or 204.

• 201 - in case of success
• 204 - if transaction is older than 60 seconds

Where:

• amount is a double specifying the amount
• time is a long specifying unix time format in milliseconds

GET /statistics

This is the main endpoint, this endpoint executes in constant time and memory (O(1)). It returns the statistic based on the transactions which happened in the last 60 seconds.

Returns:

{
"sum": 1000,
"avg": 100,
"max": 200,
"min": 50,
"count": 10
}

Where:

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

Requirements

For the rest api, the requirement is to make the GET /statistics execute in constant time and space.