EXAPP

Objective

Build a market trade processor which consumes trade messages via an endpoint, processes those messages in some way and delivers a frontend of processed information based on the consumed messages.

Solution

The core of the provided solution is a RESTful API powered by a monolithic Laravel 4.2 app of layered architecture.

The API offers 2 resources:

• MESSAGES - a write only endpoint for storing message data
• COUNTRIES - a read only endpoint for accessing country statistics

The statistics are computed by the PROCESSOR service that is called by a CLI command.

The frontend is a separate component that fetches the statistics from the API and displays them.

For the purpose of this exercise the API does not include any authentication or authorization mechanisms.

The main accent of the solution is put on the following aspects:

API Design

The API operates in a RESTful manner and both of the available resources are self-discoverable (via OPTIONS request) and CORS-enabled. The API offers detailed error messages and appropriate HTTP status codes accounting for different situations (success, validation failure, errors etc.).

Extensibility

The application structure is designed with SOLID principles in mind and uses PSR-4 autoloading. The code is PSR-1/2 compliant and thoroughly commented (PHPDoc).

Testing

The solution is developed in StoryBDD style, thus the main functionalities (MESSAGES endpoint, COUNTRIES endpoint and the PROCESSOR) are shaped and verified by Behat tests (30 scenarios/65 steps).

Most of Exapp specific classes have corresponding PHPUnit test cases (55 tests/55 assertions) providing 88% code coverage.

Commits and pull requests are built and unit tested with Travis-CI whereas the coverage is calculated with Coveralls service.

Components

Message Consumption

The consumption endpoint is located under the MESSAGES resource and accepts data in JSON format as body of a POST request.

http://exapp-base-url/v1/messages

Example input:

{
	"userId": "134256", 
	"currencyFrom": "EUR", 
	"currencyTo": "GBP", 
	"amountSell": 1000, 
	"amountBuy": 747.10, 
	"rate": 0.7471, 
	"timePlaced" : "24­-JAN-­15 10:27:44", 
	"originatingCountry" : "GB"
}

Data posted to the endpoint is validated and upon passing validation it is stored in a MySql (or alternatively SQLite) database. The allowed countries of origin and currencies are defined in the following config file:

/exapp-installation-path/app/config/exapp.php

Message Processor

The PROCESSOR calculates message statistics grouped by country of origin for all received and stored messages, offering the following per country metrics:

• Total message count
• Top currency pair
• Top currency pair message count
• Top currency pair average exchange rate
• The share of top currency pair’s messages in the total volume of messages (represented as percentage)

The PROCESSOR service is run as a separate process in form of a Laravel Artisan command that is invoked in CLI every 1 minute with CRON. The command can of course be executed manually by running

php /exapp-installation-path/artisan exapp:process

The calculated statistics are available in JSON format under the COUNTRIES resource and can be fetched via a GET request.

http://exapp-base-url/v1/countries

Example output:

{
    "data":[
        {
            "countryCode":"DE",
            "countryName":"Germany",
            "messageCount":6,
            "topCurrencyPair":"EUR\/CHF",
            "topCurrencyPairMsgCnt":3,
            "topCurrencyPairAvgRate":0.7471,
            "topCurrencyPairMsgShare":"50%"
        },
        {
            "countryCode":"CH",
            "countryName":"Switzerland",
            "messageCount":3,
            "topCurrencyPair":"EUR\/CHF",
            "topCurrencyPairMsgCnt":2,
            "topCurrencyPairAvgRate":0.7471,
            "topCurrencyPairMsgShare":"66.67%"
        }
    ]
}

Message Frontend

The frontend component is a static HTML page that upon loading fetches the precomputed message statistics (using a jQuery AJAX call) from the COUNTRIES resource and plots them on a world map (via Google GeoChart API).

http://exapp-base-url/frontend.html

The colour of each country corresponds to the ‘Total message count’ metric whereas detailed statistics are displayed in a tooltip upon hovering the mouse cursor over the area of a country (only if there were any messages originating from that country). The map can be manually refreshed by pressing the ‘Refresh chart’ button.