nbp-php

API for accessing Polish National Bank (NBP - Narodowy Bank Polski) currency and commodities exchange rates.

Installing via composer

composer require maciej-sz/nbp-php

Usage

The full API of this library can be found in api.md.

Minimal setup

<?php
require_once 'vendor/autoload.php';

use MaciejSz\Nbp\Service\CurrencyAverageRatesService;

$currencyAverages = CurrencyAverageRatesService::new();
$rate = $currencyAverages->fromDay('2023-01-02')->fromTable('A')->getRate('USD');

printf('%s rate is %d', $rate->getCurrencyCode(), $rate->getValue());

USD rate is 4.381100

Examples

See the examples directory for complete and runnable examples.

Using cache

Note that a library implementing PSR-6 has to be provided in order to use the caching abilities.

The CachedTransport class is a proxy for all other transport implementations. This transport has to be backed by another transport, as it relies on it to make the actual requests that have not been cached yet.

Example

use Symfony\Component\Cache\Adapter\FilesystemAdapter as CachePoolAdapter;

// 1) create repository backed by caching transport
$cachePool = new CachePoolAdapter();
$cachingTransportFactory = CachingTransportFactory::new($cachePool);
$client = NbpWebClient::new(transportFactory: $cachingTransportFactory);
$nbpRepository = NbpWebRepository::new($client);

// 2) create needed services using cache-backed repository:
$goldRates = new GoldRatesService($nbpRepository);

// 3) run multiple times to check the effect of caching:
$start = microtime(true);
$goldRates->fromDayBefore('2013-05-15')->getValue();
$end = microtime(true);
$took = $end - $start;
printf('Getting the rate took %F ms', $took * 1000);

Using custom transport

The library uses Symfony HTTP Client and Guzzle as default transports. If those packages are not available then it falls back to the file_get_contents method. This may not be ideal in some situations. Especially when there is no access to HTTP client packages as may be the case when using PHP version prior to 8.0.

In such cases it is suggested to use different transport. It can be achieved by replacing the TransportFactory of the NbpClient with your own implementation.

$customTransportFactory = new class() implements TransportFactory {
    public function create(string $baseUri): Transport
    {
        return new class() implements Transport {
            public function get(string $path): array
            {
                echo "Requesting resource: {$path}" . PHP_EOL;

                $ch = curl_init();
                $url = NbpWebClient::BASE_URL . $path;
                curl_setopt($ch, CURLOPT_URL, $url);
                curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
                try {
                    $output = curl_exec($ch);
                } finally {
                    curl_close($ch);
                }

                echo 'Request successful' . PHP_EOL;

                return json_decode($output, true);
            }
        };
    }
};

$client = NbpWebClient::new(transportFactory: $customTransportFactory);
$nbpRepository = NbpWebRepository::new($client);
$goldRates = GoldRatesService::new($nbpRepository);

$rate = $goldRates->fromDay('2022-01-03');

printf(
    'Gold rate from %s is %F',
    $rate->getDate()->format('Y-m-d'),
    $rate->getValue()
);

Requesting resource: /api/cenyzlota/2022-01-01/2022-01-31
Request successful
Gold rate from 2022-01-03 is 235.720000

Architecture

On the infrastructure level the code utilizes layered architecture to keep the concerns separated.

Service layer

The service consists of facades for the package. Classes here are named services instead of facades due to common understanding of this word as something through which you access the internals of a system.

This layer provides a high level business-oriented methods for interacting with the NBP API. It exposes most common use cases of the nbp-php package and is the likely starting point for all applications using this package. One needs to interact with other layers only for more complex tasks.

The service layer is structured in the way that it directly communicates with the repository layer.

Repository layer

Repository layer allows getting data from NBP API by providing methods that closely reflect the NBP Web API. This layer operates on higher level, hydrated domain objects.

The only constraint here is that the repository layer operates on month-based dates. So for example you can get trading rates from entire month, but in order to retrieve a specific date you have to iterate through the retrieved month (you can use service layer for that). This is by design for the purpose of reducing network traffic to the NBP servers. It also allows simplifying caching on the transport layer, because there is no need for any cache-pooling logic.

Client layer

Client layer is a bridge between the repository and the transport layer. It processes request objects on the input, and then it uses the transport layer to fulfill those requests.

The requests thet client layer uses are higher-level requests then those on the transport layer. They implement NbpClientRequest interface.

Transport layer

The transport layer is responsible for directly interacting with the NBP API. A few independent transport implementations are provided for serving connections to the NBP API.

It is also equipped with a convenient factories which pick the most appropriate implementation depending on installed libraries and configuration.