# Customizing Subscription Intervals

The B2Bsellers Suite allows you to extend or modify the available subscription intervals to meet specific business requirements. This is a two-step process: adding the interval to the collection and providing a processor to calculate future delivery dates.

## Adding or Removing Intervals

To modify the list of available intervals, create an event subscriber that listens to the `DeliveryIntervalCollectorEvent`.

Inside the subscriber, you can use the `getCollection()` method to remove existing intervals (like `weekly`) or add new ones using the `DeliveryIntervalStruct`.

### Example

{% code expandable="true" %}

```php
// <plugin root>/src/Subscriber/DeliveryIntervalSubscriber.php

namespace B2bSellersExample\Subscriber;

use B2bProductSubscription\Components\ProductSubscription\Events\DeliveryIntervalCollectorEvent;
use B2bProductSubscription\Components\ProductSubscription\Struct\DeliveryIntervalStruct;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Contracts\Translation\TranslatorInterface;

class DeliveryIntervalSubscriber implements EventSubscriberInterface
{
    public function __construct(private readonly TranslatorInterface $translator) {}

    public static function getSubscribedEvents(): array
    {
        return [
            DeliveryIntervalCollectorEvent::class => 'onChangeDeliveryIntervals'
        ];
    }

    public function onChangeDeliveryIntervals(DeliveryIntervalCollectorEvent $event): void
    {
        $collection = $event->getCollection();
        
        // Remove an existing interval
        $collection->remove('weekly');

        // Add a custom interval
        $key = 'custom';
        $collection->set($key, new DeliveryIntervalStruct(
            $key,
            $this->translator->trans('b2b-subscription.interval.' . $key),
            'b2b-subscription.interval.' . $key
        ));
    }
}
```

{% endcode %}

## Implementing the Interval Processor

For every custom interval added, you must provide a corresponding processor to calculate the next delivery or order date.

The processor must implement the `IntervalProcessorInterface` and be registered in the service container with a specific the `b2b_product_subscription.interval.processor` tag.

### Example

{% code expandable="true" %}

```php
// <plugin root>/src/ProductSubscription/DeliveryInterval/Processor/CustomIntervalProcessor.php

namespace B2bSellersExample\ProductSubscription\DeliveryInterval\Processor;

use B2bProductSubscription\Components\ProductSubscription\DeliveryInterval\Processor\IntervalProcessorInterface;

class CustomIntervalProcessor implements IntervalProcessorInterface
{
    public const DELIVERY_KEY = 'custom';

    public function isSupported(string $key): bool
    {
        return self::DELIVERY_KEY === $key;
    }

    public function process(\DateTimeInterface $lastOrderDate, ?\DateTimeInterface $result): \DateTimeInterface
    {
        $dateTime = new \DateTime($lastOrderDate->format('Y-m-d'));

        // Logic: Add 5 months for the next delivery
        $dateTime->add(new \DateInterval('P5M'));

        return $dateTime;
    }
}
```

{% endcode %}

```xml
<service id="B2bSellersExample\ProductSubscription\DeliveryInterval\Processor\CustomIntervalProcessor">
    <tag name="b2b_product_subscription.interval.processor"/>
</service>
```


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