Extending Discounts

A custom discount type is a class registered with the discount manager, invoked against a cart during the discount stage of cart calculation.

The discount type contract

Every discount type implements Lunar\Core\Contracts\DiscountType:

namespace Lunar\Core\Contracts;

use Lunar\Core\Models\Cart;

interface DiscountType
{
    /**
     * Return the name of the discount type.
     */
    public function getName(): string;

    /**
     * Execute and apply the discount if conditions are met.
     */
    public function apply(Cart $cart): Cart;
}

Extend Lunar\Core\DiscountTypes\AbstractDiscountType rather than implementing the interface directly. It supplies the Discount model the type is running for ($this->discount, set via with()), plus helpers a discount type typically needs:

markAsUsed(Cart $cart) — increments the discount’s use count and records the cart’s user against it.
getEligibleLines(Cart $cart) — the cart lines the discount can apply to; defaults to every line.
checkDiscountConditions(Cart $cart) — validates the discount’s customer restriction, coupon match, minimum spend, and use limits.
addDiscountBreakdown(Cart $cart, DiscountBreakdown $breakdown) — records the discount against the cart’s breakdown, which is what makes it show up as applied.

<?php

namespace App\DiscountTypes;

use Lunar\Core\DiscountTypes\AbstractDiscountType;
use Lunar\Core\Models\Cart;

class MyCustomDiscountType extends AbstractDiscountType
{
    public function getName(): string
    {
        return 'Custom Discount Type';
    }

    public function apply(Cart $cart): Cart
    {
        if (! $this->checkDiscountConditions($cart)) {
            return $cart;
        }

        // Apply the discount to $cart, then:
        $this->addDiscountBreakdown($cart, $breakdown);
        $this->markAsUsed($cart);

        return $cart;
    }
}

Lunar’s own built-in types follow the same shape: Lunar\Core\DiscountTypes\PercentageOff, Lunar\Core\DiscountTypes\FixedAmountOff, and Lunar\Core\DiscountTypes\BuyXGetY. PercentageOff and FixedAmountOff also use Lunar\Core\DiscountTypes\Concerns\TargetsCartLines, a trait that narrows getEligibleLines() to the discount’s collection, brand, product, or variant limitations — reach for it when a discount type should target specific lines rather than the whole cart.

Registering a discount type

use Lunar\Core\Facades\Discounts;

public function boot(): void
{
    Discounts::addType(\App\DiscountTypes\MyCustomDiscountType::class);
}

Discounts resolves Lunar\Core\Contracts\DiscountManager, implemented by Lunar\Core\Managers\DiscountManager. There is no config-based registration; addType() is the only seam.

A discount record stores its type’s class name directly in its own type column — addType() registers the class with the manager (which drives the admin type picker and validation), but at apply time each Discount instantiates its own stored type via Discount::getType().

Applying discounts to a cart

Discounts run as part of the cart calculation pipeline (see Extending Carts), in the ApplyDiscounts step:

class ApplyDiscounts
{
    public function handle(Cart $cart, Closure $next): mixed
    {
        $cart->discounts = collect([]);
        $cart->discountBreakdown = collect([]);

        Discounts::apply($cart);

        return $next($cart);
    }
}

DiscountManager::apply() fetches every eligible Discount, ordered by priority descending (ties broken by id), and calls each one’s type’s apply($cart) in turn. A discount’s stop flag, when true, halts the loop as soon as that discount applies — lower-priority discounts after it are skipped. Both priority and stop are plain columns on the Discount model, set through its admin form; a discount type does not need to implement anything to participate in ordering or stopping, as long as apply() calls addDiscountBreakdown() when it actually applies.

Adding an admin form

A discount type with no registered form still works — the storefront applies it — but it has no dedicated fields in an admin panel. To add one:

Filament admin: implement Lunar\Admin\Base\LunarPanelDiscountInterface, which requires lunarPanelSchema(), lunarPanelOnFill(), lunarPanelOnSave(), and lunarPanelRelationManagers().
Inertia panel: see Discount Type Forms for the panel’s own DiscountTypeForm contract.

A type can implement both to serve both admins from one class; neither is required by the other.

​The discount type contract

​Registering a discount type

​Applying discounts to a cart

​Adding an admin form

The discount type contract

Registering a discount type

Applying discounts to a cart

Adding an admin form