Support selection of the highest tax rate in the basket for shipping (#…

…1937)

Currently the shipping tables add-on only supports returning the default
tax class/rate.

However countries can have different requirements for how tax should be
calculated on shipping depending on what is in the basket, for example
in the UK shipping should take the most expensive tax rate in the
basket.

This PR updates the add-on with a new config option
(`lunar.shipping-tables.shipping_rate_tax_calculation`) which currently
has two options: `default` for selecting the default rate, or `highest`
for selecting the highest rate in the basket.

---------

Co-authored-by: Author <actions@github.com>

packages/table-rate-shipping/config/shipping-tables.php

@@ -2,4 +2,11 @@
 
 return [
     'enabled' => env('LUNAR_SHIPPING_TABLES_ENABLED', true),
+
+    /*
+     * What method should we use for a shipping rate tax calculation?
+     * Options are 'default' for the system-wide default tax rate,
+     * or 'highest' to select the highest tax rate in the cart
+     */
+    'shipping_rate_tax_calculation' => 'default',
 ];

packages/table-rate-shipping/src/Models/ShippingRate.php

@@ -28,6 +28,8 @@ class ShippingRate extends BaseModel implements Contracts\ShippingRate, Purchasa
      */
     protected $guarded = [];
 
+    private ?TaxClass $resolvedTaxClass;
+
     protected static function booted()
     {
         self::deleting(function (self $shippingRate) {
@@ -73,7 +75,7 @@ public function getUnitQuantity(): int
      */
     public function getTaxClass(): TaxClass
     {
-        return TaxClass::getDefault();
+        return $this->resolvedTaxClass ?? TaxClass::getDefault();
     }
 
     public function getTaxReference(): ?string
@@ -139,6 +141,10 @@ public function getThumbnail(): ?string
      */
     public function getShippingOption(Cart $cart): ?ShippingOption
     {
+        if (config('lunar.shipping-tables.shipping_rate_tax_calculation') == 'highest') {
+            $this->resolvedTaxClass = $this->resolveHighestTaxRateInCart($cart);
+        }
+
         return $this->shippingMethod->driver()->resolve(
             new ShippingOptionRequest(
                 shippingRate: $this,
@@ -156,4 +162,23 @@ public function getTotalInventory(): int
     {
         return 1;
     }
+
+    private function resolveHighestTaxRateInCart(Cart $cart): ?TaxClass
+    {
+        $highestRate = false;
+        $highestTaxClass = null;
+
+        foreach ($cart->lines as $cartLine) {
+            if ($cartLine->purchasable->taxClass) {
+                foreach ($cartLine->purchasable->taxClass->taxRateAmounts as $amount) {
+                    if ($highestRate === false || $amount->percentage > $highestRate) {
+                        $highestRate = $amount->percentage;
+                        $highestTaxClass = $cartLine->purchasable->taxClass;
+                    }
+                }
+            }
+        }
+
+        return $highestTaxClass;
+    }
 }

tests/shipping/Unit/Resolvers/ShippingOptionResolverTest.php

@@ -5,7 +5,10 @@
 use Lunar\Models\CartAddress;
 use Lunar\Models\Country;
 use Lunar\Models\Currency;
+use Lunar\Models\Price;
+use Lunar\Models\ProductVariant;
 use Lunar\Models\TaxClass;
+use Lunar\Models\TaxRateAmount;
 use Lunar\Shipping\DataTransferObjects\ShippingOptionLookup;
 use Lunar\Shipping\Facades\Shipping;
 use Lunar\Shipping\Models\ShippingMethod;
@@ -94,3 +97,118 @@
 
     $this->assertcount(1, $options);
 });
+
+test('sets tax rate to the highest basket rate', function () {
+    config()->set('lunar.shipping-tables.shipping_rate_tax_calculation', 'highest');
+
+    $currency = Currency::factory()->create([
+        'default' => true,
+    ]);
+
+    $country = Country::factory()->create();
+
+    TaxClass::factory()->create([
+        'default' => true,
+        'name' => 'default',
+    ]);
+
+    $higherRate = TaxClass::factory()->create([
+        'default' => false,
+        'name' => 'higher',
+    ]);
+
+    $taxAmount = TaxRateAmount::factory()->create();
+    $taxAmount->percentage = 90;
+
+    $higherRate->taxRateAmounts()->save($taxAmount);
+
+    $customerGroup = \Lunar\Models\CustomerGroup::factory()->create([
+        'default' => true,
+    ]);
+
+    $shippingZone = ShippingZone::factory()->create([
+        'type' => 'countries',
+    ]);
+
+    $shippingZone->countries()->attach($country);
+
+    $shippingMethod = ShippingMethod::factory()->create([
+        'driver' => 'ship-by',
+        'data' => [
+            'minimum_spend' => [
+                "{$currency->code}" => 200,
+            ],
+        ],
+    ]);
+
+    $shippingMethod->customerGroups()->sync([
+        $customerGroup->id => ['enabled' => true, 'visible' => true, 'starts_at' => now(), 'ends_at' => null],
+    ]);
+
+    $shippingRate = \Lunar\Shipping\Models\ShippingRate::factory()
+        ->create([
+            'shipping_method_id' => $shippingMethod->id,
+            'shipping_zone_id' => $shippingZone->id,
+        ]);
+
+    $shippingRate->prices()->createMany([
+        [
+            'price' => 600,
+            'min_quantity' => 1,
+            'currency_id' => $currency->id,
+        ],
+        [
+            'price' => 500,
+            'min_quantity' => 700,
+            'currency_id' => $currency->id,
+        ],
+        [
+            'price' => 0,
+            'min_quantity' => 800,
+            'currency_id' => $currency->id,
+        ],
+    ]);
+
+    $cart = $this->createCart($currency, 500);
+
+    $purchasable = ProductVariant::factory()->create();
+    $purchasable->stock = 50;
+    $purchasable->tax_class_id = $higherRate->id;
+    $purchasable->save();
+
+    Price::factory()->create([
+        'price' => 300,
+        'min_quantity' => 1,
+        'currency_id' => $currency->id,
+        'priceable_type' => $purchasable->getMorphClass(),
+        'priceable_id' => $purchasable->id,
+    ]);
+
+    $cart->lines()->create([
+        'purchasable_type' => $purchasable->getMorphClass(),
+        'purchasable_id' => $purchasable->id,
+        'quantity' => 1,
+    ]);
+
+    $cart->shippingAddress()->create(
+        CartAddress::factory()->make([
+            'country_id' => $country->id,
+            'state' => null,
+        ])->toArray()
+    );
+
+    $shippingRates = Shipping::shippingRates(
+        $cart->refresh()->calculate()
+    )->get();
+
+    $options = Shipping::shippingOptions()->cart(
+        $cart->refresh()->calculate()
+    )->get(
+        new ShippingOptionLookup(
+            shippingRates: $shippingRates
+        )
+    );
+
+    $this->assertcount(1, $options);
+    $this->assertSame($options->first()->option->taxClass->id, $higherRate->id);
+});