Support selection of the highest tax rate in the basket for shipping

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);
+});