Cover situation when all of discount isnt actually able to be used (#…

…1272)

packages/core/src/DiscountTypes/AmountOff.php

@@ -107,34 +107,40 @@ private function applyFixedValue(array $values, Cart $cart): Cart
         // enough left to apply the remaining too.
         if ($remaining) {
             // prioritise sharing the remaining over eligible lines
-            $line = $lines->first(function ($line) use ($remaining) {
-                return $line->subTotalDiscounted->value - $remaining > 0;
-            });
-
-            if ($line) {
-                $newDiscountTotal = $line->discountTotal->value + $remaining;
-
-                $line->discountTotal = new Price(
-                    $newDiscountTotal,
-                    $cart->currency,
-                    1
-                );
-
-                $line->subTotalDiscounted = new Price(
-                    $line->subTotal->value - $newDiscountTotal,
-                    $cart->currency,
-                    1
-                );
-
-                if (! $affectedLines->first(function ($breakdownLine) use ($line) {
-                    return $breakdownLine->line == $line;
-                })) {
-                    $affectedLines->push(new DiscountBreakdownLine(
-                        line: $line,
-                        quantity: $line->quantity
-                    ));
-                }
-            }
+            $lines->filter(function ($line) {
+                return $line->subTotalDiscounted->value > 0;
+            })
+                ->each(function($line) use ($affectedLines, $cart, &$remaining) {
+                    if ($remaining <= 0) {
+                        return;
+                    }
+
+                    $amountAvailable = min($line->subTotalDiscounted->value, $remaining);
+                    $remaining -= $amountAvailable;
+
+                    $newDiscountTotal = $line->discountTotal->value + $amountAvailable;
+
+                    $line->discountTotal = new Price(
+                        $newDiscountTotal,
+                        $cart->currency,
+                        1
+                    );
+
+                    $line->subTotalDiscounted = new Price(
+                        $line->subTotal->value - $newDiscountTotal,
+                        $cart->currency,
+                        1
+                    );
+
+                    if (! $affectedLines->first(function ($breakdownLine) use ($line) {
+                        return $breakdownLine->line == $line;
+                    })) {
+                        $affectedLines->push(new DiscountBreakdownLine(
+                            line: $line,
+                            quantity: $line->quantity
+                        ));
+                    }
+                });
         }
 
         if (! $cart->discounts) {
@@ -146,7 +152,7 @@ private function applyFixedValue(array $values, Cart $cart): Cart
         $this->addDiscountBreakdown($cart, new DiscountBreakdown(
             discount: $this->discount,
             lines: $affectedLines,
-            price: new Price($value, $cart->currency, 1)
+            price: new Price($value - $remaining, $cart->currency, 1)
         ));
 
         return $cart;

packages/core/tests/Unit/DiscountTypes/AmountOffTest.php

@@ -1356,9 +1356,9 @@ public function fixed_amount_discount_distributes_across_cart_lines_with_differe
         $this->assertGreaterThanOrEqual(0, $fourthLine->subTotalDiscounted->value);
         $this->assertGreaterThanOrEqual(0, $lastLine->subTotalDiscounted->value);
 
-        $this->assertEquals(149, $firstLine->discountTotal->value);
-        $this->assertEquals(198, $secondLine->discountTotal->value);
-        $this->assertEquals(399, $thirdLine->discountTotal->value);
+        $this->assertEquals(150, $firstLine->discountTotal->value);
+        $this->assertEquals(199, $secondLine->discountTotal->value);
+        $this->assertEquals(397, $thirdLine->discountTotal->value);
         $this->assertEquals(397, $fourthLine->discountTotal->value);
         $this->assertEquals(357, $lastLine->discountTotal->value);
         $this->assertEquals(1500, $cart->discountTotal->value);