Reverse internal ordering of ItemList so that it can use O(1) array_p…

…op rather than O(n) array_shift

src/ItemList.php

@@ -12,9 +12,10 @@
 use Countable;
 use IteratorAggregate;
 use Traversable;
-use function array_shift;
+use function array_pop;
+use function array_reverse;
 use function count;
-use function reset;
+use function end;
 use function usort;
 
 /**
@@ -87,7 +88,7 @@ public function extract(): Item
  $this->isSorted = true;
  }
 
- return array_shift($this->list);
+ return array_pop($this->list);
  }
 
  /**
@@ -103,7 +104,7 @@ public function top(): Item
  }
  $temp = $this->list;
 
- return reset($temp);
+ return end($temp);
  }
 
  /**
@@ -116,7 +117,7 @@ public function getIterator(): Traversable
  $this->isSorted = true;
  }
 
- return new ArrayIterator($this->list);
+ return new ArrayIterator(array_reverse($this->list));
  }
 
  /**
@@ -139,14 +140,15 @@ private function compare(Item $itemA, Item $itemB): int
  {
  $itemAVolume = $itemA->getWidth() * $itemA->getLength() * $itemA->getDepth();
  $itemBVolume = $itemB->getWidth() * $itemB->getLength() * $itemB->getDepth();
- $volumeDecider = $itemBVolume <=> $itemAVolume;
- $weightDecider = $itemB->getWeight() - $itemA->getWeight();
+ $volumeDecider = $itemAVolume <=> $itemBVolume;
+ $weightDecider = $itemA->getWeight() - $itemB->getWeight();
  if ($volumeDecider !== 0) {
  return $volumeDecider;
- } elseif ($weightDecider !== 0) {
+ }
+ if ($weightDecider !== 0) {
  return $weightDecider;
- } else {
- return $itemA->getDescription() <=> $itemB->getDescription();
  }
+
+ return $itemB->getDescription() <=> $itemA->getDescription();
  }
 }