Raise exception when doing first/last operations on an empty Version …

…collection

src/Exception/CollectionIsEmpty.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Version\Exception;
+
+use OutOfBoundsException;
+
+final class CollectionIsEmpty extends OutOfBoundsException implements VersionException
+{
+    public static function cannotGetFirst(): self
+    {
+        return new self('Cannot get the first Version from an empty collection');
+    }
+
+    public static function cannotGetLast(): self
+    {
+        return new self('Cannot get the last Version from an empty collection');
+    }
+}

src/VersionCollection.php

@@ -9,6 +9,7 @@
 use ArrayIterator;
 use Traversable;
 use Version\Comparison\Constraint\Constraint;
+use Version\Exception\CollectionIsEmpty;
 
 class VersionCollection implements Countable, IteratorAggregate
 {
@@ -29,14 +30,25 @@ public function isEmpty(): bool
         return empty($this->versions);
     }
 
-    public function first(): ?Version
+    public function first(): Version
     {
-        return $this->versions[0] ?? null;
+        if (empty($this->versions)) {
+            throw CollectionIsEmpty::cannotGetFirst();
+        }
+
+        return reset($this->versions);
     }
 
-    public function last(): ?Version
+    public function last(): Version
     {
-        return $this->versions[count($this->versions) - 1] ?? null;
+        if (empty($this->versions)) {
+            throw CollectionIsEmpty::cannotGetLast();
+        }
+
+        $version = end($this->versions);
+        reset($this->versions);
+
+        return $version;
     }
 
     public function getIterator(): Traversable

tests/VersionCollectionTest.php

@@ -5,6 +5,7 @@
 namespace Version\Tests;
 
 use PHPUnit\Framework\TestCase;
+use Version\Exception\CollectionIsEmpty;
 use Version\Tests\TestAsset\VersionIsIdentical;
 use Version\Tests\TestAsset\VersionCollectionIsIdentical;
 use Version\VersionCollection;
@@ -72,6 +73,22 @@ public function it_gets_first_version(): void
         $this->assertThat($version, new VersionIsIdentical(1, 0, 0));
     }
 
+    /**
+     * @test
+     */
+    public function it_raises_exception_when_getting_first_item_of_empty_collection(): void
+    {
+        $versions = new VersionCollection();
+
+        try {
+            $versions->first();
+
+            $this->fail('Exception should have been raised');
+        } catch (CollectionIsEmpty $ex) {
+            $this->assertSame('Cannot get the first Version from an empty collection', $ex->getMessage());
+        }
+    }
+
     /**
      * @test
      */
@@ -92,12 +109,17 @@ public function it_gets_last_version(): void
     /**
      * @test
      */
-    public function it_doesnt_return_first_last_versions_if_empty(): void
+    public function it_raises_exception_when_getting_last_item_of_empty_collection(): void
     {
         $versions = new VersionCollection();
 
-        $this->assertNull($versions->first());
-        $this->assertNull($versions->last());
+        try {
+            $versions->last();
+
+            $this->fail('Exception should have been raised');
+        } catch (CollectionIsEmpty $ex) {
+            $this->assertSame('Cannot get the last Version from an empty collection', $ex->getMessage());
+        }
     }
 
     /**