Optimize commitData processing

Library:
- Subjects without duplicates where processed as a duplicate.
- First duplicate subject was altered and then unset.
- Conversion of hashes elements to an array was inefficient.

PHPUnit tests:
- First instance of duplicates is now kept instead of last.
  Updated Expected result for relevant tests.

src/GitChangeLog.php

@@ -361,12 +361,12 @@ public function fetchCommitData($force = false): array
             $commitData[$previousTag]['subjects'] =
                 explode(
                     "\n",
-                    shell_exec("git $gitPath log $tagRange $includeMergeCommits --pretty=format:%s --reverse")
+                    shell_exec("git $gitPath log $tagRange $includeMergeCommits --pretty=format:%s")
                 );
             $commitData[$previousTag]['hashes']   =
                 explode(
                     "\n",
-                    shell_exec("git $gitPath log $tagRange $includeMergeCommits --pretty=format:%h --reverse")
+                    shell_exec("git $gitPath log $tagRange $includeMergeCommits --pretty=format:%h")
                 );
             $previousTag                          = $tag;
         }
@@ -393,28 +393,20 @@ public function fetchCommitData($force = false): array
     private function processCommitData(): void
     {
         foreach ($this->commitData as $tag => &$data) {
-            // Remove duplicates per tag.
-            foreach ($data['subjects'] as $subjectKey => $subject) {
-                // Get indexes of current subject.
+            // Merge duplicate subjects per tag.
+            foreach ($data['subjects'] as $subjectKey => &$subject) {
+                // Convert hash element into an array.
+                $data['hashes'][$subjectKey] = [$data['hashes'][$subjectKey]];
+
+                // Get indexes of all other elements with the same subject as the current one.
                 $duplicates = array_keys($data['subjects'], $subject);
-                $hashes     = [];
+                array_shift($duplicates);
 
+                // Add hashes of duplicate subjects to the current subject and remove this duplicates.
                 // Subjects and hashes which belong to each other, have the same array key.
                 foreach ($duplicates as $key => $index) {
-                    // Collect hashes.
-                    if (!is_array($data['hashes'][$index])) {
-                        $hashes[] = $data['hashes'][$index];
-                    } else {
-                        $hashes = $data['hashes'][$index];
-                    }
-
-                    $data['hashes'][$index] = $hashes;
-
-                    // Remove all but last duplicate.
-                    end($duplicates);
-                    if ($key !== key($duplicates)) {
-                        unset($data['subjects'][$index], $data['hashes'][$index]);
-                    }
+                    $data['hashes'][$subjectKey][] = $data['hashes'][$index];
+                    unset($data['subjects'][$index], $data['hashes'][$index]);
                 }
 
                 // Remove subjects and hashes without specified labels.

tests/GitChangeLogTest.php

@@ -232,7 +232,7 @@ public function testSetFromTag()
 
     public function testBuildAscendingCommitOrder()
     {
-        $changeLog      = new GitChangeLog();
+        $changeLog = new GitChangeLog();
         $changeLog->setOptions('tagOrderDesc', false);
         $testValues     =
             [
@@ -266,7 +266,7 @@ public function testBuildAscendingCommitOrder()
 
     public function testBuildDescendingCommitOrder()
     {
-        $changeLog      = new GitChangeLog();
+        $changeLog = new GitChangeLog();
         $changeLog->setOptions('commitOrder', 'DESC');
         $testValues     =
             [
@@ -305,20 +305,26 @@ public function testProcessCommitData()
         $method->setAccessible(true);
 
         $changeLog = new GitChangeLog();
-        $changeLog->setLabels('C', 'D');
+        $changeLog->setLabels('C', 'D', 'F');
 
-        $value = ['A' => ['date' => 'B', 'subjects' => ['C', 'D', 'C', 'E'], 'hashes' => ['F', 'G', 'H', 'I']]];
-        $this->setPrivateProperty($changeLog, 'commitData', $value);
-        $value = [
+        $commitData = [
+            'A' => [
+                'date'     => 'B',
+                'subjects' => [0 => 'C', 1 => 'D', 2 => 'C', 3 => 'E', 4 => 'F'],
+                'hashes'   => [0 => 'G', 1 => 'H', 2 => 'I', 3 => 'J', 4 => 'K'],
+            ],
+        ];
+        $this->setPrivateProperty($changeLog, 'commitData', $commitData);
+        $commitData = [
             'A' => [
                 'date'     => 'B',
-                'subjects' => [1 => 'D', 2 => 'C'],
-                'hashes'   => [1 => ['G'], 2 => ['F', 'H']],
+                'subjects' => [0 => 'C', 1 => 'D', 4 => 'F'],
+                'hashes'   => [0 => ['G', 'I'], 1 => ['H'], 4 => ['K']],
             ],
         ];
         $method->invokeArgs($changeLog, []);
 
-        $this->assertEquals($value, $this->getPrivateProperty($changeLog, 'commitData'));
+        $this->assertEquals($commitData, $this->getPrivateProperty($changeLog, 'commitData'));
     }
 
     public function testAddLabel()