diff --git a/.gitignore b/.gitignore
index 9c01165..7151afe 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,5 +4,4 @@
 log.txt
 result.csv
 .run
-*.lock
 .php-cs-fixer.cache
diff --git a/README.md b/README.md
index c1dace2..83f66c8 100644
--- a/README.md
+++ b/README.md
@@ -54,14 +54,8 @@ _numbers are 3 and 0 are wrong, is not allowed_ <br/>
 ## Task 
 You need to refactor code and write it on proper way. Just do your best: update/delete/add code as you wish.
 
-After finishing - please push your code in your github/bitbucket account, and send me link back.
-
 ### Requirements
 
 * After refactoring code shoud work
 * Code should work on PHP8.0+
 * As file source example please use test.csv
-
-### Result
-Please put result of your work in your Github or Bitbucket account, and send link back.
-
diff --git a/composer.lock b/composer.lock
new file mode 100644
index 0000000..d26d95e
--- /dev/null
+++ b/composer.lock
@@ -0,0 +1,20 @@
+{
+    "_readme": [
+        "This file locks the dependencies of your project to a known state",
+        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
+        "This file is @generated automatically"
+    ],
+    "content-hash": "63e7cd6af94fff1be77b03d112d0b91c",
+    "packages": [],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": [],
+    "prefer-stable": false,
+    "prefer-lowest": false,
+    "platform": {
+        "php": ">=8.1"
+    },
+    "platform-dev": [],
+    "plugin-api-version": "2.3.0"
+}
diff --git a/src/Csv/CsvWriter.php b/src/Csv/CsvWriter.php
index aaef145..8f9089f 100644
--- a/src/Csv/CsvWriter.php
+++ b/src/Csv/CsvWriter.php
@@ -6,23 +6,37 @@ namespace App\Csv;
 
 use RuntimeException;
 
-class CsvWriter
+final class CsvWriter
 {
     private string $separator = ';';
 
+    /**
+     * @var false|resource
+     */
+    private $fileHandle;
+
     public function __construct(private readonly string $filePath)
     {
         file_put_contents($this->filePath, '');
     }
 
+    /**
+     * @param array<int,mixed> $data
+     */
     public function addLine(array $data): void
     {
-        $handle = fopen($this->filePath, 'ab');
-        if (!$handle) {
-            throw new RuntimeException('Could not open file.');
+        if (!$this->fileHandle) {
+            $this->fileHandle = fopen($this->filePath, 'ab');
+            if (!$this->fileHandle) {
+                throw new RuntimeException('Could not open file.');
+            }
         }
 
-        fputcsv($handle, $data, $this->separator);
-        fclose($handle);
+        fputcsv($this->fileHandle, $data, $this->separator);
+    }
+
+    public function __destruct()
+    {
+        fclose($this->fileHandle);
     }
 }
diff --git a/src/CsvCalculationService.php b/src/CsvCalculationService.php
index 60bc4f5..df233c2 100644
--- a/src/CsvCalculationService.php
+++ b/src/CsvCalculationService.php
@@ -10,7 +10,7 @@ use App\Logger\LoggerInterface;
 use App\Operations\Exceptions\InvalidResultException;
 use App\Operations\MathOperationInterface;
 
-class CsvCalculationService
+private class CsvCalculationService
 {
     public function __construct(
         private readonly CsvReader $csvReader,
diff --git a/src/MathOperationFactory.php b/src/MathOperationFactory.php
index cfb241e..20333ef 100644
--- a/src/MathOperationFactory.php
+++ b/src/MathOperationFactory.php
@@ -12,7 +12,7 @@ use App\Operations\Subtract;
 use App\Operations\Multiply;
 use App\Options\CliOption;
 
-class MathOperationFactory
+final class MathOperationFactory
 {
     public static function getOperationFromCliOption(CliOption $cliOption): MathOperationInterface
     {