diff --git a/.github/workflows/pr-ci.yml b/.github/workflows/pr-ci.yml
index 61f9c70..6563da6 100644
--- a/.github/workflows/pr-ci.yml
+++ b/.github/workflows/pr-ci.yml
@@ -27,9 +27,12 @@ jobs:
       # 4️⃣ PSR-12 Code Style Check
       - name: Check PSR-12 Coding Standards
         run: |
-          composer global require "squizlabs/php_codesniffer=*"
-          phpcs --standard=PSR12 --extensions=php -n . bin/audit-class-generator
+          composer global require squizlabs/php_codesniffer
+          phpcs --standard=PSR12 --extensions=php -n \
+            bin/audit-class-generator \
+            src \
+            tests
 
       # 5️⃣ Run PHPUnit Tests
       - name: Run PHPUnit Tests
-        run: vendor/bin/phpunit --colors=always Tests/
+        run: vendor/bin/phpunit --colors=always tests/
diff --git a/bin/audit-class-generator b/bin/audit-class-generator
index a80859e..3038b58 100755
--- a/bin/audit-class-generator
+++ b/bin/audit-class-generator
@@ -1,8 +1,13 @@
 #!/usr/bin/env php
-<?php declare(strict_types=1);
+<?php
 
-use PatrickMaynard\AuditClassGenerator\Applier;
-use PatrickMaynard\AuditClassGenerator\Config;
+declare(strict_types=1);
+
+use PatrickMaynard\AuditClassGenerator\Application\BusinessLogic\Applier;
+use PatrickMaynard\AuditClassGenerator\Application\Config\Config;
+use PatrickMaynard\AuditClassGenerator\Infrastructure\FileSystem\DirectoryScanner;
+use PatrickMaynard\AuditClassGenerator\Infrastructure\FileSystem\ExtensionFilter;
+use PatrickMaynard\AuditClassGenerator\Infrastructure\FileSystem\FileIO;
 
 include $_composer_autoload_path ?? __DIR__ . '/../vendor/autoload.php';
 
@@ -34,53 +39,19 @@ echo PHP_EOL;
 
 $applier = new Applier();
 
-$files = filterAllFilesForTwigExtension($config);
+$scanner = new DirectoryScanner();
+$filter = new ExtensionFilter($config->getExtension());
+$fileIO = new FileIO();
 
-foreach ($files as $index => $file) {
-    $contents = file_get_contents($file);
+foreach ($scanner->scan($config->getDirectory()) as $file) {
+    if (!$filter->matches($file)) {
+        continue;
+    }
 
-    file_put_contents($file, $applier->applyAllAuditTags($contents));
+    $content = $fileIO->read($file);
+    $processed = $applier->applyAllAuditTags($content);
+    $fileIO->write($file, $processed);
 }
 
 echo "Done!";
 echo PHP_EOL;
-
-//TODO: Allow blade as well. Maybe solved with configuration
-function filterAllFilesForTwigExtension(Config $config): array
-{
-    $directoryToParse = getcwd() . DIRECTORY_SEPARATOR . $config->getDirectory();
-
-    echo PHP_EOL . 'We will be looking recursively in ' . $directoryToParse . ' for Twig files .. ' . PHP_EOL;
-
-    $files = getDirContents($directoryToParse);
-    $output = [];
-
-    foreach ($files as $file) {
-        if (str_ends_with($file, $config->getExtension())) {
-            $output[] = $file;
-        }
-    }
-
-    return $output;
-}
-
-function getDirContents($dir): array
-{
-    $results = [];
-    $files = scandir($dir);
-
-    foreach ($files as $key => $value) {
-        if (!is_dir($dir . DIRECTORY_SEPARATOR . $value)) {
-            $results[] = $dir . DIRECTORY_SEPARATOR . $value;
-        } elseif (
-            is_dir($dir . DIRECTORY_SEPARATOR . $value)
-            && !str_contains($value, '..')
-            && $value !== '.'
-        ) {
-            $results[] = $value;
-            $results = array_merge($results, getDirContents($dir . DIRECTORY_SEPARATOR . $value));
-        }
-    }
-
-    return $results;
-}
diff --git a/composer.json b/composer.json
index 7554e5e..89d5963 100644
--- a/composer.json
+++ b/composer.json
@@ -20,12 +20,17 @@
         "twig/twig": "*"
     },
     "require-dev": {
-        "symfony/phpunit-bridge": "^4.4.9|^5.0.9|^6.0"
+        "phpunit/phpunit": "^9.6",
+        "mikey179/vfsstream": "^1.6"
     },
     "autoload": {
-        "psr-4" : { "PatrickMaynard\\AuditClassGenerator\\" : "" },
-        "exclude-from-classmap": [
-            "/Tests/"
-        ]
+        "psr-4" : {
+            "PatrickMaynard\\AuditClassGenerator\\" : "src/"
+        }
+    },
+    "autoload-dev": {
+        "psr-4" : {
+            "PatrickMaynard\\AuditClassGenerator\\Tests\\" : "tests/"
+        }
     }
 }
diff --git a/Applier.php b/src/Application/BusinessLogic/Applier.php
similarity index 93%
rename from Applier.php
rename to src/Application/BusinessLogic/Applier.php
index 5699645..7b416ea 100644
--- a/Applier.php
+++ b/src/Application/BusinessLogic/Applier.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace PatrickMaynard\AuditClassGenerator;
+namespace PatrickMaynard\AuditClassGenerator\Application\BusinessLogic;
 
 class Applier
 {
diff --git a/Config.php b/src/Application/Config/Config.php
similarity index 82%
rename from Config.php
rename to src/Application/Config/Config.php
index a351184..494eab2 100644
--- a/Config.php
+++ b/src/Application/Config/Config.php
@@ -1,9 +1,11 @@
 <?php
-declare(strict_types = 1);
 
-namespace PatrickMaynard\AuditClassGenerator;
+declare(strict_types=1);
 
-class Config {
+namespace PatrickMaynard\AuditClassGenerator\Application\Config;
+
+class Config
+{
     private string $directory;
     private string $extension;
     private bool $verbose;
@@ -22,7 +24,7 @@ public static function create(array $options): self
     {
         return new self(
             $options['directory'] ?? $options['d'] ?? 'templates',
-            $options['extension'] ?? $options['e'] ?? '.html.twig',
+            $options['extension'] ?? $options['e'] ?? 'html.twig',
             isset($options['v']) || isset($options['verbose'])
         );
     }
diff --git a/src/Infrastructure/Exception/EmptyFileException.php b/src/Infrastructure/Exception/EmptyFileException.php
new file mode 100644
index 0000000..075df9f
--- /dev/null
+++ b/src/Infrastructure/Exception/EmptyFileException.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PatrickMaynard\AuditClassGenerator\Infrastructure\Exception;
+
+class EmptyFileException extends \RuntimeException
+{
+    public function __construct(string $path)
+    {
+        parent::__construct(
+            sprintf('File is empty: %s', $path)
+        );
+    }
+}
diff --git a/src/Infrastructure/Exception/FileDoesNotExistException.php b/src/Infrastructure/Exception/FileDoesNotExistException.php
new file mode 100644
index 0000000..24aa5c4
--- /dev/null
+++ b/src/Infrastructure/Exception/FileDoesNotExistException.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PatrickMaynard\AuditClassGenerator\Infrastructure\Exception;
+
+class FileDoesNotExistException extends \RuntimeException
+{
+    public function __construct(string $path)
+    {
+        parent::__construct(
+            sprintf('File does not exist: %s', $path)
+        );
+    }
+}
diff --git a/src/Infrastructure/Exception/FileNotWritableException.php b/src/Infrastructure/Exception/FileNotWritableException.php
new file mode 100644
index 0000000..3c3cc09
--- /dev/null
+++ b/src/Infrastructure/Exception/FileNotWritableException.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PatrickMaynard\AuditClassGenerator\Infrastructure\Exception;
+
+class FileNotWritableException extends \RuntimeException
+{
+    public function __construct(string $path)
+    {
+        parent::__construct(
+            sprintf('File not writable: %s', $path)
+        );
+    }
+}
diff --git a/src/Infrastructure/FileSystem/DirectoryScanner.php b/src/Infrastructure/FileSystem/DirectoryScanner.php
new file mode 100644
index 0000000..4a44932
--- /dev/null
+++ b/src/Infrastructure/FileSystem/DirectoryScanner.php
@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PatrickMaynard\AuditClassGenerator\Infrastructure\FileSystem;
+
+class DirectoryScanner
+{
+    public function scan(string $path): iterable
+    {
+        $iterator = new \RecursiveIteratorIterator(
+            new \RecursiveDirectoryIterator(
+                $path,
+                \FilesystemIterator::SKIP_DOTS
+            )
+        );
+
+        foreach ($iterator as $file) {
+            if ($file->isFile()) {
+                yield $file->getPathname();
+            }
+        }
+    }
+}
diff --git a/src/Infrastructure/FileSystem/ExtensionFilter.php b/src/Infrastructure/FileSystem/ExtensionFilter.php
new file mode 100644
index 0000000..f7f41ac
--- /dev/null
+++ b/src/Infrastructure/FileSystem/ExtensionFilter.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PatrickMaynard\AuditClassGenerator\Infrastructure\FileSystem;
+
+class ExtensionFilter
+{
+    public function __construct(private string $extension)
+    {
+    }
+
+    public function matches(string $filePath): bool
+    {
+        return pathinfo($filePath, PATHINFO_EXTENSION) === $this->extension;
+    }
+}
diff --git a/src/Infrastructure/FileSystem/FileIO.php b/src/Infrastructure/FileSystem/FileIO.php
new file mode 100644
index 0000000..d502b6e
--- /dev/null
+++ b/src/Infrastructure/FileSystem/FileIO.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PatrickMaynard\AuditClassGenerator\Infrastructure\FileSystem;
+
+use PatrickMaynard\AuditClassGenerator\Infrastructure\Exception\EmptyFileException;
+use PatrickMaynard\AuditClassGenerator\Infrastructure\Exception\FileDoesNotExistException;
+use PatrickMaynard\AuditClassGenerator\Infrastructure\Exception\FileNotWritableException;
+
+class FileIO
+{
+    public function read(string $path): string
+    {
+        if (!file_exists($path)) {
+            throw new FileDoesNotExistException("File does not exist: {$path}");
+        }
+
+        $contents = file_get_contents($path);
+
+        $hasBom = str_starts_with($contents, "\xEF\xBB\xBF");
+
+        if ($contents === '' || ($hasBom && strlen($contents) === 3)) {
+            throw new EmptyFileException($path);
+        }
+
+        return $contents;
+    }
+
+    public function write(string $path, string $content): void
+    {
+        if (!file_exists($path)) {
+            throw new FileDoesNotExistException($path);
+        }
+
+        if (!is_writable($path)) {
+            throw new FileNotWritableException($path);
+        }
+
+        file_put_contents($path, $content);
+    }
+}
diff --git a/Tests/ApplierTest.php b/tests/Application/BusinessLogic/ApplierTest.php
similarity index 89%
rename from Tests/ApplierTest.php
rename to tests/Application/BusinessLogic/ApplierTest.php
index 660045f..585d8c6 100644
--- a/Tests/ApplierTest.php
+++ b/tests/Application/BusinessLogic/ApplierTest.php
@@ -1,8 +1,8 @@
 <?php
 
-namespace PatrickMaynard\AuditClassGenerator\Tests;
+namespace PatrickMaynard\AuditClassGenerator\Tests\Application\BusinessLogic;
 
-use PatrickMaynard\AuditClassGenerator\Applier;
+use PatrickMaynard\AuditClassGenerator\Application\BusinessLogic\Applier;
 use PHPUnit\Framework\TestCase;
 
 class ApplierTest extends TestCase
diff --git a/Tests/InstantiationTest.php b/tests/Application/Config/InstantiationTest.php
similarity index 56%
rename from Tests/InstantiationTest.php
rename to tests/Application/Config/InstantiationTest.php
index 6dc7d79..219a44c 100644
--- a/Tests/InstantiationTest.php
+++ b/tests/Application/Config/InstantiationTest.php
@@ -1,15 +1,15 @@
 <?php
 
-namespace PatrickMaynard\AuditClassGenerator\Tests;
+namespace PatrickMaynard\AuditClassGenerator\Tests\Application\Config;
 
-use PatrickMaynard\AuditClassGenerator\Applier;
+use PatrickMaynard\AuditClassGenerator\Application\BusinessLogic\Applier;
 use PHPUnit\Framework\TestCase;
 
 class InstantiationTest extends TestCase
 {
     public function testInstantiation(): void
     {
-        $applier = new Applier;
+        $applier = new Applier();
 
         //If there were no excpetions, we're good for now.
         self::assertTrue(true);
diff --git a/tests/Infrastructure/FileSystem/FileIOTest.php b/tests/Infrastructure/FileSystem/FileIOTest.php
new file mode 100644
index 0000000..50f18a8
--- /dev/null
+++ b/tests/Infrastructure/FileSystem/FileIOTest.php
@@ -0,0 +1,113 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PatrickMaynard\AuditClassGenerator\Tests\Infrastructure\FileSystem;
+
+use org\bovigo\vfs\vfsStream;
+use org\bovigo\vfs\vfsStreamDirectory;
+use PatrickMaynard\AuditClassGenerator\Infrastructure\Exception\EmptyFileException;
+use PatrickMaynard\AuditClassGenerator\Infrastructure\Exception\FileDoesNotExistException;
+use PatrickMaynard\AuditClassGenerator\Infrastructure\Exception\FileNotWritableException;
+use PatrickMaynard\AuditClassGenerator\Infrastructure\FileSystem\FileIO;
+use PHPUnit\Framework\TestCase;
+
+class FileIOTest extends TestCase
+{
+    private vfsStreamDirectory $root;
+
+    public function testReadFileDoesNotExist(): void
+    {
+        $path = vfsStream::url('root/nonexistentfile.txt');
+
+        $fileIO = new FileIO();
+
+        $this->expectException(FileDoesNotExistException::class);
+        $this->expectExceptionMessage('File does not exist: ' . $path);
+
+        $fileIO->read($path);
+    }
+
+    public function testReadFileIsEmpty(): void
+    {
+        $path = vfsStream::url('root/emptyfile.txt');
+
+        vfsStream::newFile('emptyfile.txt')->at($this->root); // Leere Datei erstellen
+
+        $fileIO = new FileIO();
+
+        $this->expectException(EmptyFileException::class);
+        $this->expectExceptionMessage('File is empty: ' . $path);
+
+        $fileIO->read($path);
+    }
+
+    public function testReadFileWithBomIsEmpty(): void
+    {
+        vfsStream::newFile('emptyfile.txt')
+            ->withContent("\xEF\xBB\xBF")
+            ->at($this->root); // Leere Datei mit BOM erstellen
+
+        $fileIO = new FileIO();
+        $this->expectException(\RuntimeException::class);
+        $fileIO->read(vfsStream::url('root/emptyfile.txt'));
+    }
+
+    public function testReadFileContainsTwigContent(): void
+    {
+        $content = 'Hello, {{ name }}!';
+        vfsStream::newFile('twigfile.txt')->withContent($content)->at($this->root);
+
+        $fileIO = new FileIO();
+        $result = $fileIO->read(vfsStream::url('root/twigfile.txt'));
+
+        $this->assertEquals($content, $result);
+    }
+
+    public function testWriteFileDoesNotExist(): void
+    {
+        $path = vfsStream::url('root/nonexistingdir/newfile.txt');
+
+        $fileIO = new FileIO();
+
+        $this->expectException(FileDoesNotExistException::class);
+        $this->expectExceptionMessage('File does not exist: ' . $path);
+
+        $fileIO->write($path, 'Test content');
+    }
+
+    public function testWriteFileExistsAndIsOverwritten(): void
+    {
+        $path = vfsStream::url('root/existingfile.txt');
+
+        vfsStream::newFile('existingfile.txt')->withContent('Old content')->at($this->root);
+
+        $fileIO = new FileIO();
+        $fileIO->write($path, 'New content');
+
+        $content = file_get_contents($path);
+        $this->assertEquals('New content', $content);
+    }
+
+    public function testWriteFileWithoutWritePermissions(): void
+    {
+        $path = vfsStream::url('root/readonlyfile.txt');
+
+        vfsStream::newFile('readonlyfile.txt')
+            ->chmod(0444)
+            ->at($this->root);
+
+        $fileIO = new FileIO();
+
+        $this->expectException(FileNotWritableException::class);
+        $this->expectExceptionMessage('File not writable: ' . $path);
+
+        $fileIO->write($path, 'Test content');
+    }
+
+    protected function setUp(): void
+    {
+        // Erstelle ein virtuelles Dateisystem (vfsStream)
+        $this->root = vfsStream::setup('root'); // Wurzelverzeichnis erstellen
+    }
+}