Refactor writers for better DI (#427)

This commit is a big refactor that improves the code organization.
It focuses on how dependencies are injected into the different classes. This is now done via some factories.

Also, the code is now built around entities (data model that only exposes getters and setters), managers (used to manage an entity) and helpers (used by the managers to perform some specific tasks).

The refactoring is not fully complete, as some dependencies are still hidden...

src/Spout/Common/Helper/FileSystemHelper.php

@@ -11,7 +11,7 @@ use Box\Spout\Common\Exception\IOException;
  *
  * @package Box\Spout\Common\Helper
  */
-class FileSystemHelper
+class FileSystemHelper implements FileSystemHelperInterface
 {
     /** @var string Real path of the base folder where all the I/O can occur */
     protected $baseFolderRealPath;

src/Spout/Common/Helper/FileSystemHelperInterface.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace Box\Spout\Common\Helper;
+
+/**
+ * Class FileSystemHelperInterface
+ * This interface describes helper functions to help with the file system operations
+ * like files/folders creation & deletion
+ *
+ * @package Box\Spout\Common\Helper
+ */
+interface FileSystemHelperInterface
+{
+    /**
+     * Creates an empty folder with the given name under the given parent folder.
+     *
+     * @param string $parentFolderPath The parent folder path under which the folder is going to be created
+     * @param string $folderName The name of the folder to create
+     * @return string Path of the created folder
+     * @throws \Box\Spout\Common\Exception\IOException If unable to create the folder or if the folder path is not inside of the base folder
+     */
+    public function createFolder($parentFolderPath, $folderName);
+
+    /**
+     * Creates a file with the given name and content in the given folder.
+     * The parent folder must exist.
+     *
+     * @param string $parentFolderPath The parent folder path where the file is going to be created
+     * @param string $fileName The name of the file to create
+     * @param string $fileContents The contents of the file to create
+     * @return string Path of the created file
+     * @throws \Box\Spout\Common\Exception\IOException If unable to create the file or if the file path is not inside of the base folder
+     */
+    public function createFileWithContents($parentFolderPath, $fileName, $fileContents);
+
+    /**
+     * Delete the file at the given path
+     *
+     * @param string $filePath Path of the file to delete
+     * @return void
+     * @throws \Box\Spout\Common\Exception\IOException If the file path is not inside of the base folder
+     */
+    public function deleteFile($filePath);
+
+    /**
+     * Delete the folder at the given path as well as all its contents
+     *
+     * @param string $folderPath Path of the folder to delete
+     * @return void
+     * @throws \Box\Spout\Common\Exception\IOException If the folder path is not inside of the base folder
+     */
+    public function deleteFolderRecursively($folderPath);
+}