Enable est column width calculation

src/Spout/Writer/Common/Helper/AppendHelper.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace Box\Spout\Writer\Common\Helper;
+
+class AppendHelper {
+
+    /**
+     * Instead of seeking and re-writing from position, a better hack might be to write dummy empty data
+     * Enough to take care of any length, then carefully overwrite
+     * 
+     */
+
+    /**
+     * This function will truncate from specified position
+     * Write data to be inserted and re-append the truncated data
+     *  
+     * @param $fp Pointer to file only
+     * @param $pos Position to insert
+     * @param $content Content to insert
+     */
+    public static function insertToFile($fp, $pos, $content)
+    {
+        fseek($fp, $pos);
+        $trailer = stream_get_contents($fp);
+        ftruncate($fp, $pos);
+        fseek($fp, $pos);
+        fwrite($fp, $content);
+        fwrite($fp, $trailer);
+        return $fp;
+    }
+}