Code indentation shifter : Shift code to the left, preserving indentation

CodeIndentationShifter.php

<?php
/**
 * Shift code to the left, preserving indentation.
 * 
 * This is useful when reading code extract in a not-displayed nested structures.
 * There is no use of closure here in order to remain compatible with older versions of PHP.
 * This method is code agnostic.
 * @example
 * $code = "";
 * $code .= "    while ($a) {";
 * $code .= "      if ($b) {";
 * $code .= "        echo $c;";
 * $code .= "      }";
 * $code .= "    }";
 * $cis = new CodeIndentationShifter();
 * echo $cis->shift($code);
 * Displays:
 * while ($a) {
 *   if ($b) {
 *     echo $c;
 *   }
 * }
 */
class CodeIndentationShifter {
	private $minIndent = null;

	/**
	 * Shift the provided content
	 * @param string The code content to shift
	 * @return string The shifted content
	 */
	public function shift($content) {
		$content = explode("\n", str_replace("\r\n", "\n", $content));
		$this->minIndent = null;
		array_map(array($this, "whiteSpacesCount"), $content);
		return implode("\n", array_map(array($this, "removeStartingWhiteSpaces"), $content));
	}

	/**
	 * Store the white spaces amount in the provided code line into $this::minIndent if it is smaller
	 * @param string $line A code line
	 */
	private function whiteSpacesCount($line) {
		if (trim($line) === "") return;
		$startingSpacesCount = strlen($line) - strlen(ltrim($line));
		if ($this->minIndent === null || $this->minIndent > $startingSpacesCount)
			$this->minIndent = $startingSpacesCount;
		return;
	}

	/**
	 * Remove the mininum amount from the provided line
	 * @param string $line A code line
	 * @return string The line, without the first not needed white spaces
	 */
	private function removeStartingWhiteSpaces($line) {
		return substr($line, $this->minIndent, strlen($line) - $this->minIndent);
	}
}

/*
// Test part:
$content = "  23146544;
 12321465487;
   3654654;

     587997;
 156654;
   3565654;
03354654;";

$cis = new CodeIndentationShifter();
echo $cis->shift($content);
*/
?>