Normalize relative path to absolute path

normalize-path.php

<?php

function normalize_url( $url ) {
	$delete = 0;
	$index = 0;
	$parts = explode( '/', $url );

	foreach ( $parts as $p => $part ) {
		if ( '..' === $part ) {
			$delete++;
			$index++;
		} elseif ( $delete ) {
			$offset = $index - $delete * 2;
			// Negative offset means an incorrect path
			if ( 0 === $offset ) {
				$index++;
				$delete = 0;
			} else {
				array_splice( $parts, $offset, $delete * 2 );
				$index -= $delete;
				$delete = 0;
			}
		} else {
			$index++;
		}
	}

	return implode( '/', $parts );
}

$test = array(
	'http://kaspars.net/one/about/two/../three/another/../../style.css' => 'http://kaspars.net/one/about/style.css',
	'http://kaspars.net/theme/../style.css' => 'http://kaspars.net/style.css',
	'/home/folder/../style.css' => '/home/style.css',
	'./home/../style.css' => './style.css',
	'/home/subfolder/../../../toomuch/style.css' => '/home/subfolder/../../../toomuch/style.css',
);

$results = array();

foreach ( $test as $url => $expected ) {
	$results[ $url ] = normalize_url( $url );
}

$errors = array_diff_assoc( $results, $test );

print_r( $errors ); // should be empty