<?php
/**
 * wp_parse_url is only available in WP 4.4. This ensures the function is available regardles of the WP version.
 */
if ( ! function_exists( 'wp_parse_url' ) ) {
    function wp_parse_url( $url ) {
        $parts = @parse_url( $url );
        if ( ! $parts ) {
            // < PHP 5.4.7 compat, trouble with relative paths including a scheme break in the path
            if ( '/' == $url[0] && false !== strpos( $url, '://' ) ) {
                // Since we know it's a relative path, prefix with a scheme/host placeholder and try again
                if ( ! $parts = @parse_url( 'placeholder://placeholder' . $url ) ) {
                    return $parts;
                }
                // Remove the placeholder values
                unset( $parts['scheme'], $parts['host'] );
            } else {
                return $parts;
            }
        }

        // < PHP 5.4.7 compat, doesn't detect schemeless URL's host field
        if ( '//' == substr( $url, 0, 2 ) && ! isset( $parts['host'] ) ) {
            $path_parts = explode( '/', substr( $parts['path'], 2 ), 2 );
            $parts['host'] = $path_parts[0];
            if ( isset( $path_parts[1] ) ) {
                $parts['path'] = '/' . $path_parts[1];
            } else {
                unset( $parts['path'] );
            }
        }

        return $parts;
    }
}