A converter of URL to URL with "campaign" query parameters

UrlCampaignBuilderService.php

<?php
/**
 * PHPUnit test suite available at:
 * https://gist.github.com/mylk/33e3d0e49152cf6b74362dc8a09b9d39
 */

/*
 * Installation (Symfony):
 * =======================
 * # services.yml
 * services:
 *     # ...
 *     acme.url_campaign_builder:
 *       class: Acme\AcmeBundle\Service\UrlCampaignBuilderService
 * 
 * Usage (Symfony):
 * ================
 * $campaignParameters = array(
 *     "source" => "newsletter",
 *     "medium" => "email",
 *     "campaign" => "august"
 * );
 * 
 * $urlCampaignBuilder = $this->get("acme.url_campaign_builder");
 * $urlCampaigned = $urlCampaignBuilder->build("http://www.google.com", $campaignParameters);
 */

namespace Acme\AcmeBundle\Service;

class UrlCampaignBuilderService
{
    /**
     * Builds a campaign URL and addresses some cases.
     *
     * @param string $url
     * @param array $parameters Usually one of "source", "medium", "campaign" but can be anything
     *
     * @return string|null
     */
    public function build($url, $parameters)
    {
        if (!$url) {
            return null;
        }

        $urlParsed = \parse_url($url);
        
        // if no scheme exists (http) the "host" by default is placed in "path"
        if (!isset($urlParsed["host"])) {
            $urlParsed["host"] = $urlParsed["path"];
            $urlParsed["path"] = "/";
        }

        if (!isset($urlParsed["scheme"])) {
            $urlParsed["scheme"] = "http";
        }

        if (!isset($urlParsed["path"])) {
            $urlParsed["path"] = "/";
        }

        if (!isset($urlParsed["query"])) {
            $urlParsed["query"] = "";
        } else {
            $urlParsed["query"] .= "&";
        }

        $campaignParameters = "";
        foreach ($parameters as $parameterKey => $parameterValue) {
            $campaignParameters .= \sprintf("&utm_%s=%s", $parameterKey, $parameterValue);
        }
        // remove the first "&" character
        $campaignParameters = \substr($campaignParameters, 1, \strlen($campaignParameters) - 1);

        // append to the original query
        $urlParsed["query"] .= $campaignParameters;

        $urlWithCampaign = \sprintf("%s://%s%s?%s", $urlParsed["scheme"], $urlParsed["host"], $urlParsed["path"], $urlParsed["query"]);

        return $urlWithCampaign;
    }
}