An example of how an external package containing pure domain logic can be cleanly integrated into different applications

legacy-app-index.php

<?php
//FILE: legacy-application/public/index.php

require_once __DIR__ . '/../vendor/autoload.php';

$config = require __DIR__ . '../config/settings.php';
$counties = require __DIR__ . '/../vendor/my-company/my-package/src/counties.php';

$app = \App\Application::createFromConfig($config, $counties);

$byEntity = isset($_GET['ByEntity']) ? $_GET['ByEntity'] : null;
$byCategory = isset($_GET['ByType']) ? $_GET['ByType'] : null;
$byCounty = isset($_GET['County']) ? $_GET['County'] : null;

echo $app->template('header'); ?>
<?php
if (!$app->resultsCanBeDisplayed()) {
    echo $app->template('see_official_results');
} else {
    if ($byEntity) {
        $result = $app->results()->getResultsForEntity($byEntity, false);
        echo $app->template('some-entity/single', compact('byEntity', 'result'));
    } elseif ($byCategory) {
        $results = $app->results()->getResultsForCategory($byCategory);
        echo $app->template('some-entity/all', compact('results', 'byCategory'));
    } elseif ($byCounty) {
        $entities = $app->results()->getResultsForCounty($byCounty);
        $totalByEntity = $app->results()->getTotalVotesByEntity($byCounty);
        echo $app->template('some-entity/by_county', compact('byCounty', 'entities', 'totalsByEntity'));
    } else {
        echo $app->template('homepage');
    }
}

legacy-app-src-Application.php

<?php
//File: legacy-application/src/Application.php
namespace App;

use DateTime;
use Enr\Container;
use Enr\Domain\SomeEntity\EntityResultsRepository;

class Application
{
    /* properties, other methods omitted for brevity */

    public function __construct(Container $enrContainer, DateTime $displayDisabledAfter, $templatePath, $showTestingHeader = false)
    {
        $this->enrContainer = $enrContainer;
        $this->displayDisabledAfter = $displayDisabledAfter;
        $this->setTemplatePath($templatePath);
        $this->showTestingHeader = $showTestingHeader;
    }

    /**
    * @return EntityResultsRepository
    */
    public function results()
    {
        return $this->enrContainer->results();
    }

    /**
     * Creates a new Application instance from a standard configuration array
     *
     * @param array $config
     * @param array $counties
     * @return Application
     */
    public static function createFromConfig(array $config, array $counties)
    {
        $app = new static(
            new Container($config['enr_config'], $counties),
            DateTime::createFromFormat('Y-m-d', $config['display_disabled_after']),
            $config['template_path'],
            $config['show_testing_header']
        );
        if ($config['debug']) {
            $app->registerErrorHandler();
        }
        return $app;
    }
}

my-package-src-Container.php

<?php
namespace Enr;

class Container
{
    /* properties, other methods omitted for brevity */
    
    public function __construct(array $config, array $counties)
    {
        $this->config = $config;
        $this->counties = $counties;
    }
    
    /**
     * @return \Enr\Domain\SomeEntity\EntityResultsRepository
     */
    public function results()
    {
        return $this->getRepoFactory()->makeResultsRepo();
    }
}

slim-3-app-dependencies.php

<?php
//FILE: slim-3-app/config/dependencies.php

use Enr\Container as EnrContainer;
use Enr\SomeEntity\EntityResultsRepository;

$container = $app->getContainer();

$container[ EnrContainer::class ] = function($c) {
    $config = $c->get('enr_config');
    $counties = require __DIR__ . '/../vendor/my-company/my-package/src/counties.php';
    return new EnrContainer($config, $counties);
};

//Entity Results Repository
$container[ EntityResultsRepository::class ] = function($c) {
    return $c->get(EnrContainer::class)->results();
};

slim-3-app-index.php

<?php
// FILE: slim-3-app/public/index.php

if (PHP_SAPI == 'cli-server') {
    // To help the built-in PHP dev server, check if the request was actually for
    // something which should probably be served as a static file
    $url  = parse_url($_SERVER['REQUEST_URI']);
    $file = __DIR__ . $url['path'];
    if (is_file($file)) {
        return false;
    }
}

require __DIR__ . '/../vendor/autoload.php';

session_start();

// Instantiate the app
$settings = require __DIR__ . '/../config/settings.php';
$app = new \Slim\App($settings);

// Set up dependencies
require __DIR__ . '/../config/dependencies.php';

// Register middleware
require __DIR__ . '/../config/middleware.php';

// Register routes
require __DIR__ . '/../config/routes.php';

// Run app
$app->run();