engine/mainEngine.php

<?php
	class MainClass {
		private $mysqli;

		public $headTitle, $bodyTitle, $currentYear, $page;
		public function __construct($page) {
			$this -> mysqli = new mysqli('localhost', '*user*', '*pass*', '*db*');
			if ($page == '')
				$page = 'index';
			$this -> page = $page;
			$this -> initMainDetails();
		}
		public function initMainDetails() {
			$row = $this -> mysqli -> query('SELECT * FROM `content` WHERE `page` = "' . $this -> page . '";') -> fetch_assoc();
			$this -> headTitle = $row['headtitle'];
			$this -> bodyTitle = $row['bodytitle'];
			$this -> currentYear = date('Y');
		}
		public function displayContent() {
			require_once 'content/' . $this -> page . '.php';
		}
		public function getCatalogue($category) {
			$res = '';
			$sql = $this -> mysqli -> query('SELECT `id`, `title`, `price`, `img` FROM `' . $category . '` ORDER BY `id` DESC;');
			//print_r($sql);
			while($row = $sql -> fetch_assoc()) {
				$res .= '<article class="product">';
					$res .= '<a href="productview?category=' . $category . '&id=' . $row['id'] . '">';
						$res .= '<img src="" />';
					$res .= '</a>';
					$res .= '<p>' . $row['title'] . '</p>';
					$res .= '<p>' . $row['price'] . '</p>';
				$res .= '</article>';
			}
			return $res;
		}
	}
	$mainClass = new MainClass(explode('/', $_SERVER['REQUEST_URI'])[1]);
?>