Pesho-the-Pharmacist

    <?php
        date_default_timezone_set('Europe/Sofia');

        $today = new DateTime($_GET['today']);
        $invoices = [];
        foreach ($_GET['invoices'] as $key => $row) {
            $invoices[] = preg_split('/\s*\|\s*/', $row, -1, PREG_SPLIT_NO_EMPTY);
            $invoices[$key][0] = DateTime::createFromFormat('d/m/Y', $invoices[$key][0]);
            preg_match('/\d+\.*\d*/', $invoices[$key][3], $invoices[$key][3]);
            $invoices[$key][3] = $invoices[$key][3][0];
        }

        //clean unnecessary dates:
        foreach ($invoices as $key => $value) {
            $diffBetweenDates = $today->diff($value[0]);
            if ($diffBetweenDates->days >= 1826) {
                unset($invoices[$key]);
            }
        }

        // Obtain a list of keys for sorting:
        foreach ($invoices as $key => $row) {
            $sortDate[$key] = $row[0];
            $sortCompany[$key] = $row[1];
        }
        // Sort the data:
        array_multisort($sortDate, SORT_ASC, $sortCompany, SORT_ASC, $invoices );

        $invoiceResultArr = fillResultArray($invoices);

        //print result:
        echo '<ul>';
        foreach ($invoiceResultArr as $date => $value) {
            echo '<li><p>' . $date . '</p>';
            echo '<ul>';
            foreach ($invoiceResultArr[$date] as $company => $order) {
                echo '<li><p>' . $company . '</p>';
                echo '<ul>';
                echo '<li><p>' . implode(',', $order['products']) . '-' . $order['total'] . 'lv</p></li>';
                echo '</ul></li>';
            }
            echo '</ul>';
            echo '</li>';
        }
        echo '</ul>';

        function fillResultArray($array) {
            $resultArray = [];
            foreach ($array as $key => $value) {
                $date = $value[0]->format('d/m/Y');
                if (!key_exists($date, $resultArray)) {
                    $resultArray[$date] = [];
                }
                if (!key_exists($value[1], $resultArray[$date])) {
                    $resultArray[$date][$value[1]] = array('products' => [], 'total' => 0);
                }
                $resultArray[$date][$value[1]]['products'][] = $value[2];
                $resultArray[$date][$value[1]]['total'] += $value[3];
            }
            return $resultArray;
        }
        ?>