Pesho the Pharmacist

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

function create_DateTime_from_date_string($dateString) {
    return DateTime::createFromFormat('d/m/Y H:i:s', $dateString . ' 00:00:00');
}

$today = create_DateTime_from_date_string($_GET['today']);
$farthestDate = clone $today;
date_sub($farthestDate, date_interval_create_from_date_string('5 years'));

$invoicesArr = $_GET['invoices'];
$invoiceList = array();
foreach ($invoicesArr as $invoice) {
    $invoiceData = explode('|', $invoice);
    $invoiceDateStr = trim($invoiceData[0]);
    $invoiceCompany = trim($invoiceData[1]);
    $invoiceDrug = trim($invoiceData[2]);
    $invoiceCost = (float)$invoiceData[3];

    $invoiceDateObj = create_DateTime_from_date_string($invoiceDateStr);
    if ($invoiceDateObj < $farthestDate || $invoiceDateObj > $today) {
        continue;
    }

    $invoiceDateOutput = $invoiceDateObj->format('Y/m/d');
    if (!array_key_exists($invoiceDateOutput, $invoiceList)) {
        $invoiceList[$invoiceDateOutput] = array();
    }

    if (!array_key_exists($invoiceCompany, $invoiceList[$invoiceDateOutput])) {
        $invoiceList[$invoiceDateOutput][$invoiceCompany] = array();
    }

    if (!array_key_exists($invoiceDrug, $invoiceList[$invoiceDateOutput][$invoiceCompany])) {
        $invoiceList[$invoiceDateOutput][$invoiceCompany][$invoiceDrug] = 0;
    }

    $invoiceList[$invoiceDateOutput][$invoiceCompany][$invoiceDrug] += $invoiceCost;
}

ksort($invoiceList);
echo '<ul>';
foreach ($invoiceList as $date => &$companies) {
    ksort($companies);
    echo '<li><p>' . substr($date, 8, 2) . substr($date, 4, 4) . substr($date, 0, 4) . '</p>';
    foreach ($companies as $company => &$medicine) {
        ksort($medicine);
        echo "<ul><li><p>{$company}</p>";
        $outArr = [];
        foreach ($medicine as $drug => $price) {
            $outArr[] = $drug;
        }
        echo '<ul><li><p>' . implode(',', $outArr) . '-' . array_sum($medicine) . 'lv</p></li></ul></li></ul>';
    }
    echo '</li>';
}
echo '</ul>';