PHP: Dates

<?php 
$title = 'Contact us';
require 'header.php';
require_once 'config.php';
?>

<p class="lead mb-5">Lorem ipsum dolor sit, amet consectetur adipisicing elit. Adipisci cupiditate in iusto vel asperiores impedit non. Provident hic illum adipisci optio laboriosam consequuntur voluptatem, temporibus asperiores doloremque ratione atque facere!</p>
<div class="row">
  <div class="col-md-7">
    <h2 class="pb-3">Send us a message</h2>
    <form>
      <div class="form-group">
        <label for="exampleInputEmail1">Email address</label>
        <input type="email" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp" placeholder="Enter email">
        <small id="emailHelp" class="form-text text-muted">We'll never share your email with anyone else.</small>
      </div>
      <div class="form-group">
        <label for="exampleInputPassword1">Message</label>
        <textarea class="form-control" id="exampleInputPassword1" placeholder="Type your message"></textarea>
      </div>
      <button type="submit" class="btn btn-primary">Send</button>
    </form>
  </div>
  <div class="col-md-5">
    <h2 class="pb-3">Visit the shop</h2>
     <?php 
      $isOpen = contact_visit(TIMESLOTS);
      contact_visit_alert($isOpen);
      contact_visit_ul(TIMESLOTS, $isOpen);
     ?>
  </div>
</div>

<?php require 'footer.php'; ?>

<?php
function contact_visit($weekSlots): array
{
  $open['day'] = $open['hour'] = 0;
  $today = (int)date('w');
  $now = (int)date('G');  
  if(!empty($weekSlots[$today])) {
    (int)$open['day'] = 1;
  }
  foreach ($weekSlots[$today] as $slot) {
    if ($now >= $slot[0] && $now < $slot[1] ) {
      (int)$open['hour'] = 1;
    }
  }
  return $open;
}
function contact_visit_ul(array $weekSlots, array $isOpen): array
{
  foreach (DAYS as $d => $day) { 
    $style = '';
    if($d === (int)date('w')) {
      if($isOpen['hour'] === 1) { 
        $color = "green";
      } else {
        $color = "red";
      }
      $style = "style='color:$color'";
    }
    ?><li <?= $style ?> >
      <b><?= $day ?></b>: <?php
      if(empty($weekSlots[$d])) { 
        echo 'closed';
      } else {
        contact_visit_li($weekSlots[$d]);
      } ?>
    </li><?php
  }
  return $isOpen;
}
function contact_visit_li(array $daySlots)
{
  $line = [];
  foreach ($daySlots as $slot) {
    for ($i=0; $i<count($slot); $i++) { // Formating from 24-hour format to 12-hour Am format
      if($slot[$i] > 12) {
        $slot[$i] = ($slot[$i] - 12) . ' pm';
      } else {
        $slot[$i] .= ' am';
      }
    }
    $line[] = "$slot[0] - $slot[1]";
  }
  echo implode(' / ', $line);
}
function contact_visit_alert(array $isOpen) 
{
  if(array_sum($isOpen) === 2) {
    echo '<div class="alert alert-success" role="alert">The store is open.</div>';
  } else {
    echo '<div class="alert alert-danger" role="alert">The store is now closed, please come back tomorrow!</div>';
  }
}

function title_dyn(string $var = 'The Developer Fastlane'): void 
{
    if (isset($var)) {
        echo $var; 
    } else {
        echo 'The Developer Fastlane';
    }
}

function nav_item($link, $title, $aClass) 
{
  $class = 'nav-item';
  if (strpos($_SERVER["SCRIPT_NAME"], $link) !== false) {
    $class .= $class . ' active';
  }
    $html = '<li class="' . $class . '">
      <a class="' . $aClass . '" href="' . $link . '">' . $title . '</a>
    </li>';
  return $html;
}

function nav_menu(string $aClass=''): string
{
  return 
    nav_item('index.php', 'Home', $aClass) .
    nav_item('contact.php', 'Contact', $aClass);
}