Update quantity of the same item in the session instead of adding new one

Question

I use the following code in my controller for adding product items to the session:

$app = JFactory::getApplication();
$input = $app->input;
$itemid = $input->get('itemid');
$quan = $input->get('quan');
$session = JFactory::getSession();
$cart = $session->get('cart', array());
$cart['items'][] = array('itemid' => $itemid, 'quan' => $quan);
$session->set('cart', $cart);

It works, but if I add the same product with the same ID to the session once more it doesn't update the quantity of such product but adds the same product as new item. So I need something like:

if($itemid == 'itemid') {
    $cart['items'][] = array('quan' => 'quan'+$quan); // i.e. current quan + new quan
} else {
    $cart['items'][] = array('itemid' => $itemid, 'quan' => $quan);
}

It doesn't work of course

Answer 1

Solution A: Slightly adjusted array structure

You have only your itemid and the corresponding quantity in your array. Why don't you use the itemid as array index ($cart['items'][<ITEMID>]) so you could easily update your quantity if the index already exists.

$cart['items'][100] = 10
$cart['items'][236] = 5
  your itemid --^     ^-- your quantity

Something like

if (isset($cart['items'][$itemid]))
{
    $cart['items'][$itemid] = $cart['items'][$itemid] + $quan;
}
else 
{
    $cart['items'][$itemid] = $quan;
}

Solution B: Loop through existing array structure

Otherwise you have to loop through your array, find the item with the right itemid and update its quantity, like this:

$app = JFactory::getApplication();
$input = $app->input;
$itemid = $input->get('itemid');
$quan = $input->get('quan');
$session = JFactory::getSession();
$cart = $session->get('cart', array());
$found = false;

if (isset($cart['items']) && !empty($cart['items']))
{
    foreach ($cart['items'] as &$item)
    {
        if ($item['itemid'] == $itemid)
        {
            $item['quan'] += $quan;
            $found = true;
            break;
        }
    }
}

if (!$found) 
{
    $cart['items'][] = array('itemid' => $itemid, 'quan' => $quan);
}

$session->set('cart', $cart);