I have only one product and I have to sell directly and not via product page or home page. When visiting the site URL it should directly add a product into the cart and redirect to checkout page.
You can add an observer to, for example, controller_action_predispatch
and check for products in the cart. However make sure the checkout URL's ship this.
The observer would look something like
public function checkProductAdded($o)
{
$cart = Mage::getModel('checkout/cart')->getQuote();
if (count($cart->getAllItems())) {
return $this;
}
$product = Mage::getModel('catalog/product')->load([id of product]);
$params = array('qty' => 1);
$cart->addProduct($product, $params);
$cart->save();
Mage::getSingleton('checkout/session')->setCartWasUpdated(true);
Mage::app()->getResponse()->setRedirect(Mage::getUrl("checkout/cart"));
}
Didn't test it but with a little tweaking it should work