Magento which model is correct for getting the quote in the cart?

Question

I have tried every different combo of model that returns a quote in order to try and find the one that has the quote for the current customer's cart.

So far none of them work, and I can't figure out why this might be.

Essentially I'm running an external script in the misc directory that sets a generated coupon code on the current cart, but none of the following set the code correctly and I have to default to redirecting to /checkout/cart/coupon/post or whatever the correct url is for that.

Here are the different models I have tried for getting the session:

$session = Mage::getSingleton("customer/session");
$session = Mage::getSingleton('checkout/session');
$session = Mage::getSingleton('core/session');
$session = Mage::getSingleton("core/session",  array("name"=>"frontend"));

And these are the different method's I've tried to run on the quote:

$quote->getShippingAddress()->setCollectShippingRates(true);
$quote->setCartCouponCode($coupon);
$quote->setCouponCode($coupon);
$quote->collectTotals();
$quote->save();

They don't fail but they also do not set the code correctly.

Answer 1

Try this:

<?php
$mageFilename = 'app/Mage.php';
if (!file_exists($mageFilename)) {
    echo $mageFilename . " was not found";
    exit;
}
require_once $mageFilename;
Mage::app();

// This has to run to authenticate customer and checkout session calls.
Mage::getSingleton('core/session', array('name' => 'frontend'));

$quote = Mage::getSingleton('checkout/session')->getQuote();

$couponCode = "COUPON_TEST"; // Make sure to use the valid coupon here

$quote->getShippingAddress()->setCollectShippingRates(true);
$quote->setCouponCode($couponCode);
$quote->setTotalsCollectedFlag(false);
$quote->collectTotals();

$quote->save();

die("Applied coupon $couponCode successfully!");