<?php
class ShoppingCart {
    protected $items = array();
    
    public function AddItem($product_id) {
        if(array_key_exists($product_id, $this->items)) {
            $this->items[$product_id] = $this->items[$product_id] + 1;
        }
        else {
            $this->items[$product_id] = 1;
        }
    }
    
    public function GetItemCost($product_id) {
        $cost_string = get_item_cost($product_id);
        $cost_float = "$cost_string" + 0;
        
        return $cost_float * $this->GetItemQuantity($product_id);
    }
    
    public function GetItemShippingCost($product_id) {
        return $this->GetItemQuantity($product_id) * $this->getShippingCostFor(get_item_cost($product_id));
    }
    
    private function getShippingCostFor($price) {
        if ($price < 10) {
            return 1.99;
        }
        elseif ($price < 50) {
            return 10.99;
        }
        else {
            return 34.99;
        }
    }
    
    public function GetItems() {
        return array_keys($this->items);
    }
    
    public function GetItemQuantity($product_id) {
        return intval($this->items[$product_id]);
    }
    
    public function EmptyCart() {
        $this->items = array();
    }
}
?>

<?php
// DEFINE GLOBALS

define ('STORE_XML_FILE', '../catalog.xml');

// DEFINE REFERENCES

require_once ('templates.php');

require_once ('../classes/ShoppingCart.php');

// FUNCTIONS
session_start();

function get_xml_catalog() {
    return new SimpleXMLElement(file_get_contents(STORE_XML_FILE));
}

function get_item_cost($product_id) {
    foreach(get_xml_catalog() as $product) {
        if ($product_id == $product->id) {
            return $product->price;
        }
    }
    throw new Exception('item not found: ' . $product_id);
}

function product_exists($product_id) {
    foreach(get_xml_catalog() as $product) {
        if ($product->id == $product_id)
            return true;
    }
    return false;
}

function get_shopping_cart() {
    if (!isset($_SESSION['cart'])){
        return new ShoppingCart();
    }
    else
        return unserialize($_SESSION['cart']);
}

function set_shopping_cart($cart) {
    $_SESSION['cart'] = serialize($cart);
}
?>