Add support to shipping cost

CartPositionInterface.php

@@ -15,6 +15,8 @@ interface CartPositionInterface
 {
     /** Triggered on cost calculation */
     const EVENT_COST_CALCULATION = 'costCalculation';
+    /** Triggered on after cart shipping calculation */
+    const EVENT_SHIPPING_COST_CALCULATION = 'shippingCostcalculation';
 
     /**
      * @return integer
@@ -40,5 +42,5 @@ public function setQuantity($quantity);
     /**
      * @return int
      */
-    public function getQuantity();
+    public function getQuantity();  
 } 

README.md

@@ -217,3 +217,63 @@ $cart->on(ShoppingCart::EVENT_COST_CALCULATION, function ($event) {
     $event->discountValue = 100;
 });
 ```
+
+5. During the calculation the following events are triggered: 
+- `ShoppingCart::EVENT_COST_CALCULATION` once per calculation.
+- `CartPositionInterface::EVENT_COST_CALCULATION` for each position in the cart.
+
+You can also subscribe on this events to perform discount calculation:
+
+```php
+$cart->on(ShoppingCart::EVENT_COST_CALCULATION, function ($event) {
+    $event->discountValue = 100;
+});
+```
+
+
+Using shipping cost
+---------------
+
+Shipping costs are implemented as behaviors that could attached to the cart or it's positions. To use them, follow this steps:
+
+1. Define discount class as a subclass of yz\shoppingcart\ShippingCostBehavior
+
+```php
+// app/components/FixedShippingCost.php
+
+class FixedShippingCost extends ShippingCostBehavior
+{
+    public $freeSince = 0;
+    public $ammount = 0;
+
+    /**
+     * @param ShippingCostCalculationEvent $event
+     */
+    public function onShippingCostCalculation($event)
+    {
+        if($this->owner->getCost() < $this->freeSince)
+            $event->shippingValue = $this->ammount;
+        else
+            $event->shippingValue = 0;
+    }
+}
+```
+
+2. Add this behavior to the cart:
+
+```php
+$cart->attachBehavior('fixedShippingCost', ['class' => 'app\components\FixedShippingCost', 'ammount' => 10, 'freeSince' => 999]);
+```
+
+3. To get shipping cost with discount applied:
+
+```php
+$cost = \Yii::$app->cart->getShippingCost(true);
+```
+
+4. To get cart total:
+
+```php
+$total = \Yii::$app->cart->getTotal(true);
+```
+

ShippingCostBehavior.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace yz\shoppingcart;
+
+use yii\base\Behavior;
+
+
+/**
+ * Class ShippingCostBehavior
+ * @package \yz\shoppingcart
+ */
+class ShippingCostBehavior extends Behavior
+{
+    public function events()
+    {
+        return [
+            ShoppingCart::EVENT_SHIPPING_COST_CALCULATION => 'onShippingCostCalculation',
+        ];
+    }
+
+    /**
+     * @param CostCalculationEvent $event
+     */
+    public function onShippingCostCalculation($event)
+    {
+
+    }
+}

ShippingCostCalculationEvent.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace yz\shoppingcart;
+
+use yii\base\Event;
+
+
+/**
+ * Class ShippingCostCalculationEvent
+ * @package \yz\shoppingcart
+ */
+class ShippingCostCalculationEvent extends Event
+{
+    /**
+     * Shipping value that could be filled by the cart's behaviors that should provide shippings methods.
+     * This value will be added to the cart's cost
+     * @var float
+     */
+    public $shippingValue = 0;
+} 

ShoppingCart.php

@@ -32,6 +32,8 @@ class ShoppingCart extends Component
     const EVENT_CART_CHANGE = 'cartChange';
     /** Triggered on after cart cost calculation */
     const EVENT_COST_CALCULATION = 'costCalculation';
+    /** Triggered on after cart shipping calculation */
+    const EVENT_SHIPPING_COST_CALCULATION = 'shippingCostcalculation';
 
     /**
      * If true (default) cart will be automatically stored in and loaded from session.
@@ -278,6 +280,34 @@ public function getCost($withDiscount = false)
         return $cost;
     }
 
+    /**
+     * Return full cart shipping cost
+     * @param $withDiscount
+     * @return int
+     */
+    public function getShippingCost($withDiscount = false)
+    {
+        $cost = $this->getCost($withDiscount);
+
+        $shippingCostEvent = new ShippingCostCalculationEvent([]);
+        $this->trigger(self::EVENT_SHIPPING_COST_CALCULATION, $shippingCostEvent);
+        $cost = $shippingCostEvent->shippingValue;
+        return $cost;
+    }
+
+    /**
+     * Return full cart total cost
+     * @param $withDiscount
+     * @return int
+     */
+    public function getTotal($withDiscount = false)
+    {
+        $cost = $this->getCost($withDiscount);
+        $shipping = $this->getShippingCost($withDiscount);
+
+        return $cost + $shipping;
+    }
+
     /**
      * Returns hash (md5) of the current cart, that is unique to the current combination
      * of positions, quantities and costs. This helps us fast compare if two carts are the same, or not, also