tasks complete

src/main/kotlin/orders/Order.kt

@@ -18,21 +18,30 @@ class Order(
      */
     fun addProduct(product: Product?) {
         // TODO: add product to _products, ignore null
+        if (product != null) {
+            _products.add(product)
+        }
     }
 
     /**
      * Removes the first product matching [productId].
      */
     fun removeProductById(productId: Int) {
         // TODO: remove product from _products by id
+        _products.removeIf { it.id == productId }
+
+
     }
 
     /**
      * Returns the total price of all products in the order.
      */
     override fun calculateTotal(): Int {
-        // TODO: sum the prices of all products
-        return 0
+        var sum = 0
+        for (product in _products) {
+            sum += product.price
+        }
+        return sum
     }
 
     /**
@@ -41,6 +50,10 @@ class Order(
      */
     fun pay() {
         // TODO: throw if _products is empty, otherwise set status to Paid
+        if (_products.size==0){
+            throw IllegalStateException("empty")
+        }
+        else{status = OrderStatus.Paid}
     }
 
     /**
@@ -49,5 +62,9 @@ class Order(
      */
     fun cancel(reason: String?) {
         // TODO: set status to Cancelled with reason (default "Unknown reason" if null)
+        if (reason!=null){
+            status= OrderStatus.Cancelled(reason)
+        }
+        status= OrderStatus.Cancelled("Unknown reason")
     }
 }

src/main/kotlin/orders/OrderExtensions.kt

@@ -14,5 +14,13 @@ fun Order.applyDiscount(
     discountPercent: Int,
     logger: ((String) -> Unit)? = null
 ) {
-    // TODO: apply discount to each product using extension + scoped functions
-}
+    products.toList().forEach { product ->
+        removeProductById(product.id)
+
+        val discountedPrice = (product.price * (100 - discountPercent) / 100)
+        val discountedProduct = product.copy(price = discountedPrice)
+
+        addProduct(discountedProduct)
+        logger?.invoke("${product.name} ${product.price} is now $discountedPrice")
+    }
+}

src/main/kotlin/orders/OrderProcessor.kt

@@ -9,5 +9,9 @@ package orders
  */
 fun processOrder(order: Order): String {
     // TODO: use when to return the appropriate string
-    return ""
+    return when (val status = order.status) {
+        OrderStatus.Created -> "Order ${order.id} is new"
+        OrderStatus.Paid -> "Order ${order.id} is paid"
+        is OrderStatus.Cancelled -> "Order ${order.id} is cancelled: ${status.reason}"
+    }
 }