hw1 completed

build.gradle.kts

@@ -2,6 +2,10 @@ plugins {
     kotlin("jvm") version "2.1.0"
 }
 
+kotlin {
+    jvmToolchain(21)
+}
+
 group = "orders"
 version = "1.0"
 

src/main/kotlin/orders/Order.kt

@@ -17,37 +17,45 @@ class Order(
      * If the product is null, it should be ignored.
      */
     fun addProduct(product: Product?) {
-        // TODO: add product to _products, ignore null
+        product?.let {
+            _products.add(it)
+        }
     }
 
     /**
      * Removes the first product matching [productId].
      */
     fun removeProductById(productId: Int) {
-        // TODO: remove product from _products by id
+        val productToRemove = _products.find { it.id == productId }
+        productToRemove?.let {
+            _products.remove(it)
+        }
     }
 
     /**
      * Returns the total price of all products in the order.
      */
     override fun calculateTotal(): Int {
-        // TODO: sum the prices of all products
-        return 0
+        return _products.sumOf { it.price }
     }
 
     /**
      * Marks the order as paid.
      * Throws [IllegalStateException] if the order has no products.
      */
     fun pay() {
-        // TODO: throw if _products is empty, otherwise set status to Paid
+        if (_products.isEmpty()) {
+            throw IllegalStateException("Cannot pay for an empty order")
+        }
+        status = OrderStatus.Paid
     }
 
     /**
      * Cancels the order with the given reason.
      * If [reason] is null, use "Unknown reason".
      */
     fun cancel(reason: String?) {
-        // TODO: set status to Cancelled with reason (default "Unknown reason" if null)
+        val finalReason = reason ?: "Unknown reason"
+        status = OrderStatus.Cancelled(finalReason)
     }
 }

src/main/kotlin/orders/OrderExtensions.kt

@@ -14,5 +14,15 @@ fun Order.applyDiscount(
     discountPercent: Int,
     logger: ((String) -> Unit)? = null
 ) {
-    // TODO: apply discount to each product using extension + scoped functions
-}
+    val currentProducts = products.toList()
+    for (product in currentProducts) {
+        val discountAmount = (product.price * discountPercent) / 100
+        val newPrice = product.price - discountAmount
+        val discountedProduct = product.copy(price = newPrice)
+        discountedProduct.also {
+            logger?.invoke("Discount applied for ${it.name}: ${product.price} -> ${it.price}")
+        }
+        removeProductById(product.id)
+        addProduct(discountedProduct)
+    }
+}

src/main/kotlin/orders/OrderProcessor.kt

@@ -8,6 +8,9 @@ package orders
  *   - Cancelled -> "Order {id} is cancelled: {reason}"
  */
 fun processOrder(order: Order): String {
-    // TODO: use when to return the appropriate string
-    return ""
-}
+    return when (val status = order.status) {
+        is OrderStatus.Created -> "Order ${order.id} is new"
+        is OrderStatus.Paid -> "Order ${order.id} is paid"
+        is OrderStatus.Cancelled -> "Order ${order.id} is cancelled: ${status.reason}"
+    }
+}