diff --git a/.idea/.name b/.idea/.name
new file mode 100644
index 0000000..c9afd04
--- /dev/null
+++ b/.idea/.name
@@ -0,0 +1 @@
+KotlinHomework
\ No newline at end of file
diff --git a/.idea/codeStyles/Project.xml b/.idea/codeStyles/Project.xml
new file mode 100644
index 0000000..7643783
--- /dev/null
+++ b/.idea/codeStyles/Project.xml
@@ -0,0 +1,123 @@
+<component name="ProjectCodeStyleConfiguration">
+  <code_scheme name="Project" version="173">
+    <JetCodeStyleSettings>
+      <option name="CODE_STYLE_DEFAULTS" value="KOTLIN_OFFICIAL" />
+    </JetCodeStyleSettings>
+    <codeStyleSettings language="XML">
+      <option name="FORCE_REARRANGE_MODE" value="1" />
+      <indentOptions>
+        <option name="CONTINUATION_INDENT_SIZE" value="4" />
+      </indentOptions>
+      <arrangement>
+        <rules>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>xmlns:android</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>^$</XML_NAMESPACE>
+                </AND>
+              </match>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>xmlns:.*</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>^$</XML_NAMESPACE>
+                </AND>
+              </match>
+              <order>BY_NAME</order>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>.*:id</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>http://schemas.android.com/apk/res/android</XML_NAMESPACE>
+                </AND>
+              </match>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>.*:name</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>http://schemas.android.com/apk/res/android</XML_NAMESPACE>
+                </AND>
+              </match>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>name</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>^$</XML_NAMESPACE>
+                </AND>
+              </match>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>style</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>^$</XML_NAMESPACE>
+                </AND>
+              </match>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>.*</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>^$</XML_NAMESPACE>
+                </AND>
+              </match>
+              <order>BY_NAME</order>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>.*</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>http://schemas.android.com/apk/res/android</XML_NAMESPACE>
+                </AND>
+              </match>
+              <order>ANDROID_ATTRIBUTE_ORDER</order>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>.*</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>.*</XML_NAMESPACE>
+                </AND>
+              </match>
+              <order>BY_NAME</order>
+            </rule>
+          </section>
+        </rules>
+      </arrangement>
+    </codeStyleSettings>
+    <codeStyleSettings language="kotlin">
+      <option name="CODE_STYLE_DEFAULTS" value="KOTLIN_OFFICIAL" />
+    </codeStyleSettings>
+  </code_scheme>
+</component>
\ No newline at end of file
diff --git a/.idea/codeStyles/codeStyleConfig.xml b/.idea/codeStyles/codeStyleConfig.xml
new file mode 100644
index 0000000..79ee123
--- /dev/null
+++ b/.idea/codeStyles/codeStyleConfig.xml
@@ -0,0 +1,5 @@
+<component name="ProjectCodeStyleConfiguration">
+  <state>
+    <option name="USE_PER_PROJECT_SETTINGS" value="true" />
+  </state>
+</component>
\ No newline at end of file
diff --git a/.idea/deploymentTargetSelector.xml b/.idea/deploymentTargetSelector.xml
deleted file mode 100644
index b268ef3..0000000
--- a/.idea/deploymentTargetSelector.xml
+++ /dev/null
@@ -1,10 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="deploymentTargetSelector">
-    <selectionStates>
-      <SelectionState runConfigName="app">
-        <option name="selectionMode" value="DROPDOWN" />
-      </SelectionState>
-    </selectionStates>
-  </component>
-</project>
\ No newline at end of file
diff --git a/.idea/gradle.xml b/.idea/gradle.xml
index 589fc7f..444059e 100644
--- a/.idea/gradle.xml
+++ b/.idea/gradle.xml
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="GradleMigrationSettings" migrationVersion="1" />
   <component name="GradleSettings">
     <option name="linkedExternalProjectsSettings">
       <GradleProjectSettings>
diff --git a/.idea/markdown.xml b/.idea/markdown.xml
new file mode 100644
index 0000000..c61ea33
--- /dev/null
+++ b/.idea/markdown.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="MarkdownSettings">
+    <option name="previewPanelProviderInfo">
+      <ProviderInfo name="Compose (experimental)" className="com.intellij.markdown.compose.preview.ComposePanelProvider" />
+    </option>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/misc.xml b/.idea/misc.xml
index 74dd639..b2c751a 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -1,4 +1,3 @@
-<?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="ExternalStorageConfigurationManager" enabled="true" />
   <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="jbr-21" project-jdk-type="JavaSDK">
diff --git a/build.gradle.kts b/build.gradle.kts
index a2cfebb..cd4d9d8 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -2,6 +2,10 @@ plugins {
     kotlin("jvm") version "2.1.0"
 }
 
+kotlin {
+    jvmToolchain(21)
+}
+
 group = "orders"
 version = "1.0"
 
diff --git a/src/main/kotlin/orders/Order.kt b/src/main/kotlin/orders/Order.kt
index 8a6c82a..58e6955 100644
--- a/src/main/kotlin/orders/Order.kt
+++ b/src/main/kotlin/orders/Order.kt
@@ -17,22 +17,26 @@ 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 }
     }
 
     /**
@@ -40,7 +44,10 @@ class Order(
      * 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
     }
 
     /**
@@ -48,6 +55,7 @@ class Order(
      * 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)
     }
 }
diff --git a/src/main/kotlin/orders/OrderExtensions.kt b/src/main/kotlin/orders/OrderExtensions.kt
index d644b59..5415f4a 100644
--- a/src/main/kotlin/orders/OrderExtensions.kt
+++ b/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)
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/orders/OrderProcessor.kt b/src/main/kotlin/orders/OrderProcessor.kt
index b2bd34d..927c222 100644
--- a/src/main/kotlin/orders/OrderProcessor.kt
+++ b/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}"
+    }
+}
\ No newline at end of file