Convert BillingService to Kotlin

library/src/main/java/com/billing/BillingService.kt

@@ -0,0 +1,75 @@
+package com.billing
+
+import android.app.Activity
+import androidx.annotation.CallSuper
+
+abstract class BillingService {
+
+    private val purchaseServiceListeners: MutableList<PurchaseServiceListener> = mutableListOf()
+    private val subscriptionServiceListeners: MutableList<SubscriptionServiceListener> = mutableListOf()
+
+    fun addPurchaseListener(purchaseServiceListener: PurchaseServiceListener) {
+        purchaseServiceListeners.add(purchaseServiceListener)
+    }
+
+    fun removePurchaseListener(purchaseServiceListener: PurchaseServiceListener) {
+        purchaseServiceListeners.remove(purchaseServiceListener)
+    }
+
+    fun addSubscriptionListener(subscriptionServiceListener: SubscriptionServiceListener) {
+        subscriptionServiceListeners.add(subscriptionServiceListener)
+    }
+
+    fun removeSubscriptionListener(subscriptionServiceListener: SubscriptionServiceListener) {
+        subscriptionServiceListeners.remove(subscriptionServiceListener)
+    }
+
+    /**
+     * @param sku       - product specificator
+     * @param isRestore - a flag indicating whether it's a fresh purchase or restored product
+     */
+    fun productOwned(sku: String?, isRestore: Boolean) {
+        for (purchaseServiceListener in purchaseServiceListeners) {
+            if (isRestore) {
+                purchaseServiceListener.onProductRestored(sku)
+            } else {
+                purchaseServiceListener.onProductPurchased(sku)
+            }
+        }
+    }
+
+    /**
+     * @param sku       - subscription specificator
+     * @param isRestore - a flag indicating whether it's a fresh purchase or restored subscription
+     */
+    fun subscriptionOwned(sku: String, isRestore: Boolean) {
+        for (subscriptionServiceListener in subscriptionServiceListeners) {
+            if (isRestore) {
+                subscriptionServiceListener.onSubscriptionRestored(sku)
+            } else {
+                subscriptionServiceListener.onSubscriptionPurchased(sku)
+            }
+        }
+    }
+
+    fun updatePrices(iapkeyPrices: Map<String, String>) {
+        for (billingServiceListener in purchaseServiceListeners) {
+            billingServiceListener.onPricesUpdated(iapkeyPrices)
+        }
+        for (billingServiceListener in subscriptionServiceListeners) {
+            billingServiceListener.onPricesUpdated(iapkeyPrices)
+        }
+    }
+
+    abstract fun init(key: String?)
+    abstract fun buy(activity: Activity, sku: String)
+    abstract fun subscribe(activity: Activity, sku: String)
+    abstract fun unsubscribe(activity: Activity, sku: String)
+    abstract fun enableDebugLogging(enable: Boolean)
+
+    @CallSuper
+    open fun close() {
+        subscriptionServiceListeners.clear()
+        purchaseServiceListeners.clear()
+    }
+}