Convert RenderUnitIdGenerator to Kotlin

Summary: As per title

Reviewed By: zielinskimz

Differential Revision: D45039980

fbshipit-source-id: 987b962e94db3e5ebfda75dc323d73f709b9af43

litho-core/src/main/java/com/facebook/litho/RenderUnitIdGenerator.kt

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.facebook.litho
+
+import androidx.annotation.GuardedBy
+import java.util.HashMap
+import java.util.concurrent.atomic.AtomicInteger
+
+/**
+ * Class that handles generation of unique IDs for RenderUnits for a given ComponentTree. The ID
+ * generation uses the component key to create an ID, and creates unique IDs for any components
+ * under the same ComponentTree.
+ */
+class RenderUnitIdGenerator(
+    /** Returns the ComponentTree ID that this ID-generator is linked with. */
+    val componentTreeId: Int
+) {
+
+  private val nextId = AtomicInteger(1)
+
+  @GuardedBy("this") private val keyToId = HashMap<String, Int>()
+
+  /**
+   * Calculates a returns a unique ID for a given component key and output type. The IDs will be
+   * unique for components in the ComponentTree this ID generator is linked with. If an ID was
+   * already generated for a given component, the same ID will be returned. Otherwise, a new unique
+   * ID will be generated
+   *
+   * @param componentKey The component key
+   * @param type The output type @see OutputUnitType
+   */
+  fun calculateLayoutOutputId(componentKey: String, @OutputUnitType type: Int): Long =
+      addTypeAndComponentTreeToId(getId(componentKey), type, componentTreeId)
+
+  @Synchronized
+  private fun getId(key: String): Int = keyToId.getOrPut(key) { nextId.getAndIncrement() }
+
+  companion object {
+    private fun addTypeAndComponentTreeToId(
+        id: Int,
+        @OutputUnitType type: Int,
+        componentTreeId: Int
+    ): Long = id.toLong() or (type.toLong() shl 32) or (componentTreeId.toLong() shl 35)
+  }
+}