From 71dee8a355e7f40ac2ad97ceada1cbc8608cee29 Mon Sep 17 00:00:00 2001
From: Wiktoria Walczak <wwalczak@google.com>
Date: Mon, 13 Jul 2026 03:15:57 -0700
Subject: [PATCH] refactor: extract shared compaction window helpers into
 CompactionUtils

PiperOrigin-RevId: 946920085
---
 .../adk/kt/summarizer/CompactionUtils.kt      | 47 +++++++++++++++++++
 .../summarizer/SlidingWindowEventCompactor.kt | 31 +-----------
 2 files changed, 48 insertions(+), 30 deletions(-)
 create mode 100644 core/src/commonMain/kotlin/com/google/adk/kt/summarizer/CompactionUtils.kt

diff --git a/core/src/commonMain/kotlin/com/google/adk/kt/summarizer/CompactionUtils.kt b/core/src/commonMain/kotlin/com/google/adk/kt/summarizer/CompactionUtils.kt
new file mode 100644
index 00000000..1d544330
--- /dev/null
+++ b/core/src/commonMain/kotlin/com/google/adk/kt/summarizer/CompactionUtils.kt
@@ -0,0 +1,47 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * 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.google.adk.kt.summarizer
+
+import com.google.adk.kt.events.Event
+
+/** Returns true when this event carries a context-compaction summary. */
+internal fun Event.isCompactionEvent(): Boolean = actions.compaction != null
+
+/**
+ * Returns the longest prefix of the given window that can be summarized without splitting a
+ * function-call/response pair or leaving a tool-confirmation (HITL) request unresolved.
+ *
+ * Performs a single left-to-right pass tracking "open" obligations keyed by call ID: a function
+ * call or a tool-confirmation request opens one, and a function response with the same ID closes
+ * it. The prefix is safe to summarize exactly at the points where no obligation is open, so the
+ * longest prefix ending at such a balanced point is returned (empty if the window never reaches a
+ * balanced point).
+ */
+internal fun longestSelfContainedPrefix(events: List<Event>): List<Event> {
+  val openIds = mutableSetOf<String>()
+  var safeLength = 0
+  for ((index, event) in events.withIndex()) {
+    for (response in event.functionResponses()) {
+      response.id?.let(openIds::remove)
+    }
+    for (call in event.functionCalls()) {
+      call.id?.let(openIds::add)
+    }
+    openIds.addAll(event.actions.requestedToolConfirmations.keys)
+    if (openIds.isEmpty()) safeLength = index + 1
+  }
+  return events.subList(0, safeLength)
+}
diff --git a/core/src/commonMain/kotlin/com/google/adk/kt/summarizer/SlidingWindowEventCompactor.kt b/core/src/commonMain/kotlin/com/google/adk/kt/summarizer/SlidingWindowEventCompactor.kt
index 7f20500f..e0621783 100644
--- a/core/src/commonMain/kotlin/com/google/adk/kt/summarizer/SlidingWindowEventCompactor.kt
+++ b/core/src/commonMain/kotlin/com/google/adk/kt/summarizer/SlidingWindowEventCompactor.kt
@@ -111,35 +111,6 @@ class SlidingWindowEventCompactor(private val config: EventsCompactionConfig) :
     }
 
     if (invocationsToCompact.size < compactionInterval) return null
-    return eventsToCompact.asReversed().longestSelfContainedPrefix().ifEmpty { null }
+    return longestSelfContainedPrefix(eventsToCompact.asReversed()).ifEmpty { null }
   }
 }
-
-private fun Event.isCompactionEvent(): Boolean = actions.compaction != null
-
-/**
- * Returns the longest prefix of the given window that can be summarized without splitting a
- * function-call/response pair or leaving a tool-confirmation (HITL) request unresolved.
- *
- * Performs a single left-to-right pass tracking "open" obligations keyed by call ID: a function
- * call or a tool-confirmation request opens one, and a function response with the same ID closes
- * it. The prefix is safe to summarize exactly at the points where no obligation is open, so the
- * longest prefix ending at such a balanced point is returned (empty if the window never reaches a
- * balanced point).
- */
-private fun List<Event>.longestSelfContainedPrefix(): List<Event> {
-  val openIds = mutableSetOf<String>()
-  var safeLength = 0
-  for ((index, event) in withIndex()) {
-    for (response in event.functionResponses()) {
-      response.id?.let(openIds::remove)
-    }
-    for (call in event.functionCalls()) {
-      call.id?.let(openIds::add)
-    }
-    openIds.addAll(event.actions.requestedToolConfirmations.keys)
-    // TODO(b/505630632): Add authentication requests handling.
-    if (openIds.isEmpty()) safeLength = index + 1
-  }
-  return subList(0, safeLength)
-}