From 5015290dbeb29aac2a5f1cc3b25937661d9b458d Mon Sep 17 00:00:00 2001
From: Yiorgis Gozadinos <ggozadinos@gmail.com>
Date: Wed, 11 Jun 2025 09:54:49 +0200
Subject: [PATCH] fix(Chat Memory Manager Node): Fix simplifyMessages to not
 overwrite consecutive messages of same type (#16168)

---
 .../MemoryManager/MemoryManager.node.ts       |  42 +++++---
 .../test/MemoryManager.node.test.ts           | 102 ++++++++++++++++++
 2 files changed, 127 insertions(+), 17 deletions(-)
 create mode 100644 packages/@n8n/nodes-langchain/nodes/memory/MemoryManager/test/MemoryManager.node.test.ts

diff --git a/packages/@n8n/nodes-langchain/nodes/memory/MemoryManager/MemoryManager.node.ts b/packages/@n8n/nodes-langchain/nodes/memory/MemoryManager/MemoryManager.node.ts
index 6bfbe19779..efa5c76e5f 100644
--- a/packages/@n8n/nodes-langchain/nodes/memory/MemoryManager/MemoryManager.node.ts
+++ b/packages/@n8n/nodes-langchain/nodes/memory/MemoryManager/MemoryManager.node.ts
@@ -1,6 +1,7 @@
 /* eslint-disable n8n-nodes-base/node-dirname-against-convention */
 import type { BaseChatMemory } from '@langchain/community/memory/chat_memory';
-import { AIMessage, SystemMessage, HumanMessage, type BaseMessage } from '@langchain/core/messages';
+import type { MessageContent, BaseMessage } from '@langchain/core/messages';
+import { AIMessage, SystemMessage, HumanMessage } from '@langchain/core/messages';
 import { NodeConnectionTypes } from 'n8n-workflow';
 import type {
 	IDataObject,
@@ -17,24 +18,31 @@ interface MessageRecord {
 	hideFromUI: boolean;
 }
 
-function simplifyMessages(messages: BaseMessage[]) {
-	const chunkedMessages = [];
-	for (let i = 0; i < messages.length; i += 2) {
-		chunkedMessages.push([messages[i], messages[i + 1]]);
+export function simplifyMessages(messages: BaseMessage[]): Array<Record<string, MessageContent>> {
+	if (messages.length === 0) return [];
+
+	const result: Array<Record<string, MessageContent>> = [];
+	let index = 0;
+
+	while (index < messages.length) {
+		const currentGroup: Record<string, MessageContent> = {};
+
+		do {
+			const message = messages[index];
+			const messageType = message.getType();
+
+			if (messageType in currentGroup) {
+				break;
+			}
+
+			currentGroup[messageType] = message.content;
+			index++;
+		} while (index < messages.length);
+
+		result.push(currentGroup);
 	}
 
-	const transformedMessages = chunkedMessages.map((exchange) => {
-		const simplified = {
-			[exchange[0]._getType()]: exchange[0].content,
-		};
-
-		if (exchange[1]) {
-			simplified[exchange[1]._getType()] = exchange[1].content;
-		}
-
-		return simplified;
-	});
-	return transformedMessages;
+	return result;
 }
 
 const prepareOutputSetup = (ctx: IExecuteFunctions, version: number, memory: BaseChatMemory) => {
diff --git a/packages/@n8n/nodes-langchain/nodes/memory/MemoryManager/test/MemoryManager.node.test.ts b/packages/@n8n/nodes-langchain/nodes/memory/MemoryManager/test/MemoryManager.node.test.ts
new file mode 100644
index 0000000000..96d5e0c073
--- /dev/null
+++ b/packages/@n8n/nodes-langchain/nodes/memory/MemoryManager/test/MemoryManager.node.test.ts
@@ -0,0 +1,102 @@
+import { AIMessage, HumanMessage, SystemMessage } from '@langchain/core/messages';
+
+import { simplifyMessages } from '../MemoryManager.node';
+
+describe('simplifyMessages', () => {
+	it('should handle single message', () => {
+		const messages = [new HumanMessage('Hello')];
+		const result = simplifyMessages(messages);
+		expect(result).toEqual([{ human: 'Hello' }]);
+	});
+
+	it('should group different message types together', () => {
+		const messages = [
+			new HumanMessage('Hello, how are you?'),
+			new AIMessage("I'm doing well, thank you for asking! How about you?"),
+		];
+		const result = simplifyMessages(messages);
+		expect(result).toEqual([
+			{
+				human: 'Hello, how are you?',
+				ai: "I'm doing well, thank you for asking! How about you?",
+			},
+		]);
+	});
+
+	it('should separate consecutive messages of same type into different groups', () => {
+		const messages = [
+			new HumanMessage('First human message'),
+			new HumanMessage('Second human message'),
+			new AIMessage('AI response'),
+		];
+		const result = simplifyMessages(messages);
+		expect(result).toEqual([
+			{ human: 'First human message' },
+			{ human: 'Second human message', ai: 'AI response' },
+		]);
+	});
+
+	it('should handle three consecutive messages of same type', () => {
+		const messages = [new HumanMessage('1'), new HumanMessage('2'), new HumanMessage('3')];
+		const result = simplifyMessages(messages);
+		expect(result).toEqual([{ human: '1' }, { human: '2' }, { human: '3' }]);
+	});
+
+	it('should handle mixed message types with grouping', () => {
+		const messages = [
+			new SystemMessage('System message'),
+			new HumanMessage('Hello'),
+			new AIMessage('Hi there'),
+			new HumanMessage('Another human message'),
+			new AIMessage('Another AI message'),
+		];
+		const result = simplifyMessages(messages);
+		expect(result).toEqual([
+			{
+				system: 'System message',
+				human: 'Hello',
+				ai: 'Hi there',
+			},
+			{
+				human: 'Another human message',
+				ai: 'Another AI message',
+			},
+		]);
+	});
+
+	it('should handle system messages correctly', () => {
+		const messages = [
+			new SystemMessage('System instruction'),
+			new HumanMessage('User question'),
+			new AIMessage('AI response'),
+		];
+		const result = simplifyMessages(messages);
+		expect(result).toEqual([
+			{
+				system: 'System instruction',
+				human: 'User question',
+				ai: 'AI response',
+			},
+		]);
+	});
+
+	it('should handle alternating same types correctly', () => {
+		const messages = [
+			new HumanMessage('Human 1'),
+			new AIMessage('AI 1'),
+			new HumanMessage('Human 2'),
+			new AIMessage('AI 2'),
+		];
+		const result = simplifyMessages(messages);
+		expect(result).toEqual([
+			{
+				human: 'Human 1',
+				ai: 'AI 1',
+			},
+			{
+				human: 'Human 2',
+				ai: 'AI 2',
+			},
+		]);
+	});
+});