shibanovp/route.ts

## route.ts
import { ChatOpenAI } from "langchain/chat_models/openai";
import { CallbackManager } from "langchain/callbacks";
import {
  ChatPromptTemplate,
  HumanMessagePromptTemplate,
  SystemMessagePromptTemplate,
  MessagesPlaceholder,
} from "langchain/prompts";

import { ConversationChain } from "langchain/chains";
import { BufferMemory, ChatMessageHistory } from "langchain/memory";
import {
  HumanChatMessage,
  AIChatMessage,
  BaseChatMessage,
} from "langchain/schema";

async function callChain(
  persona: string,
  input: string,
  pastMessages: BaseChatMessage[]
) {
  const encoder = new TextEncoder();
  const stream = new TransformStream();
  const writer = stream.writable.getWriter();
  const llm = new ChatOpenAI({
    temperature: 0.8,
    streaming: true,
    callbackManager: CallbackManager.fromHandlers({
      handleLLMNewToken: async (token) => {
        await writer.ready;
        await writer.write(encoder.encode(`${token}`));
      },
      handleLLMEnd: async () => {
        await writer.ready;
        await writer.close();
      },
      handleLLMError: async (e) => {
        await writer.ready;
        await writer.abort(e);
      },
    }),
  });

  const prompt = ChatPromptTemplate.fromPromptMessages([
    SystemMessagePromptTemplate.fromTemplate(persona),
    new MessagesPlaceholder("history"),
    HumanMessagePromptTemplate.fromTemplate("{input}"),
  ]);

  const memory = new BufferMemory({
    returnMessages: true,
    chatHistory: new ChatMessageHistory(pastMessages),
  });
  const chain = new ConversationChain({
    prompt,
    llm,
    memory,
  });
  chain.call({ input }).catch(console.error);
  return stream.readable;
}

export async function POST(request: Request) {
  const body = await request.json();
  const input: string = body.input;
  const persona: string = body.persona;
  const pastMessages: BaseChatMessage[] = body.pastMessages.map((msg: any) => {
    switch (msg.type) {
      case "ai":
        return new AIChatMessage(msg.text);
      case "human":
        return new HumanChatMessage(msg.text);
      default:
        throw new TypeError(`Unsupported message type: ${msg.type}`);
    }
  });
  try {
    const stream = callChain(persona, input, pastMessages);
    return new Response(await stream, {
      headers: {
        "Content-Type": "text/event-stream",
        Connection: "keep-alive",
        "Cache-Control": "no-cache, no-transform",
      },
    });
  } catch (err) {
    console.error(err);
    let error = "Unexpected message";
    if (err instanceof Error) {
      error = err.message;
    }
    return new Response(JSON.stringify({ error }), {
      status: 500,
      headers: {
        "Content-Type": "application/json",
      },
    });
  }
}
	import { ChatOpenAI } from "langchain/chat_models/openai";
	import { CallbackManager } from "langchain/callbacks";
	import {
	ChatPromptTemplate,
	HumanMessagePromptTemplate,
	SystemMessagePromptTemplate,
	MessagesPlaceholder,
	} from "langchain/prompts";

	import { ConversationChain } from "langchain/chains";
	import { BufferMemory, ChatMessageHistory } from "langchain/memory";
	import {
	HumanChatMessage,
	AIChatMessage,
	BaseChatMessage,
	} from "langchain/schema";

	async function callChain(
	persona: string,
	input: string,
	pastMessages: BaseChatMessage[]
	) {
	const encoder = new TextEncoder();
	const stream = new TransformStream();
	const writer = stream.writable.getWriter();
	const llm = new ChatOpenAI({
	temperature: 0.8,
	streaming: true,
	callbackManager: CallbackManager.fromHandlers({
	handleLLMNewToken: async (token) => {
	await writer.ready;
	await writer.write(encoder.encode(`${token}`));
	},
	handleLLMEnd: async () => {
	await writer.ready;
	await writer.close();
	},
	handleLLMError: async (e) => {
	await writer.ready;
	await writer.abort(e);
	},
	}),
	});

	const prompt = ChatPromptTemplate.fromPromptMessages([
	SystemMessagePromptTemplate.fromTemplate(persona),
	new MessagesPlaceholder("history"),
	HumanMessagePromptTemplate.fromTemplate("{input}"),
	]);

	const memory = new BufferMemory({
	returnMessages: true,
	chatHistory: new ChatMessageHistory(pastMessages),
	});
	const chain = new ConversationChain({
	prompt,
	llm,
	memory,
	});
	chain.call({ input }).catch(console.error);
	return stream.readable;
	}

	export async function POST(request: Request) {
	const body = await request.json();
	const input: string = body.input;
	const persona: string = body.persona;
	const pastMessages: BaseChatMessage[] = body.pastMessages.map((msg: any) => {
	switch (msg.type) {
	case "ai":
	return new AIChatMessage(msg.text);
	case "human":
	return new HumanChatMessage(msg.text);
	default:
	throw new TypeError(`Unsupported message type: ${msg.type}`);
	}
	});
	try {
	const stream = callChain(persona, input, pastMessages);
	return new Response(await stream, {
	headers: {
	"Content-Type": "text/event-stream",
	Connection: "keep-alive",
	"Cache-Control": "no-cache, no-transform",
	},
	});
	} catch (err) {
	console.error(err);
	let error = "Unexpected message";
	if (err instanceof Error) {
	error = err.message;
	}
	return new Response(JSON.stringify({ error }), {
	status: 500,
	headers: {
	"Content-Type": "application/json",
	},
	});
	}
	}
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