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LangchainChatLlm.ts
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LangchainChatLlm.ts
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import {
BaseChatModel,
BaseChatModelCallOptions,
} from "@langchain/core/language_models/chat_models";
import {
BaseMessagePromptTemplateLike,
ChatPromptTemplate,
} from "@langchain/core/prompts";
import { ChatLlm, OpenAiChatMessage } from "./ChatLlm";
import { AssistantMessage } from "./ConversationsService";
export interface MakeLangchainChatLlmProps {
chatModel: BaseChatModel;
callOptions?: BaseChatModelCallOptions;
}
/**
Use any Langchain JS [`ChatModel`](https://js.langchain.com/docs/modules/model_io/chat/)
to talk to an LLM.
Note: This ChatLLM does not currently support tool calling.
*/
export function makeLangchainChatLlm({
chatModel,
callOptions,
}: MakeLangchainChatLlmProps): ChatLlm {
return {
async answerQuestionAwaited({ messages }) {
const prompts = ChatPromptTemplate.fromMessages(
messages.map((m) => messageBaseMessagePromptTemplateLike(m))
);
const chain = prompts.pipe(chatModel);
const res = await chain.invoke({}, callOptions);
return {
role: "assistant",
content: typeof res.content === "string" ? res.content : "",
} satisfies AssistantMessage;
},
answerQuestionStream: async ({ messages }) =>
(async function* () {
const prompts = ChatPromptTemplate.fromMessages(
messages.map((m) => messageBaseMessagePromptTemplateLike(m))
);
const chain = prompts.pipe(chatModel);
const stream = await chain.stream({}, callOptions);
let index = 0;
for await (const chunk of stream) {
index++;
yield {
id: index.toString(),
created: new Date(),
choices: [
{
finishReason: null,
index: index,
delta: {
role: "assistant",
content:
typeof chunk.content === "string" ? chunk.content : "",
toolCalls: [],
},
},
],
promptFilterResults: [],
};
}
})(),
};
}
function messageBaseMessagePromptTemplateLike(
message: OpenAiChatMessage
): BaseMessagePromptTemplateLike {
return [message.role, message.content ?? ""];
}