Tutorial: Building a Chat Application

const getRequired = (name) => {
  const value = Deno.env.get(name);
  if (!value) {
    throw new Error(`Missing required environment variable: ${name}`);
  }
  return value;
};

const loadConfig = () => {
  return {
    apiUrl: getRequired("LLM_API_URL"),
    apiKey: getRequired("LLM_API_KEY"),
    model: getRequired("LLM_MODEL"),
    transcriptPath: Deno.env.get("TRANSCRIPT_PATH") ?? null,
  };
};

export { loadConfig };

const createInitialMessages = () => {
  return [
    {
      role: "system",
      content:
        "You are a concise assistant for software engineering questions. Keep answers short unless the user explicitly asks for more detail.",
    },
  ];
};

const addMessage = (messages, role, content) => {
  messages.push({ role, content });
};

export { addMessage, createInitialMessages };

const extractOutputText = (data) => {
  const messageItem = (data.output ?? []).find((item) => item.type === "message");
  const textPart = messageItem?.content?.find((part) =>
    part.type === "output_text"
  );
  return textPart?.text;
};

const requestCompletion = async ({ apiUrl, apiKey, model, messages }) => {
  const response = await fetch(apiUrl, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      "Authorization": `Bearer ${apiKey}`,
    },
    body: JSON.stringify({
      model,
      input: messages,
    }),
  });

  if (!response.ok) {
    throw new Error(`LLM request failed with status ${response.status}`);
  }

  const data = await response.json();
  const content = extractOutputText(data);

  if (typeof content !== "string" || content.trim().length === 0) {
    throw new Error("LLM response did not contain usable text content.");
  }

  return content;
};

export { extractOutputText, requestCompletion };

const saveTranscript = async (messages, filepath) => {
  const text = JSON.stringify(messages, null, 2);
  await Deno.writeTextFile(filepath, text);
};

export { saveTranscript };

import { addMessage, createInitialMessages } from "./src/chatSession.js";
import { loadConfig } from "./src/config.js";
import { requestCompletion } from "./src/llmClient.js";
import { saveTranscript } from "./src/transcript.js";

const config = loadConfig();
const messages = createInitialMessages();

console.log("CLI chat started. Type 'exit' to quit.");

while (true) {
  const input = prompt("> ");

  if (input === null || input.trim().toLowerCase() === "exit") {
    break;
  }

  if (input.trim().length === 0) {
    continue;
  }

  addMessage(messages, "user", input);

  try {
    const reply = await requestCompletion({
      apiUrl: config.apiUrl,
      apiKey: config.apiKey,
      model: config.model,
      messages,
    });

    addMessage(messages, "assistant", reply);
    console.log(`\n${reply}\n`);

    if (config.transcriptPath) {
      await saveTranscript(messages, config.transcriptPath);
    }
  } catch (error) {
    console.error(`Error: ${error.message}`);
  }
}