[Slack] ChatGPTをSlackで使えるようにする

const slackBotId = PropertiesService.getScriptProperties().getProperty('slackBotId');
const slackBotToken = PropertiesService.getScriptProperties().getProperty('slackBotToken');
const openAIApiKey = PropertiesService.getScriptProperties().getProperty('openAIApiKey');

function doPost(e, _IsTest = false) {
  const params = (_IsTest) ? JSON.parse(e) : JSON.parse(e.postData.getDataAsString());

  // Slackリクエスト検証
  if (params.type === 'url_verification') {
    return ContentService.createTextOutput(params.challenge);
  }

  const slackChannel = params.event.channel;
  const paramsText = params.event.text;

  // 無限ループ回避
  if ('subtype' in params.event) {
    return ContentService.createTextOutput('');
  }

  // @slackBotIdに反応してGPTからのレスをスレッドに返す
  if (paramsText.includes(`<@${slackBotId}>`) && params.event.user !== slackBotId) {
    // 3秒タイムアウトリトライ対策 (再送処理リクエストは200を返すだけ)
    let cache = CacheService.getScriptCache();
    if (cache.get(params.event.client_msg_id) == 'done') {
      return ContentService.createTextOutput();
    } else {
      cache.put(params.event.client_msg_id, 'done', 600);
    }

    let history;

    if (params.event.thread_ts) {
      history = getThreadHistory(slackChannel, params.event.thread_ts);
    } else {
      history = [{ role: 'user', content: paramsText }];
    }

    const message = requestToChatGPT(history);
    const new_message = replace_mention_with_username(message);
    sendMessagesToSlack(slackChannel, new_message, params.event.thread_ts || params.event.ts);
  }

  return ContentService.createTextOutput('');
}

function getThreadHistory(channel, thread_ts, max_history_len = 20) {
  const params = {
    'headers': {
      'Authorization': 'Bearer ' + slackBotToken
    }
  };

  const url = 'https://slack.com/api/conversations.replies?ts=' + thread_ts + '&channel=' + channel;
  const response = UrlFetchApp.fetch(url, params);

  const json = JSON.parse(response.getContentText('UTF-8'));
  if (json.ok) {
    const messages = json.messages;
    const results = [];
    for (let i = 0; i < messages.length; i++) {
      const message = messages[i];
      const role = message.user == slackBotId ? 'assistant' : 'user';
      results.push({ role: role, content: message.text });
      if (results.length >= max_history_len) {
        break;
      }
    }
    return results;
  } else {
    throw new Error('Failed to get thread: ' + json.error);
  }
}

function replace_mention_with_username(text) {
  const mentions = text.match(/<@\w+>/g);
  let replaced_text = text;
  if (mentions !== null) {
    for (let j = 0; j < mentions.length; j++) {
      const mention = mentions[j];
      const userId = mention.match(/<@(\w+)>/)[1];
      const username = getUserName(userId);
      if (username !== null) {
        const pattern = new RegExp(mention, "g");
        replaced_text = replaced_text.replace(pattern, `at:${username}`);
      }
    }
  }
  return replaced_text;
}

function getUserName(userId) {
  const url = "https://slack.com/api/users.info?user=" + userId;
  const params = {
    'headers': {
      'Authorization': 'Bearer ' + slackBotToken
    }
  };
  const response = JSON.parse(UrlFetchApp.fetch(url, params).getContentText('UTF-8'));
  Logger.log(response);
  if (response.ok) {
    return response.user.name;
  } else {
    return null;
  }
}

function sendMessagesToSlack(channel, message, thread_ts) {
  const url = "https://slack.com/api/chat.postMessage";
  var payload = {
    "token": slackBotToken,
    "channel": channel,
    "thread_ts": thread_ts,
    "text": message
  };
  params = {
    "method": 'post',
    'payload': payload
  }
  const response = UrlFetchApp.fetch(url, params);
  return response.ok;
}

function requestToChatGPT(history) {
  const apiUrl = 'https://api.openai.com/v1/chat/completions';
  const headers = {
    'Authorization': 'Bearer ' + openAIApiKey,
    'Content-type': 'application/json; charset=UTF-8'
  };
  const params = {
    'headers': headers,
    'method': 'POST',
    'muteHttpExceptions': true,
    'payload': JSON.stringify({
      'model': 'gpt-4o-mini',
      'messages': history,
      'temperature': 0.7,
    })
  };

  const response = JSON.parse(UrlFetchApp.fetch(apiUrl, params).getContentText('UTF-8'));
  return response.choices[0].message.content;
}