function main() {
  const now = (new Date()).getTime();
  const threads = settings.flatMap(({ channel, query }) => {
    const threads = GmailApp
      .search(query(now));
    console.log(`send ${threads.length} messages`);
    console.log(`query: ${query(now)}`);
    return threads.map(thread => {
      // 最新のメールだけ取得する
      const message = thread.getMessages().pop();
      send(message, channel);
      return thread;
    });
  });
  // 最後にまとめて既読にする
  threads.forEach(thread => thread.markRead());
}

function send(message, channel) {
  const body = {
    text: message.getSubject(),
    ...blocks(
      header(message.getSubject()),
      context(mrkdwn([
        `Date: ${message.getDate()}`,
        `From: ${message.getFrom()}`,
        `To: ${message.getTo()}`,
      ].join('\n'))),
      section(message.getPlainBody()),
    ),
  };
  try {
    UrlFetchApp.fetch(channel, {
      method: 'POST',
      contentType: 'application/json',
      payload: JSON.stringify(body),
      muteHttpExceptions: true,
    });
  } catch (e) {
    console.error(e);
  }
}