function main() {
  const scriptProperties = PropertiesService.getScriptProperties();
  const projects = JSON.parse(scriptProperties.getProperty('PROJECTS')); // 複数のprojectを指定可能
  const connect_sid = scriptProperties.getProperty('CONNECT_SID');
  let lastbackupedList = JSON.parse(scriptProperties.getProperty('LAST_BACKUPED_LIST') || '[]');

  const folder = DriveApp.getFolderById('xxx'); // お好みのfolderを選択してください
  lastbackupedList = projects.map((project, i) => downloadBackup({ project, connect_sid, folder, lastbackuped: lastbackupedList[i] || 0 }));

  scriptProperties.setProperty('LAST_BACKUPED_LIST', JSON.stringify(lastbackupedList));
}

const zero = n => String(n).padStart(2, '0');
function downloadBackup({ project, connect_sid, folder, lastbackuped }) {
  const backups = getBackupList({ project, connect_sid });
  const backupIds = backups
    .flatMap(({ backuped, id }) => backuped > lastbackuped ? [id] : [])
    .slice(0, 10); // 直近10ファイルまで取得する
  if (backupIds.length === 0) {
    console.log('no backup files found.');
    return lastbackuped;
  }
  const jsons = getBackupFiles({ project, connect_sid, fileIds: backupIds });
  console.log('Save backup files...');
  let saveNum = 0;
  jsons.forEach(json => {
    const exported = new Date(json.exported * 1000);

    const fileName = `${project}_${exported.getFullYear()}${zero(exported.getMonth() + 1)}${zero(exported.getDate())}${zero(exported.getHours())}${zero(exported.getMinutes())}${zero(exported.getSeconds())}.json`;
    folder.createFile(fileName, JSON.stringify(json, null, 2), 'application/json');
    saveNum++;
    console.log(`Saved: ${saveNum}/${jsons.length}`);
  });
  // backupの最終更新日時を返す
  const newLastBackuped = Math.max(...jsons.map(({ exported }) => parseInt(exported)));
  console.log(`Finish saving. Last backuped date: ${new Date(newLastBackuped * 1000)}`);

  return newLastBackuped;
}

function getBackupList({ project, connect_sid }) {
  console.log(`Start fetching the backup list of /${project}...`);
  const response = UrlFetchApp
    .fetch(`https://scrapbox.io/api/project-backup/${project}/list`, {
      headers: { Cookie: `connect.sid=${connect_sid}` },
    });
  const json = JSON.parse(response.getContentText());
  console.log(`Finish fetching.`, { backupNum: json.backups.length });
  return json.backups;
}

function getBackupFiles({ project, fileIds, connect_sid }) {
  console.log(`Start fetching ${fileIds.length} backups from /${project}...`, fileIds);
  const responses = UrlFetchApp
    .fetchAll(fileIds.map(fileId => {
      return {
        url: `https://scrapbox.io/api/project-backup/${project}/${fileId}.json`,
        headers: { Cookie: `connect.sid=${connect_sid}` },
      };
    })
    );
  const jsons = responses.map(response => JSON.parse(response.getContentText()));
  console.log('Finish fetching.');
  return jsons;
}