const CLOUD_SHEET = 'Cloud';
const BACKUP_SHEET = 'Backups';
const MAX_BACKUPS = 50;
const MIN_DATA_LENGTH = 80;

function getSheet(name, header) {
  const ss = SpreadsheetApp.getActiveSpreadsheet();
  let sheet = ss.getSheetByName(name);
  if (!sheet) sheet = ss.insertSheet(name);
  if (sheet.getLastRow() === 0) sheet.appendRow(header);
  return sheet;
}

function getCloudSheet() {
  return getSheet(CLOUD_SHEET, ['key', 'data', 'timestamp']);
}

function getBackupSheet() {
  return getSheet(BACKUP_SHEET, ['backup_at', 'data', 'timestamp']);
}

function jsonResponse(payload) {
  return ContentService
    .createTextOutput(JSON.stringify(payload))
    .setMimeType(ContentService.MimeType.JSON);
}

function backupCurrentCloud() {
  const cloud = getCloudSheet();
  if (cloud.getLastRow() < 2) return;

  const row = cloud.getRange(2, 1, 1, 3).getValues()[0];
  const currentData = row[1] || '';
  if (!currentData) return;

  const backups = getBackupSheet();
  backups.insertRowBefore(2);
  backups.getRange(2, 1, 1, 3).setValues([[
    new Date(),
    currentData,
    row[2] || Date.now()
  ]]);

  const extraRows = backups.getLastRow() - 1 - MAX_BACKUPS;
  if (extraRows > 0) {
    backups.deleteRows(MAX_BACKUPS + 2, extraRows);
  }
}

function doGet() {
  const sheet = getCloudSheet();
  const data = sheet.getRange(2, 2).getValue() || '';
  const timestamp = Number(sheet.getRange(2, 3).getValue() || 0);
  return jsonResponse({ success: true, data, timestamp });
}

function doPost(e) {
  try {
    const body = JSON.parse((e.postData && e.postData.contents) || '{}');
    if (!body.data) throw new Error('Missing data');
    if (String(body.data).length < MIN_DATA_LENGTH) {
      throw new Error('Refuse short payload to avoid overwriting backup with empty data');
    }

    const sheet = getCloudSheet();
    if (sheet.getLastRow() < 2) sheet.appendRow(['cloud', '', '']);

    backupCurrentCloud();

    sheet.getRange(2, 1, 1, 3).setValues([[
      'cloud',
      body.data,
      body.timestamp || Date.now()
    ]]);

    return jsonResponse({ success: true });
  } catch (error) {
    return jsonResponse({ success: false, error: error.message });
  }
}