Spend anomaly alert

// Spend anomaly alert
// Compares yesterday's cost per campaign against the same weekday over the
// previous four weeks, so weekend and weekday patterns do not raise false alarms.
// FROM campaign covers every channel type, including Performance Max and Demand Gen.
// Read-only: it alerts, it does not pause anything.

var THRESHOLD = 0.4;   // 0.4 = alert at 40% above or below the baseline
var MIN_COST  = 10;    // skip campaigns too small to matter
var EMAIL     = '';    // leave empty to log only

function main() {
  var tz = AdsApp.currentAccount().getTimeZone();

  var yesterday = daysAgo(1, tz);
  var baseline  = [daysAgo(8, tz), daysAgo(15, tz), daysAgo(22, tz), daysAgo(29, tz)];

  var today = costByCampaign(yesterday, yesterday);
  var past  = {};

  for (var i = 0; i < baseline.length; i++) {
    var day = costByCampaign(baseline[i], baseline[i]);
    for (var n1 in day) {
      if (!past[n1]) { past[n1] = []; }
      past[n1].push(day[n1]);
    }
  }

  var alerts = [];
  for (var name in today) {
    var samples = past[name] || [];
    if (samples.length < 2) { continue; }   // too new to have a baseline

    var avg = 0;
    for (var j = 0; j < samples.length; j++) { avg += samples[j]; }
    avg = avg / samples.length;

    if (avg === 0) { continue; }
    if (avg < MIN_COST && today[name] < MIN_COST) { continue; }

    var delta = (today[name] - avg) / avg;
    if (Math.abs(delta) >= THRESHOLD) {
      alerts.push([name, today[name], avg, delta]);
    }
  }

  if (alerts.length === 0) {
    Logger.log('No campaign moved more than ' + (THRESHOLD * 100) + '% on ' + yesterday + '.');
    return;
  }

  alerts.sort(function (a, b) { return Math.abs(b[3]) - Math.abs(a[3]); });

  var lines = ['campaign\tyesterday\tbaseline\tchange'];
  for (var k = 0; k < alerts.length; k++) {
    var a = alerts[k];
    lines.push(a[0] + '\t' + a[1].toFixed(2) + '\t' + a[2].toFixed(2) + '\t' +
               (a[3] > 0 ? '+' : '') + (a[3] * 100).toFixed(0) + '%');
  }

  var body = AdsApp.currentAccount().getName() + '\n' +
             'Spend on ' + yesterday + ' against the same weekday, previous four weeks.\n\n' +
             lines.join('\n');

  Logger.log(body);
  if (EMAIL) {
    MailApp.sendEmail(EMAIL, 'Spend anomaly - ' + AdsApp.currentAccount().getName(), body);
  }
}

function costByCampaign(from, to) {
  var out  = {};
  var rows = AdsApp.search(
    'SELECT campaign.name, metrics.cost_micros ' +
    'FROM campaign ' +
    'WHERE segments.date BETWEEN "' + from + '" AND "' + to + '" ' +
    '  AND campaign.status != "REMOVED"'
  );
  while (rows.hasNext()) {
    var r = rows.next();
    out[String(r.campaign.name)] = Number(r.metrics.costMicros) / 1000000;
  }
  return out;
}

function daysAgo(n, tz) {
  var d = new Date();
  d.setDate(d.getDate() - n);
  return Utilities.formatDate(d, tz, 'yyyy-MM-dd');
}