Frost alert on your phone the evening before a cold night

1// Frost alert: checks the overnight forecast each evening and tells your phone2// through ntfy when it's going to be cold enough for frost. Uses the free Open-Meteo forecast.3 4let CONFIG = {5  latitude: -37.81,6  longitude: 144.96,7  checkAt: "17:00",8  frostTemp: 2,9  ntfyTopic: "",10};11 12// Check the clock every 20 seconds, so the check runs within the minute set.13let CHECK_EVERY_SEC = 20;14// If the forecast doesn't come back, ask once more ten minutes later.15let RETRY_SEC = 600;16 17let lastCheckDate = -1;18let retried = false;19 20// Local date (days since 1970) and "HH:MM", or null before the clock has synced.21function localNow() {22  let s = Shelly.getComponentStatus("sys");23  if (s === null || typeof s.unixtime !== "number" || s.time === null) return null;24  return { date: Math.floor((s.unixtime + (s.utc_offset || 0)) / 86400), time: s.time };25}26 27// Today's and tomorrow's lows. The coldest part of tonight is early tomorrow28// morning, so the second day's low is the one that matters.29function forecastUrl() {30  return "https://api.open-meteo.com/v1/forecast?latitude=" + CONFIG.latitude +31    "&longitude=" + CONFIG.longitude +32    "&daily=temperature_2m_min&timezone=auto&forecast_days=2";33}34 35function onSent(res, err) {36  if (err !== 0 || res.code !== 200) print("Couldn't send the alert to ntfy.");37}38 39function alert(msg) {40  print(msg);41  if (CONFIG.ntfyTopic === "") return;42  Shelly.call("HTTP.Request", {43    method: "POST",44    url: "https://ntfy.sh/" + CONFIG.ntfyTopic,45    body: msg,46    headers: { "Content-Type": "text/plain" },47    timeout: 15,48  }, onSent);49}50 51function noForecast(why) {52  if (!retried) {53    retried = true;54    print("Couldn't get the forecast (" + why + "). Trying again in 10 min.");55    Timer.set(RETRY_SEC * 1000, false, fetchForecast);56    return;57  }58  print("Still no forecast (" + why + "). No frost check tonight.");59}60 61function onForecast(res, err) {62  if (err !== 0 || res.code !== 200) return noForecast("error " + (err !== 0 ? err : res.code));63  let low = null;64  try {65    low = JSON.parse(res.body).daily.temperature_2m_min[1];66  } catch (e) {67    return noForecast("unreadable reply");68  }69  if (typeof low !== "number") return noForecast("no temperature in the reply");70  if (low <= CONFIG.frostTemp) {71    alert("Frost likely tonight: the forecast low is " + low + " C. Cover or bring in anything tender.");72  } else {73    print("Forecast low of " + low + " C tonight. No frost alert.");74  }75}76 77function fetchForecast() {78  Shelly.call("HTTP.GET", { url: forecastUrl(), timeout: 15 }, onForecast);79}80 81function check() {82  let now = localNow();83  // Without the clock it can't tell the time, so it does nothing.84  if (now === null) return;85  if (now.time !== CONFIG.checkAt || now.date === lastCheckDate) return;86  lastCheckDate = now.date;87  retried = false;88  fetchForecast();89}90 91Timer.set(CHECK_EVERY_SEC * 1000, true, check);92print("Frost alert started. Checks the forecast at " + CONFIG.checkAt + " each day, alerts at " +93  CONFIG.frostTemp + " C or below.");