GASからIncomingWebhooks経由でSlackに時報を送るサンプル

TimeSignalToSlack.js

function isHoliday(date) {
  if (date.getDay() === 0 || date.getDay() === 6) {
    return true;
  }
  var calId = 'ja.japanese#holiday@group.v.calendar.google.com';
  var calendar = CalendarApp.getCalendarById(calId);
  var events = calendar.getEventsForDay(date);
  
  return events.length > 0;
}

function createNextHourTrigger(currentHour) {
  // 既存の時報トリガーをすべて削除する
  clearAllTimeSignalTriggers();
  
  var date = new Date();
  if (currentHour < 23) {
    // 現時刻が23時以前のときは次の時刻の時報トリガーを作成する
    var nextHour = currentHour　+　1;
    date.setHours(nextHour);
    date.setMinutes(0);
    date.setSeconds(0);
    ScriptApp.newTrigger("timeSignal").timeBased().at(date).create();
  } else {
    // 現時刻が23時以降の時は次の日の時報トリガーを作成する
    var nextDate = new Date();
    var count = 1;
    nextDate.setDate(date.getDate() + count);
    // 明日が休日なら明後日、明後日も休日なら明々後日...と休日でない日を次の時報開始日にする
    while (isHoliday(nextDate)) {
      count++;
      nextDate.setDate(date.getDate() + count);
    }
    nextDate.setHours(0);
    nextDate.setMinutes(0);
    nextDate.setSeconds(0);
    ScriptApp.newTrigger("timeSignal").timeBased().at(nextDate).create();
  }
}

function createNextTimeSignalNow() {
  var date = new Date();
  var time = date.toTimeString();
  var hour = parseInt(time.split(':')[0], 10);
  createNextHourTrigger(hour);
}

function clearAllTimeSignalTriggers() {
  var triggers = ScriptApp.getProjectTriggers()
  if (Array.isArray(triggers)) {
    triggers.forEach(function(trigger) {
      // timeSignalのトリガーのみを削除する
      if(trigger.getHandlerFunction() === 'timeSignal') {
        ScriptApp.deleteTrigger(trigger);
      }
    })
  }
}

function sendHttpPost(text){
  var url = '<ReplaceHereYourWebhookURL>'
  var json = {
    'text' : text
  };
  var payload = JSON.stringify(json)
  var options = {
    'method' : 'post',
    'contentType' : 'application/json',
    'payload' : payload
  };
   UrlFetchApp.fetch(url, options);
}

function timeSignal() {
  var date = new Date();
  var time = date.toTimeString();
  var hour = parseInt(time.split(':')[0], 10);
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = spreadsheet.getSheets()[0];
  var range = sheet.getRange(hour+1, 2);
  var value = range.getValue();
  if (value) {
    sendHttpPost(value);
    console.log("Time signal invoked at " + hour + ':00');
  }
  createNextHourTrigger(hour);
}