Trigger on calculated date on Google AppMaker - google-apps-script

Question

I have function called alertnotice(to, message, body) that will be executed on a user onClick() event. The function will execute sendEmail(to, message, body) to send the email base on a calculated trigger as in variable triggerDay such as below:
function alertnotice(to, subject, body, dueDate, notifyBeforeDay) {//start of this class
function sendEmail(to, subject, body){
try {
MailApp.sendEmail({
to: to,
subject: subject,
htmlBody: body
});
} catch(e) {
console.error(JSON.stringify(e));
}
}
//check if there is an existing trigger for this process
var existingTrigger = PropertiesService.getScriptProperties().getProperty("sendEmailTrigger");
//set the renewal notice day
var triggerDay = (dueDate - notifyBeforeDay) / (1000*60*60*24);
//if the trigger already exists, inform user about it
if(existingTrigger) {
return "Alert notice had been sent";
} else { // if the trigger does not exists, continue to set the trigger to send alert notice
//runs the script every day at 1am on the time zone specified
var newTrigger = ScriptApp.newTrigger('sendEmail')
.timeBased()
.atTime(triggerDay)
.create();
var triggerId = newTrigger.getUniqueId();
if(triggerId) {
PropertiesService.getScriptProperties().setProperty("autoExportTrigger", triggerId);
return "Alert notice send successfully!";
} else {
return "Failed to send alert notice. Try again please";
}
}
}//end of this class
So for example, if the dueDate is 30/07/2018 and the notifyBeforeDay = 30, the function should send the email 30 days before the due date. I tried to achieve that but not so sure whether my algorithm will work. Can anyone give advice on this?

Answer 1

This implementation looks fragile to me. I would rather go with single trigger to avoid any possible duplicated emails and ensure at least one. Smth like this:
// I am server script, trigger me on schedule (for instance nightly)
function sendAlerts() {
var query = app.models.Customers.newQuery();
// query only for non-notified customers with upcoming due date
query.filters.NorificationAttempts._lessThan = ATTEMPTS_THRESHOLD;
query.filters.Notified._equals = false;
query.filters.DueDate._lessThan = <dueDate>;
var customers = query.run();
customers.forEach(function(customer) {
var success = sendNotification(customer);
if (success) {
customer.Notified = true;
} else {
customer.NorificationAttempts++;
}
// performance trade off in favor of consistency
app.saveRecords([customer]);
});
}
Trigger for such script can be installed by app's admin, you can find similar implementation in People Skills template.