Cron jobs - how to prevent sending a repeated notification? - php

Question

I am trying to send a notification when a certain event is about to happen in one hour.
For testing purposes I currently am having the cron process run once a minute. But I suspect there is a more efficient way to go about this.
I am trying to avoid keeping track of notifications, and so I am trying to just build in some logic so that I can get one trigger on the notification.
Here is my current process:
function webinar_starts_onehour() {
// Get all lessons that are in future
$today = time();
$args = array(
'post_type' => 'lessons',
'post_status' => 'publish',
'posts_per_page' => -1,
'meta_query' => array(
'key' => 'webinar_time',
'value' => $today,
'compare' => '>='
)
);
$lessons = get_posts( $args );
$notifications = get_notifications( 'webinar_starts_onehour' );
// Foreach lesson
foreach ( $lessons as $lesson ) {
$webinar_time = strtotime($lesson->webinar_time);
$difference = round(($webinar_time - $today) / 3600,2);
if (($difference > .98) && ($difference < 1.017)) {
// do something
}
}
}
So what I am trying to do is have it trigger if it is a little less than an hour away or a little more (that is +- one minute).
I suspect my condition can be set twice in some situations and so trying to figure out a more solid way to make sure with a cron that fires every minute, that this condition would be triggered only once.
Ideas?
And if you think this is really unreliable (which I know it is) what would be a pragmatic way to add a table to track this sort of notification? Would I just create a table, say, sent_notifications which would have user_id, notification_id, lesson_id, status
and then check if there was a successful notification for this particular lesson and for failed sends use another cron to continuously try sending the failed ones?
thanks,
Brian