How to set up drip email system for PHP app - php

Question

My web app is using CakePHP 2.4 and I'm planning to build a "drip" email feature to deliver follow-up emails over time. This is a very common feature in modern websites, but I'm surprised by how little resources I'm able to find.
My question: Are there any established patterns for doing this? I have some ideas for how to do it but I don't want to reinvent the wheel.
(I did a quick search and I came up empty.)
Note: I'm aware of services like MailChimp which will do this, but my "drips" need to be done dynamically because they are linked to user actions which may or may not have already taken place. For example: I want to send an email every 3 days if a user has not completed their profile. Once they do, they should STOP getting the drips.

Answer 1

Right as requested.
Basically its more of a logic/workflow issue than anything else.
In your case you want to warn a user after 3 days and every 3 days thereafter that their profile isn't complete.
So first up you need some way of detecting that their profile isn't complete in this case I'll use a flag field IsComplete 0/1. By default its 0 (not complete). We also want to know a date that the user signed up so we'll use a simple mysql timestamp field populated with a mysql date in the format yyyy-mm-dd H:i:s, We also want to know a date the user was last email notified. For this we'll use another mysql field this time a datetime field in the same format yyyy-mm-dd H:i:s.
So our user db now looks something like this (note mysql syntax isn't correct)
IsComplete TINYINT 1 DEFAULT 0,
SignupDate TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
LastWarnDate DATETIME DEFAULT NULL
The NULL on the last warn date is important!
On your front end user profile edit/update page you'll simply add the following into the save bit
if (PSEUDO_CODE_ALL_FIELDS_ARE_COMPELTED==TRUE) {
"UPDATE tblusers SET IsComplete=1";
}
Now we have that bit out of the way lets look at the basic logic.
A drip mailer simply once a day needs to check your DB for pending actions and then send out notification emails as required. We can achieve this with a basic headless cron task running on the linux crond. You can find examples of running a php script via cron on google pretty much first response is exactly what you want. I'll not get into that but more into the actual cron script.
So now we know when the user signed up for your site, we know if their profile is complete and when we last warned them.
Our cronjob is nice and simple all it has to do is check is profile complete if not then check dates and send email.
$query = "SELECT EmailAddress,SignupDate,LastWarnDate FROM tblusers WHERE IsComplete=0"; //we don't need to bring back the completed users so for speed we look at uncomplete only
if (strlen($query->LastWarnDate) < 5) { // this is a little nasty but will work NULL is in the db field which returns 4 characters on strlen so a quick check that its < 5 means that we don't have a proper date in the field. There's better ways of doing this i'm being brief
// ok no last warn date so check sign up date vs now
if (DATE_DIFF($query->SignupDate,now()) >=3) {
//3 days or longer since signups so do first warn
"update tblusers SET LastWarnDate=NOW()";
mail(); //standard php mail function for sending email you can use swiftmail or another component if you like
} // its been less than 3 days so do nothing no need for an else
} else {
//we have a last warn date so check warn date vs now
if (DATE_DIFF($query->LastWarnDate,now()) >=3) {
//3 days or longer since last warn date so update last warn date to now and email
"update tblusers SET LastWarnDate=NOW()";
mail(); //standard php mail function for sending email you can use swiftmail or another component if you like
} //its been less than 3 days so do nothing no need for an else
}
So thats it very basic logic flow and example not valid php but you should be able to base your final solution on the code pretty easy.
Schedule the cron job to run at midnight every night and you're done.

Answer 2

As discussed with #Dave under his answer, I'm considering tracking the drips in a dedicated table in order to buy myself more flexibility...
Create a drips table with the following fields:
id (INT)
type (INT or ENUM) This maps to a specific type of drip with its corresponding conditions, etc
user_id (INT) foreign key linking to the user who will get the email
user_email* (VARCHAR) Optionally, the user's email address
count (INT) Tracks how many times it been sent for use in limiting the number of drips
last_sent (datetime) Tracks the date of the last time it was sent for use in maintaining the interval
When actions happen that potentially relate to drips, I check this table and add/delete scheduled drips accordingly. For example, when a user completes their profile, I would check this table and delete the corresponding drip. (<--This is a shortcoming of this approach, IMO.) I worry a bit about this part because some of the drips depend on various factors that may be difficult to keep track of throughout the code.
Every night, a cron job runs that loops through the drips and sends the emails that correspond to each type and which match the interval set in the code that corresponds to each. The job increments the count field and possibly also deletes records which have maxed out (maybe in query at the end of the job).