Increase days automatically in database - php

Question

I have an application where each user can request their vacations. There are two types of users, fixed and temporary. Fixed users have 24 days a year for vacations. The doubt comes with the temporary users.
Temporary users are added 2 days per month worked until December 31 of that year. For example:
user1 entered the company on 25/01/2019, until 31/12/2019 would have to increase it 2 days per month worked until that date, in total 22 days. As of 01/01/2020, those 2 days, will be increased every calendar month and start from 0, so that 01/01/2020 would have 0 days and 01/02/2020 would have 2 days.
Is there a PHP function or in MySQL a procedure for those 2 days to automatically add them to the database?
In the database I have a user table that has the following fields:
name available_days start_date
======= ================= ============
user1 0 25/01/2019
To those available_days is to which the days must be increased.
I have this function that calculates the difference in months since the user entered the company until today:
function difcurrentmonth($startdate){
$date = new DateTime($startdate);
$currentdate= (new DateTime)->format('Y-m-d H:i');
$finaldate = new DateTime($currentdate);
$dif = $date->diff($finaldate );
$month = ( $dif->y * 12 ) + $dif->m;
return $month;
}
$month = difcurrentmonth("2019-01-25");
$available_days= $month * 2;

Answer 1

Not quite an answer; too long for a comment...
-- Today is the 21st February 2019.
-- A temporary employee started work on 15th August 2018.
-- Accrued holiday resets on December 31st.
SELECT GREATEST('2018-08-15','2019-01-01') range_start
, '2019-02-21' range_end
, DATEDIFF('2019-02-21',GREATEST('2018-08-15','2019-01-01')) duration
, ROUND(DATEDIFF('2019-02-21',GREATEST('2018-08-15','2019-01-01'))/30,0) accrued;
+-------------+------------+----------+---------+
| range_start | range_end | duration | accrued |
+-------------+------------+----------+---------+
| 2019-01-01 | 2019-02-21 | 51 | 2 |
+-------------+------------+----------+---------+
In your scenario, '2018-08-15' would be replaced by a column from your database.

Answer 2

Firstly you will need to write a query that will get the available_days from the User table for user1.
I will assume you are using PDO for this example.
$stmt = $pdo_conn->prepare("UPDATE user SET available_days = available_days + 2 where [name] = :userName");
$stmt->bindParam(':userName', "user1");
$stmt->execute();
Create a cron job that runs on a certain day of the month. You might want to add the last_modified_date column to use as a safe catch to prevent updating the user multiple times within a given month.