How to prevent overlapping time periods during validation? - php

Question

I have a membership that for any given day, can only have 3 users assigned to it.
user
start_date
end_date
User1
2023-01-01
2023-01-30
User2
2023-01-01
2023-01-25
User3
2023-01-26
2023-01-30
This set of records would be fine because on any given day there is not more than 3 users. My issue arises when I try to add:
user
start_date
end_date
User4
2023-01-01
2023-01-30
Using SELECT * FROM members WHERE start_date >= '2023-01-01' AND end_date <= '2023-01-30' returns 3 records like it should. I'm having a hard time trying to figure out how to make sure that none of these overlap to exceed 3.
I'm after advice on how I can achieve this using php, but pseudocode would work too

Answer 1

Loop over the date range in each result record, and count how many entries you got for any given date in an array. If you only need the maximum number of overlapping days, simply get the maximum of the array values. (If you need to know the specific dates where it would go over the limit - then you can loop the array.)
$rows = [
['2023-01-01', '2023-01-30'],
['2023-01-01', '2023-01-25'],
['2023-01-26', '2023-01-30'],
];
$countByDates = [];
foreach($rows as $row) { // this is going to be a classic while loop
// over your database result in your actual use case
$start = strtotime($row[0]); // access rather by column name than array index
$end = strtotime($row[1]);
do {
$date = date('Y-m-d', $start);
$countByDates[$date] = ($countByDates[$date] ?? 0) + 1;
$start = strtotime('+1 day', $start);
} while($start <= $end);
}
print_r($countByDates);
echo "maximum number of daily bookings: ", max($countByDates);
Result:
Array
(
[2023-01-01] => 2
[2023-01-02] => 2
[2023-01-03] => 2
[2023-01-04] => 2
[2023-01-05] => 2
[2023-01-06] => 2
[2023-01-07] => 2
[2023-01-08] => 2
[2023-01-09] => 2
[2023-01-10] => 2
[2023-01-11] => 2
[2023-01-12] => 2
[2023-01-13] => 2
[2023-01-14] => 2
[2023-01-15] => 2
[2023-01-16] => 2
[2023-01-17] => 2
[2023-01-18] => 2
[2023-01-19] => 2
[2023-01-20] => 2
[2023-01-21] => 2
[2023-01-22] => 2
[2023-01-23] => 2
[2023-01-24] => 2
[2023-01-25] => 1
[2023-01-26] => 2
[2023-01-27] => 2
[2023-01-28] => 2
[2023-01-29] => 2
[2023-01-30] => 2
)
maximum number of daily bookings: 2
https://3v4l.org/1W3WD