Intersection of Days in PHP Array

Question

For a reservation system, I want to see if the start and end date of a user input intersect with the start and end date stored in two arrays. One array holds all the start dates and one all the end dates. The values from the arrays have been fetched from the database before.

$startArray = [0 => "1.1.2021", 1 => "5.1.2021", 2 => "10.1.2021"]; 
$endArray = [0 => "6.1.2021", 1 => "8.1.2021", 2 => "13.1.2021"];
$startUser = "3.1.2021";
$endUser = "5.1.2021";

My goal is the see if the selection the user has made intersects with the selection from the array. I have tried this

foreach ($startArray as $key => $value) {
            if (($startUser <= $endArray[$key]) && ($endUser >= $value)) {
                //action;
            }

That isn't working though. How would I best go about this?

EDIT: Date format is actually 2021-01-01. Both in the array as well as the user input.

Answer 1

It's hard comparing strings like that. What I like to do when checking dates, is to use DateTime objects which can be compared far more easily.

$d1 = new DateTime('2008-08-03 14:52:10');
$d2 = new DateTime('2008-01-03 11:11:10');
var_dump($d1 == $d2);
var_dump($d1 > $d2);
var_dump($d1 < $d2);
?>
bool(false)
bool(true)
bool(false)

Answer 2

The problem with your code is that you did not check that every date is between the 2 dates. Start date should be greater than start date and smaller than end date. End date should be greater than start date and smaller than end date

<?php
$startArray = [0 => "1.1.2021", 1 => "5.1.2021", 2 => "10.1.2021"];
$endArray = [0 => "6.1.2021", 1 => "8.1.2021", 2 => "13.1.2021"];
$startUser = DateTime::createFromFormat('d.m.Y', "3.1.2021");
$endUser =  DateTime::createFromFormat('d.m.Y', "5.1.2021");

if ($startUser->diff($endUser)->format("%R%d") <= 0){
    return false;
}
foreach ($startArray as $key => $value) {
    $start = DateTime::createFromFormat('d.m.Y', $value);
    $end = DateTime::createFromFormat('d.m.Y', $endArray[$key]);
    if ($startUser->diff($start)->format("%R%d") <= 0 && $startUser->diff($end)->format("%R%d") >=0 && $endUser->diff($start)->format("%R%d") <= 0 && $endUser->diff($end)->format("%R%d") >=0 ) {
        return true;
    }
}
return false;

For the sake of order and convenience of maintenance I would slightly change the structure of the data. I would build such an array

$dates = [['start' => "1.1.2021", 'end'= >"6.1.2021"] , ['start' => "5.1.2021", 'end'= >"8.1.2021"]

Answer 3

Your issue can be solved at the database level, with a single query. Let's assume the following simplified database setup:

• rooms table

number	price_class
1	Economy
2	Economy
3	Luxury
4	Luxury

• bookings table

room_number	start_date	end_date
1	2021-06-11	2021-06-15
2	2021-06-11	2021-06-15
3	2021-06-11	2021-06-15

Now let's also assume that the user searches for the term 2021-06-09 - 2021-06-12. That would mean the only unoccupied room for that period would be room 4. If we search for Economy rooms, there should be no results and if we search for Luxury, only room 4 should be in the result. The following query does it:

SELECT number FROM rooms
WHERE price_class = :priceClass AND number NOT IN (
  SELECT DISTINCT room_number FROM bookings b
  INNER JOIN rooms r ON r.number = b.room_number AND r.price_class = :priceClass
  WHERE start_date <= :userEndDate AND end_date >= :userStartDate
)

You can test it online in this fiddle.

How it works:

• The subquery selects all the rooms of given price class that have an overlap in the dates. The overlap logic is well explained in this post. We use distinct because one overlap is sufficient (theoretically, the user input can overlap with multiple intervals in the same room, but that doesn't matter - as soon as one overlaps, we know it's not available).
• Main query then selects all the rooms of given price class whose number was not found in the overlaps query (meaning they're available).

This will return all the rooms that are available. If you only need n rooms, just add LIMIT n to the main query. If you want to return random available rooms, you can add ORDER BY RAND() to the main query.