PHP: Algorithm for finding available appointment times to choose from - php

Question

A practice needs to schedule an appointment with a patient and assign that appointment to a doctor.
An appointment comprises of various tests, and a start time.
A test comprises of a name and a duration.
As such, we can calculate required duration by summing the duration of all required tests.
The practice can select a date, doctor, and the required tests - using ajax, I want to be able to return a json object of available time slots for the patient to choose from.
Build an array of all available times (20 minute intervals between open and close).
-
$practiceOpen = strtotime($input['date'] . ' 10:00');
$practiceClose = strtotime($input['date'] . ' 18:00');
$interval = 20 * 60; // 20 mins
while ($start < ( $end - $requiredDuration * 60 ) )
{
$times[] = date( "Y-m-d H:i", $start);
$start += $interval;
}
Get a collection of all appointments on specified date for that doctor.
nested foreach with appointments[] (2) and times[] (1) to remove all unavailable times from the master times[].
example
foreach ($appointments as $appointment)
{
foreach($times as $key => $time)
{
$time = strtotime($time);
if (
$time + $requiredDuration * 60 >= strtotime($appointment->appointment)
&&
$time < strtotime($appointment->appointment) + $appointment->duration * 60
) { unset($times[$key]); }
}
}
The if statement basically says
**If**
start time plus the required duration of the tests is larger than the start time of the existing appointment **AND**
start time is less than existing appointment + duration of existing appointment
**Then** Remove that timeslot from array.
The question: The above snippet / algorithm appears to work, however what is wanted was a pointer in the right direction for:
Is this the proper / most efficient way of tackling the problem?
Are there known algorithms which handle this which I could implement which would work better or faster than my implementation?
Is there a way to test this properly to see if I am not excluding appointment times which should be available or including times which are not available?

Answer 1

To those looking for a algorithm to find all the times available for the day, taking into consideration the already unavailable times, here's what I have done:
First decide what is the range of time you are accepting bookings (ex.: from 08:00am to 08:00pm)
Avoid multiple database query. Instead of checking database for each time we are looping, get all the unavailable slots into an array (single query only)
Decide what is the amount of minutes every session/booking takes
Decide what is the gap between times selection (mine is usually 5 minutes)
Full code:
$start = strtotime('08:00');
$end = strtotime('20:00');
$minutesPerSession = 30;
$minutesPerGap = 5;
$verifyDay = date('Y-m-d'); // set the day to check
// query database here and grab all the unavailables into an array
$unavailables =
[
['start_at' => '2021-12-27 09:00', 'end_at' => '2021-12-27 09:30'],
['start_at' => '2021-12-27 10:20', 'end_at' => '2021-12-27 10:50'],
['start_at' => '2021-12-27 11:00', 'end_at' => '2021-12-27 11:30'],
];
$slotsAvailable = [];
for ($i = $start; $i <= $end; $i = $i + $minutesPerGap * 60)
{
$time = date('H:i', $i);
$range = date('H:i', strtotime("{$minutesPerSession} minutes", $i));
$dateStart = $verifyDay . ' ' . $time;
$dateEnd = $verifyDay . ' ' . $range;
$isAvailable = true;
foreach ($unavailables as $key => $unavailable)
{
if
(
($unavailable['start_at'] <= $dateStart && $unavailable['end_at'] >= $dateStart) ||
($unavailable['start_at'] <= $dateEnd && $unavailable['end_at'] >= $dateEnd) ||
($unavailable['start_at'] >= $dateStart && $unavailable['end_at'] <= $dateEnd)
)
{
$isAvailable = false;
break;
}
}
if ($isAvailable)
array_push($slotsAvailable, $time);
}
print_r($slotsAvailable);
In my case, this would give me available slots like:
[0] => 08:00
[1] => 08:05
[2] => 08:10
[3] => 08:15
[4] => 08:20
[5] => 08:25
[6] => 09:35
[7] => 09:40
[8] => 09:45
[9] => 11:35
[....]