I wrote this 5 years ago, I think it's for determining available times for booking car wash, but I have no idea how it works

Booking.php

<?php
public function get_available_times($serv, $date = false)
    {
        $CI = &get_instance();

        $opening = 9 * 60;
        $closing = 19 * 60;

        $available = array();

        if ($date === false) {
            $date = date('Y-m-d');
        }

        $service = $CI->db->get_where('services', array('id' => $serv))->result();
        if ($service === false) {
            return false;
        }
        $service = $service[0];

        $orders = $CI->db->where('date', $date)->where('status !=', 'deactivated')->order_by('time', 'asc')->get('booking')->result();

        $open = $opening;

        foreach ($orders as $n => $order) {
            if ($n > 0) {
                $open = $orders[$n - 1]->end;
            }
            if ($n === count($orders)) {
                $start = $closing;
            } else {
                $start = $order->time;
            }

            $div = floor(($start - $open) / $service->duration);
            if ($div >= 1) {
                for ($i = 1; $i <= $div; ++$i) {
                    $available[] = $open + ($service->duration * ($i - 1));
                }
            }
            $open = $order->end;
        }

        $div = ($closing - $open) / $service->duration;
        if ($div >= 1) {
            for ($i = 1; $i <= $div; ++$i) {
                $available[] = $open + ($service->duration * ($i - 1));
            }
        }

        return $available;
    }