FreeAt challenge solution using Intervals

freeat.php

<?php

use \Achse\Math\Interval\Utils\StringParser\IntegerIntervalStringParser as Parser;

require_once 'vendor/autoload.php';

const FREE_TIME = "01:00:00";

$user = [
    "workHours" => [
        ["from" => "08:00:00", "to" => "16:00:00"],
        [],
        ["from" => "08:00:00", "to" => "16:00:00"],
        [],
        ["from" => "08:00:00", "to" => "16:00:00"],
        [],
        ["from" => "08:00:00", "to" => "16:00:00"],
    ],
    "sessions"  => [
        [
            "date" => "6/17/2017", "status" => "approved",
            "from" => "09:00:00", "to" => "11:00:00",
        ],
        [
            "date" => "6/17/2017", "status" => "approved",
            "from" => "16:00:00", "to" => "18:00:00",
        ],
        [
            "date" => "6/17/2017", "status" => "new",
            "from" => "12:00:00", "to" => "14:00:00",
        ],
    ],
];

/**
 * Convert a from and to time strings to integer intervals
 * and add extra time before and after the interval if needed
 * @param $workingHours
 * @param string $extra
 * @return \Achse\Math\Interval\Intervals\IntegerInterval
 */
function toInterval($workingHours, $extra = "00:00:00")
{
    $from = timeToNumber(isset($workingHours['from']) ? $workingHours['from'] : 0) - timeToNumber($extra);
    $to = timeToNumber(isset($workingHours['to']) ? $workingHours['to'] : 0) + timeToNumber($extra);

    return Parser::parse("($from, $to)");
}

/**
 * Convert the time string to integer
 * e.g. 11:30 will be converted to 11.5 then 1150
 * @param $time
 * @return integer
 */
function timeToNumber($time)
{
    return (date('H', strtotime($time)) + date('i', strtotime($time)) / 60) * 100;
}

function freeAt($user, $newSession)
{
    $weekDay = date('l', strtotime($newSession['date']));
    $week = ["Saturday", "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday"];
    $workingHours = $user['workHours'][array_search($weekDay, $week)];

    $newSessionInterval = toInterval($newSession);

    if (toInterval($workingHours)->isContaining($newSessionInterval)) {
        return !(collect($user['sessions'])
            ->where('date', $newSession['date'])
            ->where('status', "approved")
            ->first(function ($approvedSession) use ($newSessionInterval) {
                return $newSessionInterval->getIntersection(toInterval($approvedSession, FREE_TIME));
            }));
    }

    return false;
}

$isFree = freeAt($user, ["date" => "6/17/2017", "from" => "11:00:00", "to" => "15:00:00"]);
var_dump($isFree);