freeat.php

<?php

require_once 'vendor/autoload.php';

const FREE_TIME = 1;

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

function toPeriod($workingHours)
{
    $period = new stdClass();
    $period->from = timeToNumber($workingHours['from']);
    $period->to = timeToNumber($workingHours['to']);

    return $period;
}

function timeToNumber($time)
{
    return date('H', strtotime($time)) + date('i', strtotime($time)) / 60;
}

function freeAt($user, $newSession)
{
    $workingDays = collect([
        "Saturday", "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday",
    ])->combine($user['workHours']);

    $weekDay = date('l', strtotime($newSession['date']));
    $newSessionPeriod = toPeriod($newSession);
    $workingHours = $workingDays[$weekDay];

    if (empty($workingHours))
        throw new Exception("The user not working on {$weekDay}");

    $workingHoursPeriod = toPeriod($workingHours);

    if (!($newSessionPeriod->from >= $workingHoursPeriod->from
        && $newSessionPeriod->to <= $workingHoursPeriod->to)
    ) {
        throw new Exception("The user work only from {$workingHours['from']} to {$workingHours['to']}");
    }

    $conflictSession = collect($user['sessions'])
        ->where('date', $newSession['date'])
        ->where('status', "!=", "new")
        ->first(function ($approvedSession) use ($newSessionPeriod) {
            $approvedSessionPeriod = toPeriod($approvedSession);
            if ($newSessionPeriod->to + FREE_TIME <= $approvedSessionPeriod->from) {
            } elseif ($newSessionPeriod->from - FREE_TIME >= $approvedSessionPeriod->to) {
            } else {
                return true;
            }
        });

    if ($conflictSession)
        throw new Exception("This session conflict with a session from {$conflictSession['from']} to {$conflictSession['to']}");

    return true;
}

try {
    freeAt($user, ["date" => "17/6/2017", "from" => "12:00:00", "to" => "15:00:00"]);
    echo "Yahoo!";
} catch (Exception $e) {
    echo $e->getMessage();
}