Job interview task solved: day of week calculation

ImaginaryCalendarFinderInterface.php

<?php

interface ImaginaryCalendarFinderInterface
{
    /**
     * @param int $year
     * @param int $month
     * @param int $day
     * @return int
     */
    public function dayOfTheWeek($year, $month, $day);
}

ImaginaryCalendarInterface.php

<?php

interface ImaginaryCalendarInterface
{
    /**
     * Get the name of the $day.
     *
     * @return string
     */
    public function getDayName($day);

    /**
     * Get days of the week array.
     *
     * @return array
     */
    public function getDaysOfTheWeek();
    
    /**
     * Return is $year a leap year.
     * 
     * @param  int  $year
     * @return bool
     */
    public function isLeapYear($year);
    
    /**
     * Return number of days in the given $month.
     *
     * @param  int $month
     * @param  int $days
     * @return int Days in given $month due to leap year
    */
    public function getDaysInMonthOfLeapYear($month, $days);
    
    /**
     * Return months and number of days for each month as an array.
     * Example output:
     * [1] => 30, [2] => 27, [3] => 31, ...
     *
     * @return array
     */
    public function getMonthsAndDaysCount();
}

index.php

<?php

function __autoload($name)
{
    require __DIR__ . DIRECTORY_SEPARATOR . $name . '.php';
}

$calendar=new MyImaginaryCalendar();
$finder=new MyCalendarFinder($calendar);

$dayNumber=$finder->dayOfTheWeek(2013, 11, 17);

printf('Hooray, got %s', $calendar->getDayName($dayNumber));

MyCalendarFinder.php

<?php

class MyCalendarFinder implements ImaginaryCalendarFinderInterface
{
    /** @var ImaginaryCalendarInterface */
    protected $calendar;

    /** @param ImaginaryCalendarInterface $calendar */
    public function __construct(ImaginaryCalendarInterface $calendar)
    {
        $this->calendar=$calendar;
    }
    
    /**
     * @param int $year
     * @param int $month
     * @param int $day
     * @return int
     */
    public function dayOfTheWeek($year, $month, $day)
    {
        // get the blueprints
        $daysInWeek = $this->calendar->getDaysOfTheWeek();
        $months = $this->calendar->getMonthsAndDaysCount();
        
        // first current day is the first day of the week
        $currentDayOfTheWeek = array_keys($daysInWeek)[0];
        $firstDayOfTheWeek = $currentDayOfTheWeek;
        $lastDayOfTheWeek = array_keys($daysInWeek)[count($daysInWeek)-1];
        
        // go each year
        for ($iYear=0; $iYear <= $year; $iYear++) {

            // each month
            foreach ($months as $iMonth => $iMonthDays) {
            
                // if leap year modify day count
                if ($this->calendar->isLeapYear($iYear)) {
                    $iMonthDays=$this->calendar->getDaysInMonthOfLeapYear($iMonth, $iMonthDays);
                }
            
                // each day of the month
                for ($iDay=1; $iDay <= $iMonthDays; $iDay++) {
                
                    // if method is satisfied
                    if ($year == $iYear && $month == $iMonth && $day == $iDay) {
                        return $currentDayOfTheWeek;
                    }
                    
                    // move to the next day of the week
                    if ($currentDayOfTheWeek === $lastDayOfTheWeek) {
                        $currentDayOfTheWeek = $firstDayOfTheWeek;
                    } else {
                        ++$currentDayOfTheWeek;
                    }
                }
            }
        }
        
        throw new Exception('Loop seems invalid');
    }
}

MyImaginaryCalendar.php

<?php

class MyImaginaryCalendar implements ImaginaryCalendarInterface
{
    /**
     * @return string
     */
    public function getDayName($day)
    {
        return $this->getDaysOfTheWeek()[$day];
    }

    /**
     * @return array
     */
    public function getDaysOfTheWeek()
    {
        $dayIndexes=[1,2,3,4,5,6,7];
        $dayNames=['Monday','Tuesday','Wednesday','Thursday','Friday','Saturday','Sunday'];
        return array_combine($dayIndexes, $dayNames);
    }

    /**
     * @return bool
     */
    public function isLeapYear($year)
    {
        return $year % 5 == 0;
    }
    
    /**
     * @return int
     */
    public function getDaysInMonthOfLeapYear($month, $days)
    {
        if ($month == 13) {
            return $days - 1;
        }
        
        return $days;
    }
    
    /*
     * @return array
     */
    public function getMonthsAndDaysCount()
    {
        $months=[1,2,3,4,5,6,7,8,9,10,11,12,13];
        $days=[22,21,22,21,22,21,22,21,22,21,22,21,22];
        return array_combine($months, $days);
    }
}