Work out business days - ignoring holidays

BusinessDayCalculator.php

<?php

use Carbon\Carbon;

/**
 *  BusinessDayCalculator
 *  Computes date interval, or adds days to a date while
 *  skipping the weekend.
 *
 *  NOT considered:
 *  - Holidays
 *  - Locales where Saturday and Sunday are not the weekend.
 */

class BusinessDayCalculator
{
    // See https://gist.github.com/quawn/8503445
    static public function countBusinessDays( $start, $end)
    {
        if (is_string($start)) {
            $start = new Carbon($start);
        }
        if (is_string($end)) {
            $end = new Carbon($end);
        }

        $actualDays = $start ->diff($end)->d; // "Day" component of interval

        $fullWeeks = floor( $actualDays / 7 );
        $remainingDays = fmod( $actualDays, 7);

        $startingDay = $start->dayOfWeekIso;
        $endingDay = $end->dayOfWeekIso;

        /**
         * The two can be equal in leap years when february has 29 days,
         * In the first case the whole interval is within a week,
         * in the second case the interval is two or more weeks.
         */
        if ($startingDay <= $endingDay) {
            if ($startingDay <= 6 && 6 <= $endingDay) $remainingDays--;
            if ($startingDay <= 7 && 7 <= $endingDay) $remainingDays--;
        }
        else {
            /**
             * the day of the week for start is later than the day of
             * the week for end
             */
            if ($startingDay == 7) {
                /**
                 * if the start date is a Sunday,
                 * then we definitely subtract 1 day
                 */
                $remainingDays--;

                if ($endingDay == 6) {
                    /**
                     * if the end date is a Saturday,
                     * then we subtract another day
                     */
                    $remainingDays--;
                }
            }
            else {
                /**
                 * the start date was a Saturday (or earlier),
                 * and the end date was (Mon..Fri)
                 * so we skip an entire weekend and subtract 2 days
                 */
                $remainingDays -= 2;
            }
        }

        /**
         * The no. of business days is:
         * (no. of weeks between the dates) * (5 working days) + the remainder
         * february in non leap years will give a remainder of 0
         */
        $workingDays = $fullWeeks * 5;
        if ($remainingDays > 0 )
        {
            $workingDays += $remainingDays;
        }

        return $workingDays;

    }

    static public function addBusinessDays($date, int $businessDays )
    {
        if (is_string($date)) {
            $date = new Carbon($date);
        }

        $weeks = floor($businessDays / 5);
        $remainder = fmod( $businessDays, 5);

        /** if the date is in the weekend, skip to Monday, before adding days */
        if ($date->dayOfWeekIso == 6) $date->addDays(2);
        if ($date->dayOfWeekIso == 7) $date->addDay();

        $date->addWeeks($weeks);

        /**
         * does the current day plus remainder take us
         * into/through the weekend?
         */
        if ($date->dayOfWeekIso + $remainder > 6) {
            /** skip over Saturday and Sunday */
            $remainder += 2;
        }

        $date->addDays($remainder);

        return $date;
    }

    static public function subtractBusinessDays($date, int $businessDays )
    {
        if (is_string($date)) {
            $date = new Carbon($date);
        }

        $weeks = floor($businessDays / 5);
        $remainder = fmod( $businessDays, 5);

        /** if the date is in the weekend, skip back to Friday, before subtracting days */
        if ($date->dayOfWeekIso == 6) $date->subDay();
        if ($date->dayOfWeekIso == 7) $date->subDays(2);

        $date->subWeeks($weeks);

        /**
         * does the current day minus remainder take us
         * into/through the previous weekend?
         */
        if ($date->dayOfWeekIso - $remainder < 1) {
            /** skip over Saturday and Sunday */
            $remainder += 2;
        }

        $date->subDays($remainder);

        return $date;
    }
}