Business Time Challenge

addBusinessTime.js

function addBusinessTime(holiday, time, duration) {
    let finalTime = new Date(time.getTime());
    finalTime.setSeconds(finalTime.getSeconds() + duration);

    // First lets cover all possible cases when the start time is before the
    // holiday start.
    if (time.getTime() <= holiday.start.getTime()) {
        // If duration is negative or final time still before the holiday starts
        // then there is nothing to do, simply return the final time.
        if (duration <= 0 || (finalTime.getTime() <= holiday.start.getTime())) {
            return finalTime;
        }

        // Ok... final time is after the holiday starts, we have to calculate
        // the new final time by skipping the holiday.
        const extraTime = finalTime.getTime() - holiday.start.getTime();
        return new Date(holiday.end.getTime() + extraTime);
    }
    
    // This block covers all the possible cases where the start time is during
    // the holiday.
    if (time.getTime() >= holiday.start.getTime() && time.getTime() <= holiday.end.getTime()) {
        // When duration is positive the new start time is the holiday end,
        // otherwise, it is the holiday start, then we add the duration.
        finalTime = new Date(duration >= 0 ? holiday.end.getTime() : holiday.start.getTime());
        finalTime.setSeconds(finalTime.getSeconds() + duration);
        return finalTime;
    }
    
    // At this point we know the start time is after the holiday...

    // If duration is positive or the final time is after the holiday end we
    // can return the final time.
    if (duration >= 0 || (finalTime.getTime() >= holiday.end.getTime())) {
        return finalTime;
    }

    // Finally... we know start time is after the holiday and final time
    // is before or during the holiday, in this case we need to calculate
    // the final time by skipping the holiday.
    const difference = finalTime.getTime() - holiday.end.getTime();
    return new Date(holiday.start.getTime() + difference);
}