time_calculator.py

def get_days_later(days):
    """ Format the days later into string"""
    if days == 1:
        return "(next day)"
    elif days > 1:
        return f"({days} days later)"
    return ""


def add_time(start_time, end_time, day=False):
    
    # constants
    HOURS_IN_ONE_DAY = 24
    HOURS_IN_HALF_DAY = 12
    WEEK_DAYS = [
        "monday",
        "tuesday",
        "wednesday",
        "thursday",
        "friday",
        "saturday",
        "sunday",
    ]


    days_later = 0
    hours, mins = start_time.split(":")
    mins, period = mins.split(" ")
    end_time_hrs, end_time_mins = end_time.split(":")

    # Clean time data
    hours = int(hours)  # start time  hours
    mins = int(mins)  # start time  minutes
    end_time_hrs = int(end_time_hrs)  # end time hours
    end_time_mins = int(end_time_mins)  # end time minutes
    period = period.strip().lower()  # AM or PM

    # Combine start time and end time hrs and minutes
    total_mins = mins + end_time_mins
    total_hours = hours + end_time_hrs

    # Shift minutes to hour if minutes is over 60
    if total_mins >= 60:
        total_hours += int(total_mins / 60)
        total_mins = int(total_mins % 60)

    if end_time_hrs or end_time_mins:
        # If `PM`, flip period to `AM` if hours over 12
        if period == "pm" and total_hours > HOURS_IN_HALF_DAY:
            # if hours over 24hr then add  days
            if total_hours % HOURS_IN_ONE_DAY >= 1.0:
                days_later += 1

        if total_hours >= HOURS_IN_HALF_DAY:
            hours_left = total_hours / HOURS_IN_ONE_DAY
            days_later += int(hours_left)

            # e.g: 54hr / 24 = 2.25 days <-- append 2 days
            # e.g.: 36hr / 24 = 1.5 days <-- append 1 days

        temp_hours = total_hours
        while True:
            # Constantly reverse period until
            # total_hours are less than half a day
            if temp_hours < HOURS_IN_HALF_DAY:
                break
            if period == "am":
                period = "pm"
            else:
                period = "am"
            temp_hours -= HOURS_IN_HALF_DAY

    """
    Recalculate Hours and Minutes 
    
     Since we have already taken care of the days,
     we now need to calculate the hours remaining.
     This can be done by subtracting the remaining days(in hours) 
     from the total hours remaining 
        
        e.g. hrs % oneday -->  55hrs % 24 = 7 ---> 7 hours remaining
    """
    remaining_hours = int(total_hours % HOURS_IN_HALF_DAY) or hours + 1
    remaining_mins = int(total_mins % 60)

    # Format the results
    results = f"{remaining_hours}:{remaining_mins:02} {period.upper()}"
    if day:  # add the day of the week
        day = day.strip().lower()
        selected_day = int((WEEK_DAYS.index(day) + days_later) % 7)
        current_day = WEEK_DAYS[selected_day]
        results += f", {current_day.title()} {get_days_later(days_later)}"

    else:  # add the days later
        results = " ".join((results, get_days_later(days_later)))

    return results.strip()