from datetime import datetime


def _ordinal(day):
    SUFFIX = {
        1: 'st',
        2: 'nd',
        3: 'rd',
    }
    if day in [11, 12, 13]:
        suffix = 'th'
    else:
        last_digit = int(str(day)[-1])
        suffix = SUFFIX.get(last_digit, 'th')
    return '{day}{suffix}'.format(day=day, suffix=suffix)


def _hour_to_str(date):
    return date.strftime('%-I %p')


def _str_to_date(date_str):
    return datetime.strptime(date_str, "%Y-%m-%dT%H:%M:%SZ")


def _month_str(days, month):
    return '{days} {month}'.format(
        days=', '.join(days),
        month=month,
    )


def humanizeTransmissionDates(datesAsStrings):
    date_parts = []
    current_month = []
    month_parts = []

    for date_str in datesAsStrings:
        dt = _str_to_date(date_str)
        month = dt.strftime('%B')
        day = _ordinal(dt.day)

        if month == current_month:
            month_parts.append(day)
        else:
            if current_month:
                date_parts.append(_month_str(days=month_parts, month=current_month))

            month_parts = [day]
            current_month = month

        time_str = _hour_to_str(dt)



    if date_parts:
        humanized = '{all_months}, and '.format(
            all_months=', '.join(date_parts),
        )
    else:
        humanized = ''

    humanized = '{humanized}{last_month} at {time_str}'.format(
        humanized=humanized,
        last_month=_month_str(days=month_parts, month=current_month),
        time_str=time_str,
    )
    return humanized