from datetime import datetime, timedelta, timezone
import pytz


def _suffix(d):
    return 'th' if 11 <= d <= 13 else {1: 'st', 2: 'nd', 3: 'rd'}.get(d % 10, 'th')


class Day:
    def __init__(self, year, month, day, user):
        self.user = user
        self._timestamp = datetime(year, month, day, tzinfo=timezone.utc)

    @staticmethod
    def from_str(string, user):
        return Day._from_timestamp(datetime.strptime(string, "%Y-%m-%d"), user)

    @staticmethod
    def _from_timestamp(timestamp, user):
        # not exposed because it is only an utilty function, not aware of the
        # user's time zone and start-of-day hour
        return Day(timestamp.year, timestamp.month, timestamp.day, user)

    def __eq__(self, other):
        if not isinstance(other, self.__class__):
            return False
        return self.year == other.year \
            and self.month == other.month \
            and self.day == other.day

    def __add__(self, other, oper="+"):
        if not isinstance(other, int):
            raise TypeError(
                'Unsupported operands for "+". The right hand side needs to be a number.')
        else:
            return Day._from_timestamp(self.timestamp + timedelta(days=other), self.user)

    def __sub__(self, other):
        if not isinstance(other, int):
            raise TypeError(
                'Unsupported operands for "-". The right hand side needs to be a number.')
        else:
            return Day._from_timestamp(self.timestamp + timedelta(days=-other), self.user)

    def __lt__(self, other): return self.timestamp < other.timestamp
    def __gt__(self, other): return self.timestamp > other.timestamp
    def __le__(self, other): return self < other or self == other
    def __ge__(self, other): return self > other or self == other

    def __repr__(self): return "<Day[%s,user=%s]>" % (self.url, self.user)

    @property
    def year(self): return self._timestamp.year

    @property
    def month(self): return self._timestamp.month

    @property
    def day(self): return self._timestamp.day

    @property
    def timestamp(self): return self._timestamp

    @property
    def is_today(self):
        return self == Day.today(self.user)

    @property
    def is_future(self):
        return self > Day.today(self.user)

    @property
    def pretty(self):
        if self.is_today:
            return "Today"
        return self._timestamp.strftime("%B {S}, %Y").replace('{S}', str(self.day) + _suffix(self.day))

    @property
    def url(self):
        return self._timestamp.strftime("%Y-%m-%d")

    @staticmethod
    def today(user):
        tz = pytz.timezone(user.timezone)

        now = datetime.now(tz)
        day = Day(now.year, now.month, now.day, user)

        if now.hour < user.start_of_day:
            day -= 1

        return day