#!/usr/bin/python

import datetime
import re
import string


_valid_keywords = ['last', 'this', 'next']


class Unit(object):

    def __str__(self):
        return self.ref.isoformat()

    def __init__(self, ref):
        self.ref = ref if ref else datetime.datetime.now()

    def seekb(self):
        return self._seek(-1)

    def seekf(self):
        return self._seek(1)

    def nseekb(self):
        return self._nseek(-1)

    def nseekf(self):
        return self._nseek(1)

    @staticmethod
    def make(name, ref=None):
        _valid = {
            'day': Day,
            'hour': Hour,
            'minute': Minute,
            'month': Month,
            'second': Second,
            'week': Week,
            'year': Year,
        }
        if name not in _valid.keys():
            raise ValueError("invalid unit name: %s" % name)
        return _valid[name](ref)

    def apply_offset(self, offset):
        new = self
        while offset:
            if offset > 0:
                new = new.seekf()
                offset = offset - 1
            elif offset < 0:
                new = new.seekb()
                offset = offset + 1
        return new


class Second(Unit):

    def start(self):
        return Second(ref=datetime.datetime(
            self.ref.year,
            self.ref.month,
            self.ref.day,
            self.ref.hour,
            self.ref.minute,
            self.ref.second,
        ))

    def end(self):
        return Second(ref=datetime.datetime(
            self.ref.year,
            self.ref.month,
            self.ref.day,
            self.ref.hour,
            self.ref.minute,
            self.ref.second,
        ))

    def _seek(self, step):
        #
        # Seek to next/previous second
        #
        if step > 0:
            otherref = self.ref + datetime.timedelta(seconds=abs(step))
        elif step < 0:
            otherref = self.ref - datetime.timedelta(seconds=abs(step))
        else:
            otherref = self.ref
        return Second(ref=datetime.datetime(
            otherref.year,
            otherref.month,
            otherref.day,
            otherref.hour,
            otherref.minute,
            otherref.second,
        ))


class Minute(Unit):

    def start(self):
        return Minute(ref=datetime.datetime(
            self.ref.year,
            self.ref.month,
            self.ref.day,
            self.ref.hour,
            self.ref.minute,
            datetime.datetime.min.second,
        ))

    def end(self):
        return Minute(ref=datetime.datetime(
            self.ref.year,
            self.ref.month,
            self.ref.day,
            self.ref.hour,
            self.ref.minute,
            datetime.datetime.max.second,
        ))

    def _seek(self, step):
        #
        # Seek to next/previous minute
        #
        if step > 0:
            otherref = self.ref + datetime.timedelta(seconds=abs(step) * 60)
        elif step < 0:
            otherref = self.ref - datetime.timedelta(seconds=abs(step) * 60)
        else:
            otherref = self.ref
        return Minute(ref=datetime.datetime(
            otherref.year,
            otherref.month,
            otherref.day,
            otherref.hour,
            otherref.minute,
            otherref.second,
        ))


class Hour(Unit):

    def start(self):
        return Hour(ref=datetime.datetime(
            self.ref.year,
            self.ref.month,
            self.ref.day,
            self.ref.hour,
            datetime.datetime.min.minute,
            datetime.datetime.min.second,
        ))

    def end(self):
        return Hour(ref=datetime.datetime(
            self.ref.year,
            self.ref.month,
            self.ref.day,
            self.ref.hour,
            datetime.datetime.max.minute,
            datetime.datetime.max.second,
        ))

    def _seek(self, step):
        #
        # Seek to next/previous minute
        #
        if step > 0:
            otherref = self.ref + datetime.timedelta(seconds=abs(step) * 3600)
        elif step < 0:
            otherref = self.ref - datetime.timedelta(seconds=abs(step) * 3600)
        else:
            otherref = self.ref
        return Hour(ref=datetime.datetime(
            otherref.year,
            otherref.month,
            otherref.day,
            otherref.hour,
            otherref.minute,
            otherref.second,
        ))


class Day(Unit):

    def start(self):
        return Day(ref=datetime.datetime(
            self.ref.year,
            self.ref.month,
            self.ref.day,
            datetime.datetime.min.hour,
            datetime.datetime.min.minute,
            datetime.datetime.min.second,
        ))

    def end(self):
        return Day(ref=datetime.datetime(
            self.ref.year,
            self.ref.month,
            self.ref.day,
            datetime.datetime.max.hour,
            datetime.datetime.max.minute,
            datetime.datetime.max.second,
        ))

    def _seek(self, step):
        #
        # Seek to next/previous day
        #
        bigdelta = datetime.timedelta(days=step)
        return Day(ref=self.ref + bigdelta)

    def _nseek(self, step):
        #
        # Almost seek to next/previous day
        #
        return Day(ref=datetime.datetime(
            self.ref.year,
            self.ref.month,
            self.ref.day,
            self.ref.hour,
            self.ref.minute,
            self.ref.second,
        ))


class Week(Unit):

    def start(self):
        early = self.nseekb()
        return Week(ref=datetime.datetime(
            early.ref.year,
            early.ref.month,
            early.ref.day,
            datetime.datetime.min.hour,
            datetime.datetime.min.minute,
            datetime.datetime.min.second,
        ))

    def end(self):
        late = self.nseekf()
        return Week(ref=datetime.datetime(
            late.ref.year,
            late.ref.month,
            late.ref.day,
            datetime.datetime.max.hour,
            datetime.datetime.max.minute,
            datetime.datetime.max.second,
        ))

    def _seek(self, step):
        #
        # Seek to next/previous week
        #
        delta = datetime.timedelta(days=step)
        newref = self.ref
        while newref.isocalendar()[1] == self.ref.isocalendar()[1]:
            newref = newref + delta
        return Week(ref=newref)

    def _nseek(self, step):
        #
        # Almost seek to next/previous week
        #
        delta = datetime.timedelta(days=step)
        newref = self.ref
        while newref.isocalendar()[1] == self.ref.isocalendar()[1]:
            newref = newref + delta
        return Month(ref=newref - delta)


class Month(Unit):

    def start(self):
        early = self.nseekb()
        return Month(ref=datetime.datetime(
            early.ref.year,
            early.ref.month,
            early.ref.day,
            datetime.datetime.min.hour,
            datetime.datetime.min.minute,
            datetime.datetime.min.second,
        ))

    def end(self):
        late = self.nseekf()
        return Month(ref=datetime.datetime(
            late.ref.year,
            late.ref.month,
            late.ref.day,
            datetime.datetime.max.hour,
            datetime.datetime.max.minute,
            datetime.datetime.max.second,
        ))

    def _seek(self, step):
        #
        # Seek to next/previous month
        #
        delta = datetime.timedelta(days=step)
        newref = self.ref
        while newref.month == self.ref.month:
            newref = newref + delta
        return Month(ref=newref)

    def _nseek(self, step):
        #
        # Almost seek to next/previous month
        #
        delta = datetime.timedelta(days=step)
        newref = self.ref
        while newref.month == self.ref.month:
            newref = newref + delta
        return Month(ref=newref - delta)


class Year(Unit):

    def start(self):
        return Year(ref=datetime.datetime(
            self.ref.year,
            datetime.datetime.min.month,
            datetime.datetime.min.day,
            datetime.datetime.min.hour,
            datetime.datetime.min.minute,
            datetime.datetime.min.second,
        ))

    def end(self):
        return Year(ref=datetime.datetime(
            self.ref.year,
            datetime.datetime.max.month,
            datetime.datetime.max.day,
            datetime.datetime.max.hour,
            datetime.datetime.max.minute,
            datetime.datetime.max.second,
        ))

    def apply_offset(self, offset):
        return Year(ref=datetime.datetime(
            self.ref.year + offset,
            self.ref.month,
            self.ref.day,
            self.ref.hour,
            self.ref.minute,
            self.ref.second,
        ))


def parse_offset(text):
    m = re.match('^(last|this|next)([+-]+|[+-][0-9]+)?$', text)
    if not m:
        raise ValueError('bad offset phrase: %s' % text)
    direction, offphrase = m.groups()
    if direction == 'this':
        amount = 0
    elif direction == 'next':
        amount = 1
    elif direction == 'last':
        amount = -1
    if not offphrase:
        pass
    elif offphrase[-1] in string.digits:
        sign, number = re.match('([+-])([0-9]+)', offphrase).groups()
        if sign == '+':
            amount = amount + int(number)
        else:
            amount = amount - int(number)
    else:
        for char in offphrase:
            if char == '+':
                amount = amount + 1
            else:
                amount = amount - 1
    return amount


class Range(object):

    def start(self):
        return self.unit.start()

    def end(self):
        return self.unit.end()

    def __init__(self, offset, unitname):
        self.unit = Unit.make(unitname).apply_offset(parse_offset(offset))