# -*- coding: utf-8 -*-
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals

from datetime import datetime, date, timedelta
from dateutil.relativedelta import relativedelta  # for doctest
import six

from croniter import croniter


cron_presets = {
    '@hourly': '0 * * * *',
    '@daily': '0 0 * * *',
    '@weekly': '0 0 * * 0',
    '@monthly': '0 0 1 * *',
    '@yearly': '0 0 1 1 *',
}


def date_range(
        start_date,
        end_date=None,
        num=None,
        delta=None):
    """
    Get a set of dates as a list based on a start, end and delta, delta
    can be something that can be added to ``datetime.datetime``
    or a cron expression as a ``str``

    :param start_date: anchor date to start the series from
    :type start_date: datetime.datetime
    :param end_date: right boundary for the date range
    :type end_date: datetime.datetime
    :param num: alternatively to end_date, you can specify the number of
        number of entries you want in the range. This number can be negative,
        output will always be sorted regardless
    :type num: int

    >>> date_range(datetime(2016, 1, 1), datetime(2016, 1, 3), delta=timedelta(1))
    [datetime.datetime(2016, 1, 1, 0, 0), datetime.datetime(2016, 1, 2, 0, 0), datetime.datetime(2016, 1, 3, 0, 0)]
    >>> date_range(datetime(2016, 1, 1), datetime(2016, 1, 3), delta='0 0 * * *')
    [datetime.datetime(2016, 1, 1, 0, 0), datetime.datetime(2016, 1, 2, 0, 0), datetime.datetime(2016, 1, 3, 0, 0)]
    >>> date_range(datetime(2016, 1, 1), datetime(2016, 3, 3), delta="0 0 0 * *")
    [datetime.datetime(2016, 1, 1, 0, 0), datetime.datetime(2016, 2, 1, 0, 0), datetime.datetime(2016, 3, 1, 0, 0)]
    """
    if not delta:
        return []
    if end_date and start_date > end_date:
        raise Exception("Wait. start_date needs to be before end_date")
    if end_date and num:
        raise Exception("Wait. Either specify end_date OR num")
    if not end_date and not num:
        end_date = datetime.now()

    delta_iscron = False
    if isinstance(delta, six.string_types):
        delta_iscron = True
        cron = croniter(delta, start_date)
    elif isinstance(delta, timedelta):
        delta = abs(delta)
    l = []
    if end_date:
        while start_date <= end_date:
            l.append(start_date)
            if delta_iscron:
                start_date = cron.get_next(datetime)
            else:
                start_date += delta
    else:
        for i in range(abs(num)):
            l.append(start_date)
            if delta_iscron:
                if num > 0:
                    start_date = cron.get_next(datetime)
                else:
                    start_date = cron.get_prev(datetime)
            else:
                if num > 0:
                    start_date += delta
                else:
                    start_date -= delta
    return sorted(l)


def round_time(dt, delta, start_date=datetime.min):
    """
    Returns the datetime of the form start_date + i * delta
    which is closest to dt for any non-negative integer i.

    Note that delta may be a datetime.timedelta or a dateutil.relativedelta

    >>> round_time(datetime(2015, 1, 1, 6), timedelta(days=1))
    datetime.datetime(2015, 1, 1, 0, 0)
    >>> round_time(datetime(2015, 1, 2), relativedelta(months=1))
    datetime.datetime(2015, 1, 1, 0, 0)
    >>> round_time(datetime(2015, 9, 16, 0, 0), timedelta(1), datetime(2015, 9, 14, 0, 0))
    datetime.datetime(2015, 9, 16, 0, 0)
    >>> round_time(datetime(2015, 9, 15, 0, 0), timedelta(1), datetime(2015, 9, 14, 0, 0))
    datetime.datetime(2015, 9, 15, 0, 0)
    >>> round_time(datetime(2015, 9, 14, 0, 0), timedelta(1), datetime(2015, 9, 14, 0, 0))
    datetime.datetime(2015, 9, 14, 0, 0)
    >>> round_time(datetime(2015, 9, 13, 0, 0), timedelta(1), datetime(2015, 9, 14, 0, 0))
    datetime.datetime(2015, 9, 14, 0, 0)
    """

    if isinstance(delta, six.string_types):
        # It's cron based, so it's easy
        cron = croniter(delta, start_date)
        prev = cron.get_prev(datetime)
        if prev == start_date:
            return start_date
        else:
            return prev

    # Ignore the microseconds of dt
    dt -= timedelta(microseconds=dt.microsecond)

    # We are looking for a datetime in the form start_date + i * delta
    # which is as close as possible to dt. Since delta could be a relative
    # delta we don't know it's exact length in seconds so we cannot rely on
    # division to find i. Instead we employ a binary search algorithm, first
    # finding an upper and lower limit and then disecting the interval until
    # we have found the closest match.

    # We first search an upper limit for i for which start_date + upper * delta
    # exceeds dt.
    upper = 1
    while start_date + upper*delta < dt:
        # To speed up finding an upper limit we grow this exponentially by a
        # factor of 2
        upper *= 2

    # Since upper is the first value for which start_date + upper * delta
    # exceeds dt, upper // 2 is below dt and therefore forms a lower limited
    # for the i we are looking for
    lower = upper // 2

    # We now continue to intersect the interval between
    # start_date + lower * delta and start_date + upper * delta
    # until we find the closest value
    while True:
        # Invariant: start + lower * delta < dt <= start + upper * delta
        # If start_date + (lower + 1)*delta exceeds dt, then either lower or
        # lower+1 has to be the solution we are searching for
        if start_date + (lower + 1)*delta >= dt:
            # Check if start_date + (lower + 1)*delta or
            # start_date + lower*delta is closer to dt and return the solution
            if (
                    (start_date + (lower + 1) * delta) - dt <=
                    dt - (start_date + lower * delta)):
                return start_date + (lower + 1)*delta
            else:
                return start_date + lower * delta

        # We intersect the interval and either replace the lower or upper
        # limit with the candidate
        candidate = lower + (upper - lower) // 2
        if start_date + candidate*delta >= dt:
            upper = candidate
        else:
            lower = candidate

    # in the special case when start_date > dt the search for upper will
    # immediately stop for upper == 1 which results in lower = upper // 2 = 0
    # and this function returns start_date.
