from __future__ import absolute_import
from __future__ import division
# Copyright (c) 2010-2017 openpyxl

"""Manage Excel date weirdness."""

# Python stdlib imports
import datetime
from datetime import timedelta, tzinfo
from math import isnan
import re

from jdcal import (
    gcal2jd,
    jd2gcal,
    MJD_0
)


# constants
MAC_EPOCH = datetime.date(1904, 1, 1)
WINDOWS_EPOCH = datetime.date(1899, 12, 30)
CALENDAR_WINDOWS_1900 = sum(gcal2jd(WINDOWS_EPOCH.year, WINDOWS_EPOCH.month, WINDOWS_EPOCH.day))
CALENDAR_MAC_1904 = sum(gcal2jd(MAC_EPOCH.year, MAC_EPOCH.month, MAC_EPOCH.day))
SECS_PER_DAY = 86400

EPOCH = datetime.datetime.utcfromtimestamp(0)
ISO_FORMAT = '%Y-%m-%dT%H:%M:%SZ'
ISO_REGEX = re.compile(r'''
(?P<date>(?P<year>\d{4})-(?P<month>\d{2})-(?P<day>\d{2}))?T?
(?P<time>(?P<hour>\d{2}):(?P<minute>\d{2}):(?P<second>\d{2})(.(?P<ms>\d{2}))?)?Z?''',
                                       re.VERBOSE)


def to_ISO8601(dt):
    """Convert from a datetime to a timestamp string."""
    return datetime.datetime.strftime(dt, ISO_FORMAT)


def from_ISO8601(formatted_string):
    """Convert from a timestamp string to a datetime object. According to
    18.17.4 in the specification the following ISO 8601 formats are
    supported.

    Dates B.1.1 and B.2.1
    Times B.1.2 and B.2.2
    Datetimes B.1.3 and B.2.3

    There is no concept of timedeltas
    """
    match = ISO_REGEX.match(formatted_string)
    if not match:
        raise ValueError("Invalid datetime value {}".format(formatted_string))

    parts = {k:int(v) for k, v in match.groupdict().items() if v is not None and v.isdigit()}
    if 'year' not in parts:
        dt = datetime.time(parts['hour'], parts['minute'], parts['second'])
    elif 'hour' not in parts:
        dt = datetime.date(parts['year'], parts['month'], parts['day'])
    else:
        dt = datetime.datetime(year=parts['year'], month=parts['month'],
                               day=parts['day'], hour=parts['hour'], minute=parts['minute'],
                               second=parts['second'])
    if 'ms' in parts:
        dt += timedelta(microseconds=parts['ms'])
    return dt


def to_excel(dt, offset=CALENDAR_WINDOWS_1900):
    if isinstance(dt, datetime.time):
        return time_to_days(dt)
    if isinstance(dt, datetime.timedelta):
        return timedelta_to_days(dt)
    if isnan(dt.year): # Pandas supports Not a Date
        return
    jul = sum(gcal2jd(dt.year, dt.month, dt.day)) - offset
    if jul <= 60 and offset == CALENDAR_WINDOWS_1900:
        jul -= 1
    if hasattr(dt, 'time'):
        jul += time_to_days(dt)
    return jul


def from_excel(value, offset=CALENDAR_WINDOWS_1900):
    if value is None:
        return
    if 1 < value < 60 and offset == CALENDAR_WINDOWS_1900:
        value += 1
    parts = list(jd2gcal(MJD_0, value + offset - MJD_0))
    _, fraction = divmod(value, 1)
    jumped = (parts[-1] == 0 and fraction > 0)
    diff = datetime.timedelta(days=fraction)

    if 0 < abs(value) < 1:
        return days_to_time(diff)
    if not jumped:
        return datetime.datetime(*parts[:3]) + diff
    else:
        return datetime.datetime(*parts[:3] + [0])


class GMT(tzinfo):

    def utcoffset(self, dt):
        return timedelta(0)

    def dst(self, dt):
        return timedelta(0)

    def tzname(self,dt):
        return "GMT"

try:
    from datetime import timezone
    UTC = timezone(timedelta(0))
except ImportError:
    # Python 2
    UTC = GMT()


def time_to_days(value):
    """Convert a time value to fractions of day"""
    if value.tzinfo is not None:
        value = value.astimezone(UTC)
    return (
        (value.hour * 3600)
        + (value.minute * 60)
        + value.second
        + value.microsecond / 10**6
        ) / SECS_PER_DAY


def timedelta_to_days(value):
    """Convert a timedelta value to fractions of a day"""
    if not hasattr(value, 'total_seconds'):
        secs = (value.microseconds +
                (value.seconds + value.days * SECS_PER_DAY) * 10**6) / 10**6
    else:
        secs = value.total_seconds()
    return secs / SECS_PER_DAY


def days_to_time(value):
    mins, seconds = divmod(value.seconds, 60)
    hours, mins = divmod(mins, 60)
    return datetime.time(hours, mins, seconds, value.microseconds)
