#!/usr/bin/env python

# THIS FILE IS PART OF THE CYLC SUITE ENGINE.
# Copyright (C) 2008-2018 NIWA
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
"""Wall clock related utilities."""

from calendar import timegm
from datetime import datetime, timedelta

from isodatetime.timezone import (
    get_local_time_zone_format, get_local_time_zone)

import cylc.flags


DATE_TIME_FORMAT_BASIC = "%Y%m%dT%H%M%S"
DATE_TIME_FORMAT_BASIC_SUB_SECOND = "%Y%m%dT%H%M%S.%f"
DATE_TIME_FORMAT_EXTENDED = "%Y-%m-%dT%H:%M:%S"
DATE_TIME_FORMAT_EXTENDED_SUB_SECOND = "%Y-%m-%dT%H:%M:%S.%f"

RE_DATE_TIME_FORMAT_EXTENDED = (
    r"\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(?:Z|[+-][\d:]+)?")

TIME_FORMAT_BASIC = "%H%M%S"
TIME_FORMAT_BASIC_SUB_SECOND = "%H%M%S.%f"
TIME_FORMAT_EXTENDED = "%H:%M:%S"
TIME_FORMAT_EXTENDED_SUB_SECOND = "%H:%M:%S.%f"

TIME_ZONE_STRING_LOCAL_BASIC = get_local_time_zone_format(reduced_mode=True)
TIME_ZONE_STRING_LOCAL_EXTENDED = get_local_time_zone_format(
    extended_mode=True, reduced_mode=True)
TIME_ZONE_STRING_UTC = "Z"
TIME_ZONE_UTC_UTC_OFFSET = (0, 0)
TIME_ZONE_LOCAL_UTC_OFFSET = get_local_time_zone()
TIME_ZONE_LOCAL_UTC_OFFSET_HOURS = TIME_ZONE_LOCAL_UTC_OFFSET[0]
TIME_ZONE_LOCAL_UTC_OFFSET_MINUTES = TIME_ZONE_LOCAL_UTC_OFFSET[1]

TIME_ZONE_LOCAL_INFO = {
    "hours": TIME_ZONE_LOCAL_UTC_OFFSET[0],
    "minutes": TIME_ZONE_LOCAL_UTC_OFFSET[1],
    "string_basic": TIME_ZONE_STRING_LOCAL_BASIC,
    "string_extended": TIME_ZONE_STRING_LOCAL_EXTENDED
}

TIME_ZONE_UTC_INFO = {
    "hours": TIME_ZONE_UTC_UTC_OFFSET[0],
    "minutes": TIME_ZONE_UTC_UTC_OFFSET[1],
    "string_basic": TIME_ZONE_STRING_UTC,
    "string_extended": TIME_ZONE_STRING_UTC
}

PARSER = None


def now(override_use_utc=None):
    """Return a current-time datetime.datetime and a UTC timezone flag.

    Keyword arguments:
    override_use_utc (default None) - a boolean (or None) that, if
    True, gives the date and time in UTC. If False, it gives the date
    and time in the local time zone. If None, the cylc.flags.utc boolean is
    used.

    """
    if override_use_utc or (override_use_utc is None and cylc.flags.utc):
        return datetime.utcnow(), False
    else:
        return datetime.now(), True


def get_current_time_string(display_sub_seconds=False, override_use_utc=None,
                            use_basic_format=False):
    """Return a string representing the current system time.

    Keyword arguments:
    display_sub_seconds (default False) - a boolean that, if True,
    switches on microsecond reporting
    override_use_utc (default None) - a boolean (or None) that, if
    True, switches on utc time zone reporting. If False, it switches
    off utc time zone reporting (even if cylc.flags.utc is True). If None,
    the cylc.flags.utc boolean is used.
    use_basic_format (default False) - a boolean that, if True,
    represents the date/time without "-" or ":" delimiters. This is
    most useful for filenames where ":" may cause problems.

    """
    date_time, date_time_is_local = now(override_use_utc=override_use_utc)
    return get_time_string(date_time, display_sub_seconds=display_sub_seconds,
                           override_use_utc=override_use_utc,
                           date_time_is_local=date_time_is_local,
                           use_basic_format=use_basic_format)


def get_time_string(date_time, display_sub_seconds=False,
                    override_use_utc=None, use_basic_format=False,
                    date_time_is_local=False, custom_time_zone_info=None):
    """Return a string representing the current system time.

    Arguments:
    date_time - a datetime.datetime object.

    Keyword arguments:
    display_sub_seconds (default False) - a boolean that, if True,
    switches on microsecond reporting
    override_use_utc (default None) - a boolean (or None) that, if
    True, switches on utc time zone reporting. If False, it switches
    off utc time zone reporting (even if cylc.flags.utc is True). If None,
    the cylc.flags.utc boolean is used.
    use_basic_format (default False) - a boolean that, if True,
    represents the date/time without "-" or ":" delimiters. This is
    most useful for filenames where ":" may cause problems.
    date_time_is_local - a boolean that, if True, indicates that
    the date_time argument object is in the local time zone, not UTC.
    custom_time_zone_info (default None) - a dictionary that enforces
    a particular time zone. It looks like {"hours": _hours,
    "minutes": _minutes, "string": _string} where _hours and _minutes
    are the hours and minutes offset from UTC and _string is the string
    to use as the time zone designator.

    """
    time_zone_string = None
    if custom_time_zone_info is not None:
        custom_hours = custom_time_zone_info["hours"]
        custom_minutes = custom_time_zone_info["minutes"]
        if use_basic_format:
            custom_string = custom_time_zone_info["string_basic"]
        else:
            custom_string = custom_time_zone_info["string_extended"]
        if date_time_is_local:
            date_time_hours = TIME_ZONE_LOCAL_UTC_OFFSET_HOURS
            date_time_minutes = TIME_ZONE_LOCAL_UTC_OFFSET_MINUTES
        else:
            date_time_hours, date_time_minutes = (0, 0)
        diff_hours = custom_hours - date_time_hours
        diff_minutes = custom_minutes - date_time_minutes
        date_time = date_time + timedelta(
            hours=diff_hours, minutes=diff_minutes)
        time_zone_string = custom_string
    elif override_use_utc or (override_use_utc is None and cylc.flags.utc):
        time_zone_string = TIME_ZONE_STRING_UTC
        if date_time_is_local:
            date_time = date_time - timedelta(
                hours=TIME_ZONE_LOCAL_UTC_OFFSET_HOURS,
                minutes=TIME_ZONE_LOCAL_UTC_OFFSET_MINUTES
            )
    else:
        if use_basic_format:
            time_zone_string = TIME_ZONE_STRING_LOCAL_BASIC
        else:
            time_zone_string = TIME_ZONE_STRING_LOCAL_EXTENDED
        if not date_time_is_local:
            diff_hours = TIME_ZONE_LOCAL_UTC_OFFSET_HOURS
            diff_minutes = TIME_ZONE_LOCAL_UTC_OFFSET_MINUTES
            date_time = date_time + timedelta(
                hours=diff_hours, minutes=diff_minutes)
    if use_basic_format:
        date_time_format_string = DATE_TIME_FORMAT_BASIC
        if display_sub_seconds:
            date_time_format_string = DATE_TIME_FORMAT_BASIC_SUB_SECOND
    else:
        date_time_format_string = DATE_TIME_FORMAT_EXTENDED
        if display_sub_seconds:
            date_time_format_string = DATE_TIME_FORMAT_EXTENDED_SUB_SECOND
    date_time_string = date_time.strftime(date_time_format_string)
    return date_time_string + time_zone_string


def get_time_string_from_unix_time(unix_time, display_sub_seconds=False,
                                   use_basic_format=False,
                                   custom_time_zone_info=None):
    """Convert a unix timestamp into a local time zone datetime.datetime.

    Arguments:
    unix_time - an integer or float number of seconds since the Unix
    epoch.

    Keyword arguments:
    display_sub_seconds (default False) - a boolean that, if True,
    switches on microsecond reporting
    use_basic_format (default False) - a boolean that, if True,
    represents the date/time without "-" or ":" delimiters. This is
    most useful for filenames where ":" may cause problems.
    custom_time_zone_info (default None) - a dictionary that enforces
    a particular time zone. It looks like {"hours": _hours,
    "minutes": _minutes, "string": _string} where _hours and _minutes
    are the hours and minutes offset from UTC and _string is the string
    to use as the time zone designator.

    """
    date_time = datetime.utcfromtimestamp(unix_time)
    return get_time_string(date_time,
                           display_sub_seconds=display_sub_seconds,
                           use_basic_format=use_basic_format,
                           override_use_utc=None,
                           date_time_is_local=False,
                           custom_time_zone_info=custom_time_zone_info)


def get_unix_time_from_time_string(datetime_string):
    """Convert a datetime string into a unix timestamp.

    The datetime_string must match DATE_TIME_FORMAT_EXTENDED above,
    which is the extended ISO 8601 year-month-dayThour:minute:second format,
    plus a valid ISO 8601 time zone. For example, 2016-09-07T11:21:00+01:00,
    2016-12-25T06:00:00Z, or 2016-12-25T06:00:00+13.

    isodatetime is not used to do the whole parsing, partly for performance,
    but mostly because the calendar may be in non-Gregorian mode.

    """
    try:
        date_time_utc = datetime.strptime(
            datetime_string, DATE_TIME_FORMAT_EXTENDED + "Z")
    except ValueError:
        global PARSER
        if PARSER is None:
            from isodatetime.parsers import TimePointParser
            PARSER = TimePointParser()
        time_zone_info = PARSER.get_info(datetime_string)[1]
        time_zone_hour = int(time_zone_info["time_zone_hour"])
        time_zone_minute = int(time_zone_info.get("time_zone_minute", 0))
        offset_seconds = 3600 * time_zone_hour + 60 * time_zone_minute
        if "+" in datetime_string:
            datetime_string = datetime_string.split("+")[0]
        else:
            datetime_string = datetime_string.rsplit("-", 1)[0]
        date_time = datetime.strptime(
            datetime_string, DATE_TIME_FORMAT_EXTENDED)
        date_time_utc = date_time - timedelta(seconds=offset_seconds)
    return timegm(date_time_utc.timetuple())


def get_seconds_as_interval_string(seconds):
    """Convert a number of seconds into an ISO 8601 duration string."""
    from isodatetime.data import Duration
    return str(Duration(seconds=seconds, standardize=True))
