"""
Timezone utilities

Just UTC-awareness right now
"""
# Copyright (c) Jupyter Development Team.
# Distributed under the terms of the Modified BSD License.
from datetime import datetime, timedelta, tzinfo

# constant for zero offset
ZERO = timedelta(0)


class tzUTC(tzinfo):  # noqa
    """tzinfo object for UTC (zero offset)"""

    def utcoffset(self, d):
        """Compute utcoffset."""
        return ZERO

    def dst(self, d):
        """Compute dst."""
        return ZERO


UTC = tzUTC()


def utc_aware(unaware):
    """decorator for adding UTC tzinfo to datetime's utcfoo methods"""

    def utc_method(*args, **kwargs):
        dt = unaware(*args, **kwargs)
        return dt.replace(tzinfo=UTC)

    return utc_method


utcfromtimestamp = utc_aware(datetime.utcfromtimestamp)
utcnow = utc_aware(datetime.utcnow)


def isoformat(dt):
    """Return iso-formatted timestamp

    Like .isoformat(), but uses Z for UTC instead of +00:00
    """
    return dt.isoformat().replace("+00:00", "Z")
