"""Time helpers.

* Camera local
* System local
* UTC

Timestamp to datetime
    * Timestamp
      * in UTC
    * Timezone
      * Implicit system local timezone
      * No known timezone
      * Known timezone

Datetime to timestamp
    * always store as local time
    * optionally with UTC offset

Part of the tagit module.
A copy of the license is provided with the project.
Author: Matthias Baumgartner, 2022
"""
# standard imports
from datetime import timezone, datetime, tzinfo, timedelta

# exports
__all__ = ('timestamp', 'from_timestamp')


## code ##

timestamp_loc = lambda dt: dt.replace(tzinfo=timezone.utc).timestamp()

timestamp_utc = lambda dt: dt.timestamp()

from_timestamp_loc = lambda ts: datetime.utcfromtimestamp(ts)

from_timestamp_utc = lambda ts: datetime.fromtimestamp(ts)

now = datetime.now

timestamp_min = timestamp_loc(datetime.min)

timestamp_max = timestamp_loc(datetime.max)

def utcoffset(dt):
    if dt.tzinfo is None:
        return local_tzo(dt)
    elif dt.tzinfo is NoTimeZone:
        return None
    else:
        return dt.tzinfo.utcoffset(dt).total_seconds() / 3600

NoTimeZone = timezone(timedelta(0), 'NoTimeZone')

def local_tzo(dt=None):
    """Return the offset between the local time and UTC.
    (i.e. return the x of UTC+x).
    """
    dt = datetime.now() if dt is None else dt
    return (timestamp_loc(dt) - dt.timestamp()) / 3600

## EOF ##