"""This module identifies timezones.

Normally, timezones have ids.
This is a way to access the ids if you have a
datetime.tzinfo object.
"""

from __future__ import annotations

from collections import defaultdict
from pathlib import Path
from typing import TYPE_CHECKING, Optional

from dateutil.tz import tz

from icalendar.timezone import equivalent_timezone_ids_result

if TYPE_CHECKING:
    from datetime import datetime, tzinfo

DATEUTIL_UTC = tz.gettz("UTC")
DATEUTIL_UTC_PATH : Optional[str] = getattr(DATEUTIL_UTC, "_filename", None)
DATEUTIL_ZONEINFO_PATH = (
    None if DATEUTIL_UTC_PATH is None else Path(DATEUTIL_UTC_PATH).parent
)

def tzids_from_tzinfo(tzinfo: Optional[tzinfo]) -> tuple[str]:
    """Get several timezone ids if we can identify the timezone.

    >>> import zoneinfo
    >>> from icalendar.timezone.tzid import tzids_from_tzinfo
    >>> tzids_from_tzinfo(zoneinfo.ZoneInfo("Arctic/Longyearbyen"))
    ('Arctic/Longyearbyen', 'Atlantic/Jan_Mayen', 'Europe/Berlin', 'Europe/Budapest', 'Europe/Copenhagen', 'Europe/Oslo', 'Europe/Stockholm', 'Europe/Vienna')
    >>> from dateutil.tz import gettz
    >>> tzids_from_tzinfo(gettz("Europe/Berlin"))
    ('Europe/Berlin', 'Arctic/Longyearbyen', 'Atlantic/Jan_Mayen', 'Europe/Budapest', 'Europe/Copenhagen', 'Europe/Oslo', 'Europe/Stockholm', 'Europe/Vienna')

    """  # The example might need to change if you recreate the lookup tree
    if tzinfo is None:
        return ()
    if hasattr(tzinfo, "zone"):
        return get_equivalent_tzids(tzinfo.zone)  # pytz implementation
    if hasattr(tzinfo, "key"):
        return get_equivalent_tzids(tzinfo.key)  # ZoneInfo implementation
    if isinstance(tzinfo, tz._tzicalvtz):  # noqa: SLF001
        return get_equivalent_tzids(tzinfo._tzid)  # noqa: SLF001
    if isinstance(tzinfo, tz.tzstr):
        return get_equivalent_tzids(tzinfo._s)  # noqa: SLF001
    if hasattr(tzinfo, "_filename"): # dateutil.tz.tzfile  # noqa: SIM102
        if DATEUTIL_ZONEINFO_PATH is not None:
            # tzfile('/usr/share/zoneinfo/Europe/Berlin')
            path = tzinfo._filename  # noqa: SLF001
            if path.startswith(str(DATEUTIL_ZONEINFO_PATH)):
                tzid = str(Path(path).relative_to(DATEUTIL_ZONEINFO_PATH))
                return get_equivalent_tzids(tzid)
            return get_equivalent_tzids(path)
    if isinstance(tzinfo, tz.tzutc):
        return get_equivalent_tzids("UTC")
    return ()


def tzid_from_tzinfo(tzinfo: Optional[tzinfo]) -> Optional[str]:
    """Retrieve the timezone id from the tzinfo object.

    Some timezones are equivalent.
    Thus, we might return one ID that is equivelant to others.
    """
    tzids = tzids_from_tzinfo(tzinfo)
    if "UTC" in tzids:
        return "UTC"
    if not tzids:
        return None
    return tzids[0]


def tzid_from_dt(dt: datetime) -> Optional[str]:
    """Retrieve the timezone id from the datetime object."""
    tzid = tzid_from_tzinfo(dt.tzinfo)
    if tzid is None:
        return dt.tzname()
    return tzid


_EQUIVALENT_IDS : dict[str, set[str]] = defaultdict(set)

def _add_equivalent_ids(value:tuple|dict|set):
    """This adds equivalent ids/

    As soon as one timezone implementation used claims their equivalence, 
    they are considered equivalent.
    Have a look at icalendar.timezone.equivalent_timezone_ids.
    """
    if isinstance(value, set):
        for tzid in value:
            _EQUIVALENT_IDS[tzid].update(value)
    elif isinstance(value, tuple):
        _add_equivalent_ids(value[1])
    elif isinstance(value, dict):
        for value in value.values():
            _add_equivalent_ids(value)
    else:
        raise TypeError(f"Expected tuple, dict or set, not {value.__class__.__name__}: {value!r}")

_add_equivalent_ids(equivalent_timezone_ids_result.lookup)

def get_equivalent_tzids(tzid: str) -> tuple[str]:
    """This returns the tzids which are equivalent to this one."""
    ids = _EQUIVALENT_IDS.get(tzid, set())
    return (tzid,) + tuple(sorted(ids - {tzid}))


__all__ = ["tzid_from_tzinfo", "tzid_from_dt", "tzids_from_tzinfo"]