import uuid
import json
from django.core.cache import cache

from .defaults import DEFAULTS, DEFAULTS_HASH
from .types import SettingType, coerce_from_storage, coerce_from_spec_default
from labs.utils.database_fields import get_default_fernet
from labs.models import SiteSetting as DBSiteSetting


NAMESPACE_KEY = "site_settings:NS"
ITEM_KEY_TMPL = f"site_settings:{DEFAULTS_HASH}:{{ns}}:{{key}}"
ITEM_KEY_TTL = 60 * 60 * 24 * 10  # 10 days

_MISS = object()


def _enc_set(key, value):
    raw = json.dumps(value).encode("utf-8")
    value = get_default_fernet().encrypt(raw)
    cache.set(key, value, ITEM_KEY_TTL)


def _enc_get(key):
    payload = cache.get(key)
    if payload is None:
        return _MISS
    try:
        raw = get_default_fernet().decrypt(payload)
        return json.loads(raw.decode("utf-8"))
    except (ValueError, json.JSONDecodeError):
        return _MISS


def get_namespace():
    ns = cache.get(NAMESPACE_KEY)
    if not ns:
        ns = uuid.uuid4().hex
        cache.set(NAMESPACE_KEY, ns, None)
    return ns


def bump_namespace():
    cache.set(NAMESPACE_KEY, uuid.uuid4().hex, None)


def _fetch_from_db(key):
    try:
        obj = DBSiteSetting.objects.only("key_type", "value").get(key=key)
        t = SettingType(obj.key_type)
        return coerce_from_storage(t, obj.value)
    except DBSiteSetting.DoesNotExist:
        return None


def _default_for(key):
    spec = DEFAULTS.get(key)
    if not spec:
        raise AttributeError(f"Unknown setting '{key}' (not in defaults.yaml)")
    t = SettingType(spec["type"])
    return coerce_from_spec_default(t, spec["default"])


def get(key):
    if key not in DEFAULTS:
        raise AttributeError(f"Unknown setting '{key}' (not in defaults.yaml)")

    ns = get_namespace()
    cache_key = ITEM_KEY_TMPL.format(ns=ns, key=key)
    hit = _enc_get(cache_key)
    if hit is not _MISS:
        return hit

    value = _fetch_from_db(key)

    if value is None:
        value = _default_for(key)

    _enc_set(cache_key, value)
    return value


class _LazySettings:
    def __getattr__(self, name: str):
        return get(name)

    def __getitem__(self, name: str):
        return get(name)

    def refresh(self):
        bump_namespace()


SiteSettings = _LazySettings()