from aiohttp import web
from apollo_utils.service.exceptions import UnsupportedCacheMode
from contextvars import ContextVar
from enum import Enum

from server import config


class CacheMode(Enum):
    """Supported cache modes.
    REGULAR - regular usage: first try to find data in cache, if nothing was found, load new data and store it in cache.
    UPDATE - do not check cache, load new data and store it in cache.
    IGNORE - load new data and return it without saving to cache.
    """

    REGULAR = "regular"
    UPDATE = "update"
    IGNORE = "ignore"

    @classmethod
    def has(cls, value):
        return value in cls._value2member_map_


DEFAULT_CACHE_MODE = CacheMode.REGULAR

cache_mode = ContextVar("cache_mode", default=DEFAULT_CACHE_MODE)


def set_cache_mode(request: web.Request):
    """Set cache mode based on headers value and configuration."""
    mode = request.headers.get("Cache-Mode")
    if not mode or not config.ALLOW_CACHE_MODES:
        return
    if not CacheMode.has(mode):
        raise UnsupportedCacheMode(f"Got unsupported cache mode value {mode}")
    cache_mode.set(CacheMode(mode))