#!/usr/bin/env python3
"""Encoding normalization and selection policy with Enum support."""
from __future__ import annotations
from enum import Enum
from typing import Optional, Tuple, Union, Sequence
class GnmiEncoding(Enum):
JSON_IETF = "json_ietf"
JSON = "json"
ASCII = "ascii"
def __str__(self) -> str: # pragma: no cover - trivial
return self.value
@classmethod
def from_any(
cls, value: Optional[Union[str, "GnmiEncoding"]]
) -> Optional["GnmiEncoding"]:
"""Parse various inputs to a GnmiEncoding enum.
- If enum is provided, return it.
- If string is provided, case-normalize and map to enum.
- Otherwise return None.
"""
if value is None:
return None
if isinstance(value, GnmiEncoding):
return value
s = str(value).strip().lower()
if s == "json_ietf":
return GnmiEncoding.JSON_IETF
if s == "json":
return GnmiEncoding.JSON
if s == "ascii":
return GnmiEncoding.ASCII
return None
class EncodingPolicy:
"""Normalize inputs to enums and choose supported fallbacks (as enums)."""
def normalize(
self, encoding: Optional[Union[str, GnmiEncoding]]
) -> Optional[GnmiEncoding]:
return GnmiEncoding.from_any(encoding)
def choose_supported(
self,
requested: Optional[Union[str, GnmiEncoding]],
supported: Sequence[Union[str, GnmiEncoding]],
) -> Tuple[Optional[GnmiEncoding], bool]:
"""Return (selected_encoding_enum, used_fallback)."""
sup: set[GnmiEncoding] = {
e for e in (self.normalize(x) for x in supported) if e is not None
}
req = self.normalize(requested) if requested is not None else None
if req is None:
# No request -> prefer best available
for candidate in (
GnmiEncoding.JSON_IETF,
GnmiEncoding.JSON,
GnmiEncoding.ASCII,
):
if candidate in sup:
return candidate, False
return None, False
if req in sup:
return req, False
# Conservative fallback policy: only allow fallback to ASCII
fallbacks: dict[GnmiEncoding, tuple[GnmiEncoding, ...]] = {
GnmiEncoding.JSON_IETF: (GnmiEncoding.ASCII,),
GnmiEncoding.JSON: (GnmiEncoding.ASCII,),
GnmiEncoding.ASCII: (),
}
for cand in fallbacks.get(req, ()):
if cand in sup:
return cand, True
return None, False
