"""Classical evaluation backend protocol (L3 FEN cache / prefill)."""

from __future__ import annotations

from typing import Protocol, runtime_checkable

from chess_tutor.classical_eval import PositionAnalysis

DEFAULT_BACKEND_ID = "python"


@runtime_checkable
class ClassicalEvalBackend(Protocol):
    """Analyze a FEN with the classical component model."""

    @property
    def backend_id(self) -> str:
        """Stable id included in FEN cache version strings."""

    def analyze_fen(self, fen: str) -> PositionAnalysis:
        ...