# app/models/decoding/base.py
from abc import ABC, abstractmethod

import torch

from models.runtime.state import GenerationState


class DecodingPolicy(ABC):
    """
    Token-level decoding policy.

    Responsibilities:
    - Select the next token from logits
    - Decide whether generation should stop

    This policy MUST be stateless or derive state only
    from GenerationState.
    """

    supports_sampling: bool = False
    supports_streaming: bool = False

    @abstractmethod
    def select(
        self,
        logits: torch.Tensor,
        state: GenerationState,
    ) -> int:
        """
        Select the next token id from model logits.

        Args:
            logits: [batch, vocab] tensor
            state: current GenerationState

        Returns:
            token_id (int)
        """
        raise NotImplementedError

    @abstractmethod
    def should_stop(
        self,
        token_id: int,
        state: GenerationState,
    ) -> bool:
        """
        Determine whether generation should terminate.

        Args:
            token_id: selected token id
            state: current GenerationState

        Returns:
            bool
        """
        raise NotImplementedError