from __future__ import annotations

from abc import ABC, abstractmethod

import pandas as pd

from ..models import Anomaly


class Rule(ABC):
    """Base class for detection rules.

    Subclasses declare class attributes `name`, `topic`, `severity`, then
    implement `detect(df)` which receives the topic-specific DataFrame and
    returns a list of Anomaly instances.
    """

    name: str = "rule"
    topic: str = ""
    severity: str = "warn"

    def __init__(self, subject: str = "AUV000") -> None:
        self.subject = subject

    def bind(self, subject: str) -> "Rule":
        self.subject = subject
        return self

    @abstractmethod
    def detect(self, df: pd.DataFrame) -> list[Anomaly]:
        ...

    def _make(
        self,
        ts: float,
        value: float | None,
        context: dict,
    ) -> Anomaly:
        return Anomaly(
            rule=self.name,
            severity=self.severity,
            timestamp=float(ts),
            subject=self.subject,
            topic=self.topic,
            value=value,
            context=context,
        )