from abc import ABC, abstractmethod
from dataclasses import dataclass


@dataclass
class Reading:
    """A single normalized vital reading."""
    source_type: str        # "renpho", "garmin", etc.
    source_user_id: str     # user identifier within source
    metric: str             # "weight", "body_fat", "bmi", etc.
    value: float
    unit: str               # "kg", "%", "bpm", etc.
    timestamp: int          # unix seconds


class Source(ABC):
    """Base class for health data source adapters."""

    @abstractmethod
    async def fetch(self) -> list[Reading]:
        """Authenticate if needed, fetch measurements, return normalized readings."""
        ...