from typing import List
from sqlalchemy.inspection import inspect
from sqlalchemy.orm import Load, joinedload, selectinload

def default_eager_policy(Model, expand: List[str]) -> List[Load]:
    """
    Heuristic:
      - many-to-one / one-to-one: joinedload
      - one-to-many / many-to-many: selectinload
    Accepts dotted paths like "author.publisher".
    """
    if not expand:
        return []

    opts: List[Load] = []

    for path in expand:
        parts = path.split(".")
        current_model = Model
        current_inspect = inspect(current_model)

        # first hop
        rel = current_inspect.relationships.get(parts[0])
        if not rel:
            continue  # silently skip bad names
        attr = getattr(current_model, parts[0])
        loader: Load = selectinload(attr) if rel.uselist else joinedload(attr)
        current_model = rel.mapper.class_

        # nested hops, if any
        for name in parts[1:]:
            current_inspect = inspect(current_model)
            rel = current_inspect.relationships.get(name)
            if not rel:
                break
            attr = getattr(current_model, name)
            loader = loader.selectinload(attr) if rel.uselist else loader.joinedload(attr)
            current_model = rel.mapper.class_

        opts.append(loader)

    return opts