"""Build nested category tree from global_tree_category."""
from __future__ import annotations

from typing import Any

from supply_infra.db.models.global_tree_category import GlobalTreeCategory
from supply_infra.db.repositories.global_tree_category_repo import GlobalTreeCategoryRepository
from supply_infra.db.session import get_session


def _normalize_parent_id(parent_id: int | None) -> int | None:
    if parent_id is None or parent_id == 0:
        return None
    return parent_id


def _build_children_map(
    categories: list[GlobalTreeCategory],
) -> dict[int | None, list[GlobalTreeCategory]]:
    children_map: dict[int | None, list[GlobalTreeCategory]] = {}
    for category in categories:
        parent_key = _normalize_parent_id(category.parent_id)
        children_map.setdefault(parent_key, []).append(category)

    for children in children_map.values():
        children.sort(key=lambda c: (c.level or 0, c.id))

    return children_map


def _to_node(
    category: GlobalTreeCategory,
    children_map: dict[int | None, list[GlobalTreeCategory]],
) -> dict[str, Any]:
    children = [
        _to_node(child, children_map) for child in children_map.get(category.id, [])
    ]
    return {
        "id": category.id,
        "name": category.name,
        "level": category.level,
        "description": category.description,
        "children": children,
    }


def build_category_tree() -> list[dict[str, Any]]:
    """Load all active categories and return nested root nodes."""
    with get_session() as session:
        repo = GlobalTreeCategoryRepository(session)
        categories = repo.list_active_categories()
        # Build JSON while session is open to avoid DetachedInstanceError.
        children_map = _build_children_map(categories)
        return [_to_node(root, children_map) for root in children_map.get(None, [])]