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backend/app/services/boxes.py

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+import uuid
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import selectinload
+
+from app.models.box import Box
+from app.schemas.box import BoxCreate, BoxRead, BoxSummary, BoxUpdate
+from app.schemas.object import ObjectSummary
+from app.services.qrcodes import box_public_url
+
+
+def _select_with_relations():
+    return select(Box).options(selectinload(Box.children), selectinload(Box.objects))
+
+
+async def list_boxes(
+    db: AsyncSession, search: str | None = None, root_only: bool = False
+) -> list[Box]:
+    stmt = select(Box).order_by(Box.name)
+    if root_only:
+        stmt = stmt.where(Box.parent_box_id.is_(None))
+    if search:
+        stmt = stmt.where(Box.name.ilike(f"%{search}%"))
+    result = await db.execute(stmt)
+    return list(result.scalars().all())
+
+
+async def get_box(db: AsyncSession, box_id: uuid.UUID) -> Box | None:
+    stmt = _select_with_relations().where(Box.id == box_id)
+    result = await db.execute(stmt)
+    return result.scalar_one_or_none()
+
+
+async def build_box_read(db: AsyncSession, box: Box) -> BoxRead:
+    ancestors: list[BoxSummary] = []
+    current_parent_id = box.parent_box_id
+    depth = 0
+    while current_parent_id is not None and depth < 100:
+        parent = await db.get(Box, current_parent_id)
+        if parent is None:
+            break
+        ancestors.append(BoxSummary(id=parent.id, name=parent.name))
+        current_parent_id = parent.parent_box_id
+        depth += 1
+    ancestors.reverse()
+
+    return BoxRead(
+        id=box.id,
+        name=box.name,
+        description=box.description,
+        parent_box_id=box.parent_box_id,
+        created_at=box.created_at,
+        updated_at=box.updated_at,
+        qr_code_url=box_public_url(box.id),
+        ancestors=ancestors,
+        children=[BoxSummary.model_validate(c) for c in box.children],
+        objects=[ObjectSummary.model_validate(o) for o in box.objects],
+    )
+
+
+async def _is_descendant(db: AsyncSession, box_id: uuid.UUID, candidate_ancestor_id: uuid.UUID) -> bool:
+    """Whether candidate_ancestor_id is box_id itself or one of its descendants."""
+    if box_id == candidate_ancestor_id:
+        return True
+    stmt = select(Box.id).where(Box.parent_box_id == box_id)
+    result = await db.execute(stmt)
+    for child_id in result.scalars().all():
+        if await _is_descendant(db, child_id, candidate_ancestor_id):
+            return True
+    return False
+
+
+async def create_box(db: AsyncSession, data: BoxCreate) -> Box:
+    box = Box(**data.model_dump())
+    db.add(box)
+    await db.commit()
+    return await get_box(db, box.id)
+
+
+async def update_box(db: AsyncSession, box: Box, data: BoxUpdate) -> Box:
+    updates = data.model_dump(exclude_unset=True)
+    new_parent_id = updates.get("parent_box_id", box.parent_box_id)
+    if new_parent_id is not None and await _is_descendant(db, box.id, new_parent_id):
+        raise ValueError("A box cannot be moved into itself or one of its own descendants")
+    for field, value in updates.items():
+        setattr(box, field, value)
+    await db.commit()
+    return await get_box(db, box.id)
+
+
+async def delete_box(db: AsyncSession, box: Box) -> None:
+    child_count = await db.scalar(select(Box.id).where(Box.parent_box_id == box.id).limit(1))
+    if child_count is not None:
+        raise ValueError("Cannot delete a box that still contains nested boxes")
+    await db.delete(box)
+    await db.commit()