from sqlalchemy import func, select, update

from api.db.connection import SessionLocal
from api.models.section import Section
from api.models.video import Video


async def list_sections() -> list[dict]:
    """Плоский список разделов + количество видео в каждом (дерево строит клиент)."""
    async with SessionLocal() as session:
        res = await session.execute(select(Section).order_by(Section.name))
        sections = list(res.scalars().all())
        counts_res = await session.execute(
            select(Video.section_id, func.count()).group_by(Video.section_id)
        )
        counts = dict(counts_res.all())
        return [
            {
                "id": s.id,
                "name": s.name,
                "parent_id": s.parent_id,
                "video_count": counts.get(s.id, 0),
            }
            for s in sections
        ]


async def create_section(name: str, parent_id: int | None) -> Section:
    async with SessionLocal() as session:
        if parent_id is not None:
            parent = await session.get(Section, parent_id)
            if parent is None:
                raise ValueError(f"Parent section {parent_id} not found")
        s = Section(name=name, parent_id=parent_id)
        session.add(s)
        await session.commit()
        await session.refresh(s)
        return s


async def delete_section(section_id: int) -> bool:
    """Удаляет раздел: дочерние разделы поднимаются к родителю, видео — без раздела."""
    async with SessionLocal() as session:
        s = await session.get(Section, section_id)
        if s is None:
            return False
        await session.execute(
            update(Section)
            .where(Section.parent_id == section_id)
            .values(parent_id=s.parent_id)
        )
        await session.execute(
            update(Video).where(Video.section_id == section_id).values(section_id=None)
        )
        await session.delete(s)
        await session.commit()
        return True