from __future__ import annotations

from sqlalchemy import select, func
from sqlalchemy.ext.asyncio import AsyncSession

from shared.events import emit_event
from shared.models.container_relation import ContainerRelation


async def attach_child(
    session: AsyncSession,
    parent_type: str,
    parent_id: int,
    child_type: str,
    child_id: int,
    label: str | None = None,
    sort_order: int | None = None,
) -> ContainerRelation:
    """
    Create a ContainerRelation and emit container.child_attached event.

    Upsert behaviour: if a relation already exists (including soft-deleted),
    revive it instead of inserting a duplicate.
    """
    # Check for existing (including soft-deleted)
    existing = await session.scalar(
        select(ContainerRelation).where(
            ContainerRelation.parent_type == parent_type,
            ContainerRelation.parent_id == parent_id,
            ContainerRelation.child_type == child_type,
            ContainerRelation.child_id == child_id,
        )
    )
    if existing:
        if existing.deleted_at is not None:
            # Revive soft-deleted relation
            existing.deleted_at = None
            if sort_order is not None:
                existing.sort_order = sort_order
            if label is not None:
                existing.label = label
            await session.flush()
            await emit_event(
                session,
                event_type="container.child_attached",
                aggregate_type="container_relation",
                aggregate_id=existing.id,
                payload={
                    "parent_type": parent_type,
                    "parent_id": parent_id,
                    "child_type": child_type,
                    "child_id": child_id,
                },
            )
            return existing
        # Already attached and active — no-op
        return existing

    if sort_order is None:
        max_order = await session.scalar(
            select(func.max(ContainerRelation.sort_order)).where(
                ContainerRelation.parent_type == parent_type,
                ContainerRelation.parent_id == parent_id,
                ContainerRelation.deleted_at.is_(None),
            )
        )
        sort_order = (max_order or 0) + 1

    rel = ContainerRelation(
        parent_type=parent_type,
        parent_id=parent_id,
        child_type=child_type,
        child_id=child_id,
        label=label,
        sort_order=sort_order,
    )
    session.add(rel)
    await session.flush()

    await emit_event(
        session,
        event_type="container.child_attached",
        aggregate_type="container_relation",
        aggregate_id=rel.id,
        payload={
            "parent_type": parent_type,
            "parent_id": parent_id,
            "child_type": child_type,
            "child_id": child_id,
        },
    )

    return rel


async def get_children(
    session: AsyncSession,
    parent_type: str,
    parent_id: int,
    child_type: str | None = None,
) -> list[ContainerRelation]:
    """Query children of a container, optionally filtered by child_type."""
    stmt = select(ContainerRelation).where(
        ContainerRelation.parent_type == parent_type,
        ContainerRelation.parent_id == parent_id,
        ContainerRelation.deleted_at.is_(None),
    )
    if child_type is not None:
        stmt = stmt.where(ContainerRelation.child_type == child_type)

    stmt = stmt.order_by(
        ContainerRelation.sort_order.asc(), ContainerRelation.id.asc()
    )
    result = await session.execute(stmt)
    return list(result.scalars().all())


async def detach_child(
    session: AsyncSession,
    parent_type: str,
    parent_id: int,
    child_type: str,
    child_id: int,
) -> bool:
    """Soft-delete a ContainerRelation and emit container.child_detached event."""
    result = await session.execute(
        select(ContainerRelation).where(
            ContainerRelation.parent_type == parent_type,
            ContainerRelation.parent_id == parent_id,
            ContainerRelation.child_type == child_type,
            ContainerRelation.child_id == child_id,
            ContainerRelation.deleted_at.is_(None),
        )
    )
    rel = result.scalar_one_or_none()
    if not rel:
        return False

    rel.deleted_at = func.now()
    await session.flush()

    await emit_event(
        session,
        event_type="container.child_detached",
        aggregate_type="container_relation",
        aggregate_id=rel.id,
        payload={
            "parent_type": parent_type,
            "parent_id": parent_id,
            "child_type": child_type,
            "child_id": child_id,
        },
    )

    return True