"""Design system + token persistence, and the guard on the parent chain.

Access goes through `services/access.py` (rule #78), where reaching a system via
a project you can see grants READ but never write — see
`get_design_system_permission` for why that asymmetry exists.

The cascade itself lives in `services/design_cascade.py` as pure functions. This
module is the part that needs a database: loading the shape of the hierarchy,
refusing writes that would break it, and storing tokens.

Nothing here seeds or implies a default system. An install with no design
systems is an ordinary install, and every caller must handle an empty list as
the normal case rather than a missing prerequisite.
"""
import logging
from datetime import datetime, timezone

from sqlalchemy import select

from scribe.models import async_session
from scribe.models.design_system import DesignSystem, DesignToken
from scribe.models.project import Project
from scribe.services import access
from scribe.services.design_cascade import (
    ResolvedToken,
    ancestry,
    resolve_tokens,
    would_cycle,
)

logger = logging.getLogger(__name__)


class DesignSystemCycle(ValueError):
    """A parent assignment that would close an inheritance loop.

    Raised rather than returned as None because the two outcomes need different
    answers: None already means "not found, or not yours", and a caller that
    conflated them would show "no such design system" for what is really "that
    parent is one of its own descendants". Routes map this to a 400.
    """


async def _parent_map(session, owner_user_id: int) -> dict[int, int | None]:
    """`{id: parent_id}` for one owner's live systems — the hierarchy's shape.

    Scoped to the OWNER of the systems, not the caller, and the distinction is
    load-bearing on the read path: a caller reading through a shared project
    does not own any link in the chain, and a caller-scoped map would hand them
    an empty forest and a cascade truncated to one system. They would get a page
    that renders with plausible wrong values and no error anywhere.

    Owner-scoping is also the constraint on parenting: a chain may only be built
    from systems its owner controls, or someone else's delete or re-parent would
    silently restyle your app.
    """
    rows = (
        await session.execute(
            select(DesignSystem.id, DesignSystem.parent_id).where(
                DesignSystem.owner_user_id == owner_user_id,
                DesignSystem.deleted_at.is_(None),
            )
        )
    ).all()
    return dict(rows)


# --- design systems ---------------------------------------------------------

async def create_design_system(
    user_id: int,
    title: str,
    description: str | None = None,
    parent_id: int | None = None,
) -> DesignSystem | None:
    """Create a system, with or without a parent.

    Returns None when `parent_id` names a system the caller may not write —
    which, per the ACL, means one they do not own.
    """
    if parent_id is not None and not await access.can_write_design_system(
        user_id, parent_id
    ):
        return None
    async with async_session() as session:
        system = DesignSystem(
            owner_user_id=user_id,
            title=title.strip(),
            description=description,
            parent_id=parent_id,
        )
        session.add(system)
        await session.commit()
        await session.refresh(system)
        return system


async def get_design_system(user_id: int, design_system_id: int) -> DesignSystem | None:
    async with async_session() as session:
        system = await session.get(DesignSystem, design_system_id)
    if system is None or system.deleted_at is not None:
        return None
    if not await access.can_read_design_system(user_id, design_system_id):
        return None
    return system


async def list_design_systems(user_id: int) -> list[DesignSystem]:
    """The caller's own systems, ordered by title. Empty is normal."""
    async with async_session() as session:
        rows = await session.execute(
            select(DesignSystem)
            .where(
                DesignSystem.owner_user_id == user_id,
                DesignSystem.deleted_at.is_(None),
            )
            .order_by(DesignSystem.title)
        )
        return list(rows.scalars().all())


async def update_design_system(
    user_id: int, design_system_id: int, **fields: object
) -> DesignSystem | None:
    """Partial update. Raises DesignSystemCycle if `parent_id` would loop.

    `parent_id` is handled apart from the other fields because None is a
    meaningful value for it — "make this a root" — where for every other field
    None means "leave alone". Callers signal it by passing the key at all.
    """
    if not await access.can_write_design_system(user_id, design_system_id):
        return None
    async with async_session() as session:
        system = await session.get(DesignSystem, design_system_id)
        if system is None or system.deleted_at is not None:
            return None

        if "parent_id" in fields:
            parent_id = fields.pop("parent_id")
            if parent_id is not None:
                parent_id = int(parent_id)
                if not await access.can_write_design_system(user_id, parent_id):
                    return None
            if would_cycle(
                design_system_id,
                parent_id,
                await _parent_map(session, system.owner_user_id),
            ):
                raise DesignSystemCycle(
                    f"Design system {design_system_id} cannot inherit from "
                    f"{parent_id}: that system already inherits from it."
                )
            system.parent_id = parent_id

        for key, value in fields.items():
            if key in ("title", "description") and value is not None:
                setattr(system, key, value)
        system.updated_at = datetime.now(timezone.utc)
        await session.commit()
        await session.refresh(system)
        return system


async def delete_design_system(user_id: int, design_system_id: int) -> bool:
    """Soft-delete a system. Children survive as roots (the FK is SET NULL)."""
    if not await access.can_write_design_system(user_id, design_system_id):
        return False
    async with async_session() as session:
        system = await session.get(DesignSystem, design_system_id)
        if system is None or system.deleted_at is not None:
            return False
        system.deleted_at = datetime.now(timezone.utc)
        await session.commit()
        return True


# --- tokens -----------------------------------------------------------------

async def create_token(
    user_id: int,
    design_system_id: int,
    name: str,
    value_by_mode: dict | None = None,
    group_name: str | None = None,
    purpose: str | None = None,
    order_index: int = 0,
) -> DesignToken | None:
    if not await access.can_write_design_system(user_id, design_system_id):
        return None
    async with async_session() as session:
        token = DesignToken(
            design_system_id=design_system_id,
            name=name.strip(),
            # `or {}` and not the argument as given: the column is NOT NULL so
            # that absence has exactly one spelling. Passing None here would
            # otherwise store JSON null and reintroduce the second empty state.
            value_by_mode=value_by_mode or {},
            group_name=group_name,
            purpose=purpose,
            order_index=order_index,
        )
        session.add(token)
        await session.commit()
        await session.refresh(token)
        return token


async def list_tokens(user_id: int, design_system_id: int) -> list[DesignToken]:
    """One system's OWN tokens — its override set, not its effective set.

    Resolving the chain is step 2's job; this deliberately answers the narrower
    question ("what does this system change?") that the model exists to make
    free.
    """
    if not await access.can_read_design_system(user_id, design_system_id):
        return []
    async with async_session() as session:
        rows = await session.execute(
            select(DesignToken)
            .where(
                DesignToken.design_system_id == design_system_id,
                DesignToken.deleted_at.is_(None),
            )
            .order_by(DesignToken.order_index.asc(), DesignToken.name.asc())
        )
        return list(rows.scalars().all())


async def resolve_design_system(
    user_id: int, design_system_id: int
) -> list[ResolvedToken] | None:
    """A system's EFFECTIVE token set — everything it inherits, with its own on top.

    None when the caller may not read the system; an empty list when the chain
    genuinely holds no tokens, which is an ordinary state for a system that has
    just been created.

    Two queries regardless of how deep the chain runs: one for the hierarchy's
    shape, one for every token in it. The flattening itself is
    `design_cascade.resolve_tokens` — pure, so the cascade rule is tested
    without a database and this function is only the loading.
    """
    if not await access.can_read_design_system(user_id, design_system_id):
        return None
    async with async_session() as session:
        system = await session.get(DesignSystem, design_system_id)
        if system is None or system.deleted_at is not None:
            return None

        parents = await _parent_map(session, system.owner_user_id)
        chain = ancestry(design_system_id, parents)

        rows = (
            await session.execute(
                select(DesignToken)
                .where(
                    DesignToken.design_system_id.in_(chain),
                    DesignToken.deleted_at.is_(None),
                )
                .order_by(DesignToken.order_index.asc(), DesignToken.name.asc())
            )
        ).scalars().all()

    tokens_by_system: dict[int, list[DesignToken]] = {}
    for token in rows:
        tokens_by_system.setdefault(token.design_system_id, []).append(token)
    return resolve_tokens(design_system_id, parents, tokens_by_system)


async def update_token(
    user_id: int, token_id: int, **fields: object
) -> DesignToken | None:
    allowed = {"name", "value_by_mode", "group_name", "purpose", "order_index"}
    async with async_session() as session:
        token = await session.get(DesignToken, token_id)
        if token is None or token.deleted_at is not None:
            return None
        if not await access.can_write_design_system(user_id, token.design_system_id):
            return None
        for key, value in fields.items():
            if key in allowed and value is not None:
                setattr(token, key, value)
        token.updated_at = datetime.now(timezone.utc)
        await session.commit()
        await session.refresh(token)
        return token


async def delete_token(user_id: int, token_id: int) -> bool:
    async with async_session() as session:
        token = await session.get(DesignToken, token_id)
        if token is None or token.deleted_at is not None:
            return False
        if not await access.can_write_design_system(user_id, token.design_system_id):
            return False
        token.deleted_at = datetime.now(timezone.utc)
        await session.commit()
        return True


# --- the project pointer ----------------------------------------------------

async def set_project_design_system(
    user_id: int, project_id: int, design_system_id: int | None
) -> bool:
    """Point a project at a design system, or at nothing (None clears it).

    Needs write on the project and READ on the system: pointing at a system is
    consuming it, not changing it, so a system shared with you through another
    project is a legitimate choice here.
    """
    if not await access.can_write_project(user_id, project_id):
        return False
    if design_system_id is not None and not await access.can_read_design_system(
        user_id, design_system_id
    ):
        return False
    async with async_session() as session:
        project = await session.get(Project, project_id)
        if project is None or project.deleted_at is not None:
            return False
        project.design_system_id = design_system_id
        project.updated_at = datetime.now(timezone.utc)
        await session.commit()
        return True