"""System management + record<->system associations.

A System is a per-project, reusable, self-describing subsystem/area. Access is
governed by the project's permission via services/access.py (multi-user ACL
rule) — never a bare owner filter. Records (notes/tasks/issues) link to systems
many-to-many through record_systems, mutable over time.
"""
import logging
from datetime import datetime, timezone

from sqlalchemy import delete, func, select

from scribe.models import async_session
from scribe.models.note import Note
from scribe.models.system import RecordSystem, System
from scribe.services import access

logger = logging.getLogger(__name__)


async def create_system(
    user_id: int,
    project_id: int,
    name: str,
    description: str | None = None,
    color: str | None = None,
    order_index: int = 0,
) -> System | None:
    """Create a System. None if the user can't write the project."""
    if not await access.can_write_project(user_id, project_id):
        return None
    async with async_session() as session:
        system = System(
            user_id=user_id,
            project_id=project_id,
            name=name.strip(),
            description=description,
            color=color,
            order_index=order_index,
        )
        session.add(system)
        await session.commit()
        await session.refresh(system)
        return system


async def get_system(user_id: int, system_id: int) -> System | None:
    """Fetch a System if the user can read its project."""
    async with async_session() as session:
        system = await session.get(System, system_id)
    if system is None or system.deleted_at is not None:
        return None
    if not await access.can_read_project(user_id, system.project_id):
        return None
    return system


async def list_systems(
    user_id: int, project_id: int, include_archived: bool = False
) -> list[System]:
    """A project's systems (active by default). [] if no read access."""
    if not await access.can_read_project(user_id, project_id):
        return []
    async with async_session() as session:
        query = select(System).where(
            System.project_id == project_id,
            System.deleted_at.is_(None),
        )
        if not include_archived:
            query = query.where(System.status == "active")
        query = query.order_by(System.order_index.asc(), System.created_at.asc())
        result = await session.execute(query)
        return list(result.scalars().all())


async def update_system(user_id: int, system_id: int, **fields: object) -> System | None:
    """Update a System if the user can write its project."""
    allowed = {"name", "description", "color", "status", "order_index"}
    async with async_session() as session:
        system = await session.get(System, system_id)
        if system is None or system.deleted_at is not None:
            return None
        if not await access.can_write_project(user_id, system.project_id):
            return None
        for key, value in fields.items():
            if key in allowed 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 archive_system(user_id: int, system_id: int) -> System | None:
    return await update_system(user_id, system_id, status="archived")


async def delete_system(user_id: int, system_id: int) -> bool:
    """Soft-delete a System (recoverable). Requires project write access."""
    async with async_session() as session:
        system = await session.get(System, system_id)
        if system is None or system.deleted_at is not None:
            return False
        if not await access.can_write_project(user_id, system.project_id):
            return False
        system.deleted_at = datetime.now(timezone.utc)
        await session.commit()
        return True


# --- record <-> system associations (many-to-many, mutable) ---

async def set_record_systems(
    user_id: int, note_id: int, system_ids: list[int]
) -> list[int] | None:
    """Replace a record's system associations with `system_ids` (set semantics).

    Returns the resulting associated system ids, or None if the user can't write
    the record. Silently drops ids that don't exist or the user can't read —
    associations only link accessible systems.
    """
    if not await access.can_write_note(user_id, note_id):
        return None
    async with async_session() as session:
        wanted: list[int] = []
        for sid in dict.fromkeys(system_ids):  # de-dup, preserve order
            system = await session.get(System, sid)
            if system is None or system.deleted_at is not None:
                continue
            if not await access.can_read_project(user_id, system.project_id):
                continue
            wanted.append(sid)

        existing = set(
            (
                await session.execute(
                    select(RecordSystem.system_id).where(RecordSystem.note_id == note_id)
                )
            ).scalars().all()
        )
        wanted_set = set(wanted)

        to_remove = existing - wanted_set
        if to_remove:
            await session.execute(
                delete(RecordSystem).where(
                    RecordSystem.note_id == note_id,
                    RecordSystem.system_id.in_(to_remove),
                )
            )
        for sid in wanted:
            if sid not in existing:
                session.add(RecordSystem(note_id=note_id, system_id=sid))
        await session.commit()
        return wanted


async def list_record_systems(user_id: int, note_id: int) -> list[System]:
    """Systems associated with a record (if the user can read it)."""
    if not await access.can_read_note(user_id, note_id):
        return []
    async with async_session() as session:
        result = await session.execute(
            select(System)
            .join(RecordSystem, RecordSystem.system_id == System.id)
            .where(RecordSystem.note_id == note_id, System.deleted_at.is_(None))
            .order_by(System.order_index.asc(), System.name.asc())
        )
        return list(result.scalars().all())


async def list_records_for_system(
    user_id: int, system_id: int, kind: str | None = None, open_only: bool = False
) -> list[Note]:
    """Records associated with a System. `kind` filters task_kind (e.g. 'issue');
    `open_only` limits to tasks not done/cancelled. [] if no read access."""
    system = await get_system(user_id, system_id)
    if system is None:
        return []
    async with async_session() as session:
        query = (
            select(Note)
            .join(RecordSystem, RecordSystem.note_id == Note.id)
            .where(RecordSystem.system_id == system_id, Note.deleted_at.is_(None))
        )
        if kind:
            query = query.where(Note.task_kind == kind)
        if open_only:
            query = query.where(Note.status.not_in(["done", "cancelled"]))
        query = query.order_by(Note.updated_at.desc())
        result = await session.execute(query)
        return list(result.scalars().all())


async def count_open_issues(user_id: int, project_id: int) -> int:
    """Count open (not done/cancelled) issues in a project. 0 if no read access."""
    if not await access.can_read_project(user_id, project_id):
        return 0
    async with async_session() as session:
        result = await session.execute(
            select(func.count(Note.id)).where(
                Note.project_id == project_id,
                Note.task_kind == "issue",
                Note.status.isnot(None),
                Note.status.not_in(["done", "cancelled"]),
                Note.deleted_at.is_(None),
            )
        )
        return int(result.scalar() or 0)


async def open_issue_counts_by_system(user_id: int, project_id: int) -> dict[int, int]:
    """{system_id: open-issue count} for all systems in a project, in one query.
    {} if no read access."""
    if not await access.can_read_project(user_id, project_id):
        return {}
    async with async_session() as session:
        rows = await session.execute(
            select(RecordSystem.system_id, func.count(Note.id))
            .join(Note, Note.id == RecordSystem.note_id)
            .join(System, System.id == RecordSystem.system_id)
            .where(
                System.project_id == project_id,
                Note.task_kind == "issue",
                Note.status.isnot(None),
                Note.status.not_in(["done", "cancelled"]),
                Note.deleted_at.is_(None),
            )
            .group_by(RecordSystem.system_id)
        )
        return {sid: cnt for sid, cnt in rows.fetchall()}


async def list_issues(user_id: int, project_id: int, open_only: bool = True) -> list[Note]:
    """Issues in a project (open by default), newest first. [] if no read access."""
    if not await access.can_read_project(user_id, project_id):
        return []
    async with async_session() as session:
        query = select(Note).where(
            Note.project_id == project_id,
            Note.task_kind == "issue",
            Note.status.isnot(None),
            Note.deleted_at.is_(None),
        )
        if open_only:
            query = query.where(Note.status.not_in(["done", "cancelled"]))
        query = query.order_by(Note.updated_at.desc())
        result = await session.execute(query)
        return list(result.scalars().all())