"""State machine треда: текущая ветка, шаг внутри ветки, собранные слоты.

Используется в chat_service для ведения многошаговых сценариев (Спринт 5).
Слоты — произвольный JSON-словарь, конкретные ключи определяются веткой.
"""
import json
import logging
from datetime import datetime, timezone

from sqlalchemy.ext.asyncio import AsyncSession

from db.models import ThreadState

logger = logging.getLogger(__name__)


async def get_state(session: AsyncSession, thread_id: int) -> ThreadState | None:
    return await session.get(ThreadState, thread_id)


def _parse_slots(raw: str) -> dict:
    if not raw:
        return {}
    try:
        value = json.loads(raw)
    except json.JSONDecodeError:
        logger.warning("Bad slots_json for thread_state, resetting to {}")
        return {}
    return value if isinstance(value, dict) else {}


async def load_snapshot(session: AsyncSession, thread_id: int) -> dict:
    """Снимок состояния диалога: текущая ветка/шаг/слоты + handoff_count + suspended_*."""
    state = await get_state(session, thread_id)
    if state is None:
        return {
            "current_intent_code": None,
            "current_step": 0,
            "current_step_code": None,
            "slots": {},
            "handoff_count": 0,
            "soft_insertion_count": 0,
            "suspended_intent": None,
            "resumable_step_code": None,
            "resumable_slots": {},
        }
    resumable_slots = {}
    if state.resumable_slots_json:
        try:
            value = json.loads(state.resumable_slots_json)
            if isinstance(value, dict):
                resumable_slots = value
        except json.JSONDecodeError:
            logger.warning("Bad resumable_slots_json for thread_state, ignoring")
    return {
        "current_intent_code": state.current_intent_code,
        "current_step": state.current_step,
        "current_step_code": state.current_step_code,
        "slots": _parse_slots(state.slots_json),
        "handoff_count": state.handoff_count,
        "soft_insertion_count": state.soft_insertion_count,
        "suspended_intent": state.suspended_intent,
        "resumable_step_code": state.resumable_step_code,
        "resumable_slots": resumable_slots,
    }


async def upsert(
    session: AsyncSession,
    thread_id: int,
    *,
    intent_code: str | None,
    step: int,
    slots: dict,
    step_code: str | None = None,
    handoff_count: int = 0,
    soft_insertion_count: int = 0,
    suspended_intent: str | None = None,
    resumable_step_code: str | None = None,
    resumable_slots: dict | None = None,
) -> ThreadState:
    """Создать или обновить состояние треда. Коммит — на совести вызывающего."""
    state = await get_state(session, thread_id)
    now = datetime.now(timezone.utc)
    slots_raw = json.dumps(slots or {}, ensure_ascii=False)
    resumable_raw = (
        json.dumps(resumable_slots, ensure_ascii=False)
        if resumable_slots is not None and len(resumable_slots) > 0
        else None
    )
    if state is None:
        state = ThreadState(
            thread_id=thread_id,
            current_intent_code=intent_code,
            current_step=step,
            current_step_code=step_code,
            slots_json=slots_raw,
            handoff_count=handoff_count,
            soft_insertion_count=soft_insertion_count,
            suspended_intent=suspended_intent,
            resumable_step_code=resumable_step_code,
            resumable_slots_json=resumable_raw,
            updated_at=now,
        )
        session.add(state)
    else:
        state.current_intent_code = intent_code
        state.current_step = step
        state.current_step_code = step_code
        state.slots_json = slots_raw
        state.handoff_count = handoff_count
        state.soft_insertion_count = soft_insertion_count
        state.suspended_intent = suspended_intent
        state.resumable_step_code = resumable_step_code
        state.resumable_slots_json = resumable_raw
        state.updated_at = now
    return state


async def reset(
    session: AsyncSession,
    thread_id: int,
    *,
    new_intent_code: str | None,
    new_step_code: str | None = None,
) -> ThreadState:
    """Сбросить шаг и слоты треда, выставить новую ветку (при смене intent)."""
    return await upsert(
        session, thread_id,
        intent_code=new_intent_code, step=0, step_code=new_step_code, slots={},
        handoff_count=0,
    )