"""Background poller that maintains live game-server state in the DB.

Modeled on l4d2web/services/job_worker.py:617-647. This module owns:
  - per-server snapshot writes with run-length encoding into
    `server_live_state`
  - player-session lifecycle in `server_player_session` (Task 7)
  - Steam profile enrichment into `steam_user_profile` (Task 8)
  - retention pruning and stuck-session closure (Task 10)

This file is built up across Tasks 6-10.
"""
from __future__ import annotations

import logging
from datetime import datetime, timedelta, UTC

from sqlalchemy import select

from l4d2web.db import session_scope
from l4d2web.models import (
    Server,
    ServerLiveState,
    ServerPlayerSession,
)
from l4d2web.services.rcon import RconError, StatusResponse, query_status


logger = logging.getLogger(__name__)


def _now() -> datetime:
    return datetime.now(UTC).replace(tzinfo=None)


def poll_once() -> None:
    """One pass over all running servers with a configured rcon_password."""
    with session_scope() as db:
        servers = db.scalars(
            select(Server)
            .where(Server.actual_state == "running")
            .where(Server.rcon_password != "")
        ).all()
        targets = [(s.id, s.port, s.rcon_password) for s in servers]

    for server_id, port, password in targets:
        try:
            status = query_status("127.0.0.1", port, password, timeout=2.0)
        except RconError:
            logger.warning("rcon query failed for server %d", server_id, exc_info=True)
            continue

        _record_snapshot(server_id, status)
        _reconcile_sessions(server_id, status)


def _record_snapshot(server_id: int, status: StatusResponse) -> None:
    """RLE write: bump last_seen_at if state matches, else insert a new row."""
    now = _now()
    with session_scope() as db:
        latest = db.scalars(
            select(ServerLiveState)
            .where(ServerLiveState.server_id == server_id)
            .order_by(ServerLiveState.started_at.desc())
            .limit(1)
        ).first()

        if latest is not None and _matches(latest, status):
            latest.last_seen_at = now
            return

        db.add(
            ServerLiveState(
                server_id=server_id,
                started_at=now,
                last_seen_at=now,
                players=status.players,
                max_players=status.max_players,
                bots=status.bots,
                map=status.map,
                hibernating=status.hibernating,
            )
        )


def _matches(row: ServerLiveState, status: StatusResponse) -> bool:
    return (
        row.players == status.players
        and row.max_players == status.max_players
        and row.bots == status.bots
        and row.map == status.map
        and row.hibernating == status.hibernating
    )


_STEAM_ID_64_PREFIX = "7656"  # all SteamID64s start with this; bots/anon do not


def _is_valid_steam_id_64(value: str) -> bool:
    return value.startswith(_STEAM_ID_64_PREFIX) and value.isdigit() and len(value) == 17


def _reconcile_sessions(server_id: int, status: StatusResponse) -> None:
    """Open new sessions, update ping ranges, close departed sessions."""
    now = _now()
    roster = [p for p in status.roster if _is_valid_steam_id_64(p.steam_id_64)]
    seen_ids = {p.steam_id_64 for p in roster}

    with session_scope() as db:
        open_rows = db.scalars(
            select(ServerPlayerSession).where(
                ServerPlayerSession.server_id == server_id,
                ServerPlayerSession.left_at.is_(None),
            )
        ).all()
        open_by_sid = {r.steam_id_64: r for r in open_rows}

        # Close sessions for players no longer in the roster.
        for sid, row in open_by_sid.items():
            if sid not in seen_ids:
                row.left_at = now

        # Open / update sessions for current roster.
        for p in roster:
            existing = open_by_sid.get(p.steam_id_64)
            if existing is None:
                db.add(
                    ServerPlayerSession(
                        server_id=server_id,
                        steam_id_64=p.steam_id_64,
                        joined_at=now - timedelta(seconds=p.connected_seconds),
                        left_at=None,
                        name_at_join=p.name,
                        min_ping=p.ping,
                        max_ping=p.ping,
                    )
                )
            else:
                if p.ping < existing.min_ping:
                    existing.min_ping = p.ping
                if p.ping > existing.max_ping:
                    existing.max_ping = p.ping