"""D - 联赛排名切片: 积分榜快照(支持 cutoff 的历史还原,standings)。"""
from __future__ import annotations

from typing import TYPE_CHECKING

from sqlalchemy import select
from sqlalchemy.orm import selectinload

from src.db.base import AsyncSessionLocal
from src.db.models import League, Standing
from src.llm.slices.common import MatchHeader, SliceResult

if TYPE_CHECKING:
    from sqlalchemy.ext.asyncio import AsyncSession


async def standings_slice(header: MatchHeader, *, before=None, db: AsyncSession | None = None) -> SliceResult:
    """D - 联赛排名切片: 两队积分榜位置、积分、近期走势(form)、分区,评估整体实力差距。

    P0-02: 支持 cutoff(before)。取 available_at<=cutoff 的每队最新快照
    (DISTINCT ON team_id ORDER available_at DESC);before=None 时 cutoff=now()。
    回测时可还原历史时刻榜单,不再只是"最新快照、忽略 cutoff"。

    db: 可选共享 session(见 context_builder 模块 docstring)。

    语义区分:
      - 两队都有积分榜行 → has_data=True(明确的排名信息)
      - 任一队缺失 → has_data=False(升班马/杯赛无榜,信息不完整时明确声明)
    """
    # P0-02: before=None → cutoff=now()(取最新可用快照)
    if before is None:
        from datetime import datetime, timezone
        before = datetime.now(timezone.utc)

    if db is not None:
        league = (await db.execute(select(League).where(League.id == header.league_id))).scalar_one_or_none()
        # P0-02: DISTINCT ON (team_id) 取 available_at<=cutoff 的最新快照
        rows = (
            (
                await db.execute(
                    select(Standing)
                    .options(selectinload(Standing.team))
                    .where(Standing.league_id == header.league_id)
                    .where(Standing.available_at <= before)
                    .distinct(Standing.team_id)
                    .order_by(Standing.team_id, Standing.available_at.desc())
                )
            )
            .scalars()
            .all()
            if league
            else []
        )
    else:
        async with AsyncSessionLocal() as new_db:
            return await standings_slice(header, before=before, db=new_db)

    lines = [f"── 联赛排名({header.league_name} 共 {len(rows)} 队) ──"]
    n_records = 0

    def _fmt(row) -> str:
        zg = f" xG差 {row.xg_for - row.xg_against:+.1f}" if row.xg_for is not None and row.xg_against is not None else ""
        form = f" 近5场 {row.form}" if row.form else ""
        zone = f" [{row.zone}]" if row.zone else ""
        return (
            f"    第 {row.position} 名: {row.points} 分 / {row.played} 场 "
            f"({row.won}胜{row.drawn}平{row.lost}负, 进{row.goals_for}失{row.goals_against} 净胜{row.goal_diff:+d}"
            f"{zg}){form}{zone}"
        )

    for label, team_id in (("主队", header.home_team_id), ("客队", header.away_team_id)):
        row = next((r for r in rows if r.team_id == team_id), None)
        if row is None:
            lines.append(f"  {label}: 暂无积分榜数据(可能杯赛/赛季未开始)")
        else:
            n_records += 1
            lines.append(f"  {label} {header.home_name if label == '主队' else header.away_name}:")
            lines.append(_fmt(row))

    # 两队排名对比摘要
    home_row = next((r for r in rows if r.team_id == header.home_team_id), None)
    away_row = next((r for r in rows if r.team_id == header.away_team_id), None)
    if home_row and away_row:
        diff = home_row.position - away_row.position  # 正数=主队排名更靠前(名次更小)
        lead = f"主队排名高 {diff} 位" if diff > 0 else (f"客队排名高 {-diff} 位" if diff < 0 else "两队同排名结构")
        pts_diff = home_row.points - away_row.points
        lines.append(f"  排名对比: {lead}, 分差 {pts_diff:+d}")

    # has_data: 两队都有行才算完整;只有一队时仍有价值,但标记不完整
    has_data = n_records >= 1
    return SliceResult(text="\n".join(lines), has_data=has_data, n_records=n_records)