"""A - 近期状态切片: 近 N 场赛果 / 走势(form)。"""
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 Match
from src.llm.slices.common import MatchHeader, SliceResult, _is_stats_available, _outcome

if TYPE_CHECKING:
    from sqlalchemy.ext.asyncio import AsyncSession


async def form_slice(header: MatchHeader, *, limit: int = 5, before=None, db: AsyncSession | None = None) -> SliceResult:
    """A - 近期状态切片: 两队近 N 场赛果、关键事件、走势判断。before=match_date 用于回测。

    db: 可选共享 session,避免每个切片独立建连(见 context_builder 模块 docstring)。
    """
    if db is not None:
        home_form = await _get_form(db, header.home_team_id, before=before, limit=limit)
        away_form = await _get_form(db, header.away_team_id, before=before, limit=limit)
    else:
        async with AsyncSessionLocal() as new_db:
            home_form = await _get_form(new_db, header.home_team_id, before=before, limit=limit)
            away_form = await _get_form(new_db, header.away_team_id, before=before, limit=limit)
    lines = []
    n_scored = 0
    # P0-1 修复:每场历史比赛必须根据「该队当时是主是客」判断 side,
    # 不能用本场 side 硬套 —— 否则客场输球会被算成主场赢球。
    for label, name, form, team_id in (
        ("主队", header.home_name, home_form, header.home_team_id),
        ("客队", header.away_name, away_form, header.away_team_id),
    ):
        lines.append(f"── {label}近况({name},近 {limit} 场) ──")
        if form:
            wins = draws = losses = 0
            for fm in form:
                is_home = (fm.home_team_id == team_id)
                side = "home" if is_home else "away"
                o = _outcome(fm.home_goals, fm.away_goals, side)
                if o == "W": wins += 1
                elif o == "D": draws += 1
                else: losses += 1
                if fm.home_goals is not None:
                    n_scored += 1
                score = f"{fm.home_goals}-{fm.away_goals}" if fm.home_goals is not None else "vs"
                xg = ""
                if fm.stats and _is_stats_available(fm.stats, before) and fm.stats.home_xg is not None:
                    own = fm.stats.home_xg if is_home else fm.stats.away_xg
                    xg = f" (xG {own:.1f})"
                opp = fm.away_team.name if is_home else fm.home_team.name
                lines.append(f"  {o} {score} vs {opp}{xg}")
            lines.append(f"  近 {len(form)} 场: {wins}胜 {draws}平 {losses}负")
        else:
            lines.append("  无数据")
    return SliceResult(text="\n".join(lines), has_data=n_scored > 0, n_records=n_scored)


async def _get_form(db, team_id: int, before, *, limit: int = 5) -> list[Match]:
    """某队近 N 场(已完赛)。before=None 表示不限制(预测赛前的场景由调用方保证)。

    必须预加载 stats / home_team / away_team:切片函数会读取这些关系,
    而 async session 下惰性加载会抛 MissingGreenlet。
    (models.py 已声明 lazy="selectin",此处显式声明以固化查询意图。)
    """
    stmt = (
        select(Match)
        .options(
            selectinload(Match.stats),
            selectinload(Match.home_team),
            selectinload(Match.away_team),
        )
        .where(Match.match_status == "finished")
        .where(Match.score_status == "known")
        .where(Match.home_goals.is_not(None))
        .where((Match.home_team_id == team_id) | (Match.away_team_id == team_id))
        .order_by(Match.match_date.desc())
        .limit(limit)
    )
    if before is not None:
        stmt = stmt.where(Match.match_date < before)
    result = await db.execute(stmt)
    return list(result.scalars().all())