"""Read-only baseline comparison over explicit local Alpha and PnL snapshots."""

import math

from fastapi import HTTPException

from ..models import Alpha, Pnl
from .serialization import encode_snapshot as jsonable_encoder


async def compare(db, alpha_ids):
    if len(set(alpha_ids)) != len(alpha_ids):
        raise HTTPException(422, "比较项不能重复")
    rows, by_id = [], {}
    for alpha_id in alpha_ids:
        alpha = await db.get(Alpha, alpha_id)
        if not alpha:
            raise HTTPException(404, f"Alpha {alpha_id} 尚未同步")
        pnl = await db.get(Pnl, alpha_id)
        by_id[alpha_id] = (
            {
                p["date"][:10]: p["value"]
                for p in pnl.points
                if type(p.get("value")) in (int, float) and math.isfinite(p["value"])
            }
            if pnl
            else {}
        )
        rows.append(
            {
                "alpha_id": alpha.id,
                "expression": alpha.expression,
                "settings": alpha.settings,
                "metrics": alpha.is_metrics,
                "observed_at": alpha.synced_at,
                "pnl_fetched_at": pnl.fetched_at if pnl else None,
            }
        )
    common = sorted(set.intersection(*(set(points) for points in by_id.values())))
    for row in rows:
        points = by_id[row["alpha_id"]]
        row["pnl"] = [{"date": date, "value": points[date] - points[common[0]]} for date in common]
    return jsonable_encoder(
        {
            "baseline_alpha_id": alpha_ids[0],
            "items": rows,
            "common_dates": common,
            "window": {"from": common[0], "to": common[-1]} if common else None,
            "different_settings": any(row["settings"] != rows[0]["settings"] for row in rows[1:]),
            "note": "PnL 按共同日期展示并从窗口起点归零；缓存缺失时请在 Alpha 详情获取 PnL",
        }
    )