"""时间衰减：招聘数据存在时滞，越旧的 JD 对当前能力刻画的贡献越低。

权重公式：w = exp(-λ · age)，age 为发布日期距参考日期的年数。
"""
from __future__ import annotations

import logging
import math
from datetime import date

from app.models import JDRecord

logger = logging.getLogger(__name__)


def decay_weight(publish_date: date, ref_date: date, lam: float = 0.35) -> float:
    """计算单条 JD 的时间衰减权重。"""
    age_years = max(0.0, (ref_date - publish_date).days / 365.25)
    return round(math.exp(-lam * age_years), 4)


def apply_decay(
    records: list[JDRecord],
    ref_date: date | None = None,
    lam: float = 0.35,
) -> list[JDRecord]:
    """就地更新每条记录的 weight（与已有降权相乘，不会覆盖抄袭降权）。"""
    if ref_date is None:
        ref_date = max((r.publish_date for r in records), default=date.today())
    for r in records:
        r.weight = round(r.weight * decay_weight(r.publish_date, ref_date, lam), 4)
    logger.info("时间衰减完成：λ=%.3f，参考日期 %s", lam, ref_date.isoformat())
    return records