"""计提参数服务：时点化取值（解析部分）。

ParamSnapshot 是 M3 核算与计算预览共用的输入契约：按业务日期（回款到账日）
冻结当时口径，禁读「当前值」计算历史数据（算法红线）。
变更提交/历史/对比/预览/导出在后续任务追加。
"""

from collections.abc import Iterable
from dataclasses import dataclass
from datetime import date
from fractions import Fraction

from sqlalchemy.orm import Session

from app.core.exceptions import BadRequestError
from app.repositories.param_repository import resolve_values
from app.services.param_registry import get_spec, parse_fraction


@dataclass(frozen=True, slots=True)
class ParamSnapshot:
    """某业务日期下的参数快照（冻结不可变，核算期间保持一致）。

    覆盖链：角色维度 > 产品类别维度 > 默认行（''）；均无匹配时回退注册表默认值。
    """

    biz_date: date
    _values: dict[str, dict[str, str]]

    @classmethod
    def from_rows(cls, biz_date: date, rows: Iterable[tuple[str, str, str]]) -> "ParamSnapshot":
        """由 (param_code, dimension_value, value_text) 行构造。

        rows 须按仓储输出顺序（同一 (code, dim) 的最新生效值在前）——以先出现者为准。
        """
        values: dict[str, dict[str, str]] = {}
        for code, dimension, value_text in rows:
            values.setdefault(code, {}).setdefault(dimension, value_text)
        return cls(biz_date=biz_date, _values=values)

    def get(
        self, code: str, *, role_code: str | None = None, product_category: str | None = None
    ) -> str:
        """取参数原始值（覆盖链解析）。无值且无注册表默认值时抛 400。"""
        candidates = self._values.get(code)
        if candidates:
            for dimension in (role_code, product_category, ""):
                if dimension is not None and dimension in candidates:
                    return candidates[dimension]
        spec = get_spec(code)  # 未注册编码 → ValueError（代码缺陷）
        if spec.default_value is None:
            raise BadRequestError(f"参数 {code} 无生效值且无默认值，请先在系统设置中维护")
        return spec.default_value

    def fraction(
        self, code: str, *, role_code: str | None = None, product_category: str | None = None
    ) -> Fraction:
        """取参数值并精确解析为 Fraction（"4/360" → 1/90，不经 float）。"""
        return parse_fraction(
            self.get(code, role_code=role_code, product_category=product_category)
        )

    def integer(
        self, code: str, *, role_code: str | None = None, product_category: str | None = None
    ) -> int:
        """取参数值为整数。配置成非整数属数据缺陷（写入经校验，不应发生）。"""
        value = self.fraction(code, role_code=role_code, product_category=product_category)
        if value.denominator != 1:
            raise ValueError(f"参数 {code} 配置为非整数：{value}")
        return int(value)

    def boolean(
        self, code: str, *, role_code: str | None = None, product_category: str | None = None
    ) -> bool:
        """取布尔参数（0/1）。"""
        return self.get(code, role_code=role_code, product_category=product_category) == "1"

    def text(
        self, code: str, *, role_code: str | None = None, product_category: str | None = None
    ) -> str:
        """取参数原文（枚举码/文本）。"""
        return self.get(code, role_code=role_code, product_category=product_category)


def resolve_snapshot(session: Session, biz_date: date) -> ParamSnapshot:
    """按业务日期解析全量参数快照（M3 核算与计算预览共用入口）。"""
    return ParamSnapshot.from_rows(biz_date, resolve_values(session, biz_date))