"""组合偏离度与调仓建议计算。"""
from __future__ import annotations

from collections import defaultdict
from decimal import Decimal, ROUND_HALF_UP
from typing import Iterable

from common.common_const import (
    CUSTOMER_REL_STATUS_SIGNED,
    ERR_CODE_NOT_SIGNED_REBALANCE,
)
from common.suitability import check_suitability
from utils.exceptions import ApiError


_MONEY = Decimal("0.01")
_PERCENT = Decimal("100")


def _money(value: Decimal) -> Decimal:
    return value.quantize(_MONEY, rounding=ROUND_HALF_UP)


def build_rebalance_plan(
    *,
    relation_status: str,
    customer_risk: str,
    holdings: Iterable[dict],
    target_allocation: dict[str, int | float | Decimal],
    threshold: Decimal,
    candidates: Iterable[dict],
) -> dict | None:
    if relation_status != CUSTOMER_REL_STATUS_SIGNED:
        raise ApiError(ERR_CODE_NOT_SIGNED_REBALANCE, "客户尚未签约，禁止生成调仓草稿")

    values: dict[str, Decimal] = defaultdict(Decimal)
    holdings_by_class: dict[str, list[dict]] = defaultdict(list)
    for holding in holdings:
        asset_class = str(holding.get("asset_class", ""))
        value = Decimal(str(holding.get("market_value", 0) or 0))
        values[asset_class] += value
        holdings_by_class[asset_class].append(holding)

    total = sum(values.values(), Decimal("0"))
    if total <= 0:
        return None

    target = {
        asset_class: Decimal(str(weight)) for asset_class, weight in target_allocation.items()
    }
    deviation: dict[str, Decimal] = {}
    for asset_class in target:
        actual = values.get(asset_class, Decimal("0")) / total * _PERCENT
        deviation[asset_class] = (actual - target[asset_class]).quantize(
            Decimal("0.01"), rounding=ROUND_HALF_UP
        )

    if not any(abs(value) > threshold for value in deviation.values()):
        return None

    sell: list[dict] = []
    buy: list[dict] = []
    for asset_class, drift in deviation.items():
        if drift > threshold:
            target_value = total * target[asset_class] / _PERCENT
            excess = _money(values.get(asset_class, Decimal("0")) - target_value)
            remaining = excess
            for holding in holdings_by_class.get(asset_class, []):
                amount = min(
                    remaining,
                    _money(Decimal(str(holding.get("market_value", 0) or 0))),
                )
                if amount > 0:
                    sell.append(
                        {
                            "product_code": holding.get("product_code"),
                            "asset_class": asset_class,
                            "amount": amount,
                        }
                    )
                    remaining -= amount
                if remaining <= 0:
                    break
        elif drift < -threshold:
            target_value = total * target[asset_class] / _PERCENT
            amount = _money(target_value - values.get(asset_class, Decimal("0")))
            for candidate in candidates:
                if candidate.get("asset_class") != asset_class:
                    continue
                if not check_suitability(
                    customer_risk, candidate.get("risk_level", "")
                ).ok:
                    continue
                buy.append(
                    {
                        "product_code": candidate.get("product_code"),
                        "asset_class": asset_class,
                        "amount": amount,
                    }
                )
                break

    return {
        "deviation": deviation,
        "sell": sell,
        "buy": buy,
    }