"""IRR 精算计算模块 — Modified-Actuarial NPV IRR（二分法）。"""

# HK IA 监管上限
HK_IA_CAP_HKD = 0.06    # HKD 6.0%
HK_IA_CAP_OTHER = 0.065  # 非 HKD 6.5%


def ia_irr_cap(currency: str = "HKD") -> float:
    """HK IA 监管上限。"""
    return HK_IA_CAP_HKD if currency.upper() == "HKD" else HK_IA_CAP_OTHER


def compute_irr_ma(
    annual_prem: float,
    pay_yrs: int,
    sv: float,
    yr: int,
    cap: float = HK_IA_CAP_HKD,
) -> float | None:
    """Modified-Actuarial NPV IRR（二分法 200 次迭代）。

    Args:
        annual_prem: 年缴保费
        pay_yrs: 缴费年期
        sv: 第 yr 年的退保价值
        yr: 保单年度
        cap: IRR 上限（HK IA 监管）

    Returns:
        IRR 值（0~cap 之间），无法计算返回 None
    """
    if yr <= 0 or annual_prem <= 0 or sv <= 0:
        return None

    def npv(r):
        """计算净现值。"""
        if r <= -1:
            return float("inf")
        total = 0.0
        for t in range(1, min(yr, pay_yrs) + 1):
            total += annual_prem / ((1 + r) ** t)
        # 退保价值折现到第 yr 年
        total -= sv / ((1 + r) ** yr)
        return total

    # 二分法求解
    low, high = 0.0, cap
    for _ in range(200):
        mid = (low + high) / 2
        if npv(mid) > 0:
            low = mid
        else:
            high = mid
    return round((low + high) / 2, 6)


def compute_irr_ma_withdraw(
    annual_prem: float,
    pay_yrs: int,
    start_yr: int,
    annual_wd: float,
    sv: float,
    yr: int,
    cap: float = HK_IA_CAP_HKD,
) -> float | None:
    """含退保场景的 Modified-Actuarial NPV IRR。

    Args:
        annual_prem: 年缴保费
        pay_yrs: 缴费年期
        start_yr: 开始退保年度
        annual_wd: 每年退保金额
        sv: 第 yr 年的退保价值
        yr: 保单年度
        cap: IRR 上限

    Returns:
        IRR 值，无法计算返回 None
    """
    if yr <= 0 or annual_prem <= 0:
        return None

    def npv(r):
        if r <= -1:
            return float("inf")
        total = 0.0
        for t in range(1, min(yr, pay_yrs) + 1):
            total += annual_prem / ((1 + r) ** t)
        # 退保收入折现
        for t in range(start_yr, yr + 1):
            total -= annual_wd / ((1 + r) ** t)
        # 最终退保价值折现
        total -= sv / ((1 + r) ** yr)
        return total

    low, high = -0.01, cap
    for _ in range(200):
        mid = (low + high) / 2
        if npv(mid) > 0:
            low = mid
        else:
            high = mid
    return round((low + high) / 2, 6)