"""
Tax simulation service for Korean retirement pension (퇴직연금) tax benefits.
"""

IRP_ANNUAL_LIMIT = 9_000_000  # DC+IRP 합산 연간 한도
INCOME_THRESHOLD = 55_000_000  # 총급여 기준
LOW_INCOME_RATE = 16.5  # 5,500만원 이하 공제율
HIGH_INCOME_RATE = 13.2  # 5,500만원 초과 공제율
LUMP_SUM_TAX_RATE = 16.5  # 기타소득세 (일시금)


def _get_pension_tax_rate(age: int) -> float:
    if age >= 80:
        return 3.3
    elif age >= 70:
        return 4.4
    else:
        return 5.5


def calculate_tax_deduction(
    annual_income: int,
    contribution: int,
    account_type: str,
) -> dict:
    deduction_rate = LOW_INCOME_RATE if annual_income <= INCOME_THRESHOLD else HIGH_INCOME_RATE
    deductible = min(contribution, IRP_ANNUAL_LIMIT)
    tax_deduction = deductible * (deduction_rate / 100)

    return {
        "annual_income": annual_income,
        "contribution": contribution,
        "account_type": account_type,
        "deduction_rate": deduction_rate,
        "irp_limit": IRP_ANNUAL_LIMIT,
        "deductible_contribution": deductible,
        "tax_deduction": tax_deduction,
    }


def calculate_pension_tax(
    withdrawal_amount: int,
    withdrawal_type: str,
    age: int,
) -> dict:
    pension_tax_rate = _get_pension_tax_rate(age)
    pension_tax = withdrawal_amount * (pension_tax_rate / 100)
    lump_sum_tax = withdrawal_amount * (LUMP_SUM_TAX_RATE / 100)
    tax_saving = lump_sum_tax - pension_tax

    return {
        "withdrawal_amount": withdrawal_amount,
        "withdrawal_type": withdrawal_type,
        "age": age,
        "pension_tax_rate": pension_tax_rate,
        "pension_tax": pension_tax,
        "lump_sum_tax_rate": LUMP_SUM_TAX_RATE,
        "lump_sum_tax": lump_sum_tax,
        "tax_saving": tax_saving,
    }


def simulate_accumulation(
    monthly_contribution: int,
    years: int,
    annual_return: float,
    tax_deduction_rate: float,
) -> dict:
    annual_contribution = monthly_contribution * 12
    monthly_return = (1 + annual_return / 100) ** (1 / 12) - 1

    yearly_data = []
    current_value = 0.0
    cumulative_contribution = 0
    cumulative_tax_deduction = 0.0

    for year in range(1, years + 1):
        for _ in range(12):
            current_value = current_value * (1 + monthly_return) + monthly_contribution
        cumulative_contribution += annual_contribution

        deductible = min(annual_contribution, IRP_ANNUAL_LIMIT)
        yearly_tax_deduction = deductible * (tax_deduction_rate / 100)
        cumulative_tax_deduction += yearly_tax_deduction

        yearly_data.append({
            "year": year,
            "contribution": annual_contribution,
            "cumulative_contribution": cumulative_contribution,
            "investment_value": round(current_value, 0),
            "tax_deduction": yearly_tax_deduction,
            "cumulative_tax_deduction": cumulative_tax_deduction,
        })

    total_contribution = annual_contribution * years
    total_return = round(current_value - total_contribution, 0)

    return {
        "monthly_contribution": monthly_contribution,
        "years": years,
        "annual_return": annual_return,
        "tax_deduction_rate": tax_deduction_rate,
        "total_contribution": total_contribution,
        "final_value": round(current_value, 0),
        "total_return": total_return,
        "total_tax_deduction": cumulative_tax_deduction,
        "yearly_data": yearly_data,
    }