from __future__ import annotations

from dataclasses import dataclass
from datetime import date
from decimal import ROUND_HALF_UP, Decimal

MONEY = Decimal("0.01")


@dataclass(frozen=True)
class LoanPayment:
    number: int
    payment_date: date | None
    payment: Decimal
    principal: Decimal
    interest: Decimal
    remaining_principal: Decimal


def quantize_money(value: Decimal) -> Decimal:
    return value.quantize(MONEY, rounding=ROUND_HALF_UP)


def annuity_payment(principal: Decimal, months: int, annual_rate: Decimal) -> Decimal:
    if principal <= 0:
        raise ValueError("principal must be positive")
    if months <= 0:
        raise ValueError("months must be positive")
    if annual_rate < 0:
        raise ValueError("annual_rate must be non-negative")
    if annual_rate == 0:
        return quantize_money(principal / Decimal(months))
    monthly_rate = annual_rate / Decimal("12") / Decimal("100")
    factor = (Decimal("1") + monthly_rate) ** months
    payment = principal * monthly_rate * factor / (factor - Decimal("1"))
    return quantize_money(payment)


def loan_summary(principal: Decimal, months: int, annual_rate: Decimal) -> dict:
    payment = annuity_payment(principal, months, annual_rate)
    total_payment = quantize_money(payment * Decimal(months))
    total_interest = max(total_payment - principal, Decimal("0")).quantize(MONEY)
    return {
        "monthly_payment": payment,
        "total_payment": total_payment,
        "overpayment": total_interest,
        "total_interest": total_interest,
        "principal": principal,
        "months": months,
        "annual_rate": annual_rate,
    }


def generate_annuity_schedule(
    *,
    principal: Decimal,
    months: int,
    annual_rate: Decimal,
    first_payment_date: date | None = None,
) -> list[LoanPayment]:
    payment = annuity_payment(principal, months, annual_rate)
    monthly_rate = annual_rate / Decimal("12") / Decimal("100")
    remaining = principal
    rows: list[LoanPayment] = []
    for number in range(1, months + 1):
        interest = quantize_money(remaining * monthly_rate) if annual_rate else Decimal("0.00")
        principal_part = payment - interest
        if number == months or principal_part > remaining:
            principal_part = remaining
            payment_for_row = principal_part + interest
        else:
            payment_for_row = payment
        remaining = max(remaining - principal_part, Decimal("0"))
        rows.append(
            LoanPayment(
                number=number,
                payment_date=None if first_payment_date is None else add_months(first_payment_date, number - 1),
                payment=quantize_money(payment_for_row),
                principal=quantize_money(principal_part),
                interest=quantize_money(interest),
                remaining_principal=quantize_money(remaining),
            )
        )
    return rows


def add_months(value: date, months: int) -> date:
    import calendar

    month = value.month - 1 + months
    year = value.year + month // 12
    month = month % 12 + 1
    day = min(value.day, calendar.monthrange(year, month)[1])
    return date(year, month, day)