from __future__ import annotations

from dataclasses import dataclass


@dataclass(frozen=True)
class LombardPortfolio:
    """Lombard loan portfolio backed by physical gold.

    Attributes:
        gold_ounces: Quantity of pledged gold in troy ounces.
        gold_price_per_ounce: Current gold spot price per ounce.
        loan_amount: Outstanding Lombard loan balance.
        initial_ltv: Origination or current reference loan-to-value ratio.
        margin_call_ltv: LTV threshold at which a margin call is triggered.
    """

    gold_ounces: float
    gold_price_per_ounce: float
    loan_amount: float
    initial_ltv: float
    margin_call_ltv: float

    def __post_init__(self) -> None:
        if self.gold_ounces <= 0:
            raise ValueError("gold_ounces must be positive")
        if self.gold_price_per_ounce <= 0:
            raise ValueError("gold_price_per_ounce must be positive")
        if self.loan_amount < 0:
            raise ValueError("loan_amount must be non-negative")
        if not 0 < self.initial_ltv < 1:
            raise ValueError("initial_ltv must be between 0 and 1")
        if not 0 < self.margin_call_ltv < 1:
            raise ValueError("margin_call_ltv must be between 0 and 1")
        if self.initial_ltv > self.margin_call_ltv:
            raise ValueError("initial_ltv cannot exceed margin_call_ltv")
        if self.loan_amount > self.gold_value:
            raise ValueError("loan_amount cannot exceed current gold value")

    @property
    def gold_value(self) -> float:
        """Current market value of pledged gold."""
        return self.gold_ounces * self.gold_price_per_ounce

    @property
    def current_ltv(self) -> float:
        """Current loan-to-value ratio."""
        return self.loan_amount / self.gold_value

    @property
    def net_equity(self) -> float:
        """Equity remaining after subtracting the loan from gold value."""
        return self.gold_value - self.loan_amount

    def gold_value_at_price(self, gold_price_per_ounce: float) -> float:
        """Gold value under an alternative spot-price scenario."""
        if gold_price_per_ounce <= 0:
            raise ValueError("gold_price_per_ounce must be positive")
        return self.gold_ounces * gold_price_per_ounce

    def ltv_at_price(self, gold_price_per_ounce: float) -> float:
        """Portfolio LTV under an alternative gold-price scenario."""
        return self.loan_amount / self.gold_value_at_price(gold_price_per_ounce)

    def net_equity_at_price(self, gold_price_per_ounce: float) -> float:
        """Net equity under an alternative gold-price scenario."""
        return self.gold_value_at_price(gold_price_per_ounce) - self.loan_amount

    def margin_call_price(self) -> float:
        """Gold price per ounce at which the portfolio breaches the margin LTV."""
        return self.loan_amount / (self.margin_call_ltv * self.gold_ounces)