hmrc-rates 0.3.0

use rust_decimal::Decimal;

use crate::types::{Currency, Period};

/// A resolved HMRC rate: currency units per £1, with exact `Decimal` arithmetic.
///
/// The crate never rounds.
/// Callers apply whatever rounding their tax context requires.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct Rate {
    units_per_gbp: Decimal,
    currency: Currency,
    period: Period,
}

impl Rate {
    pub(crate) fn new(units_per_gbp: Decimal, currency: Currency, period: Period) -> Rate {
        Rate {
            units_per_gbp,
            currency,
            period,
        }
    }

    /// The canonical HMRC figure: how many currency units £1 buys.
    pub fn units_per_gbp(&self) -> Decimal {
        self.units_per_gbp
    }

    /// Converts an amount in this rate's currency to GBP (`amount / units_per_gbp`).
    ///
    /// Exact division, round the result yourself.
    ///
    /// # Examples
    ///
    /// ```
    /// use hmrc_rates::{YearMonth, Rates};
    /// use rust_decimal::Decimal;
    ///
    /// let rates = Rates::new();
    /// let usd = rates.monthly_rate("USD", YearMonth::new(2025, 8).unwrap())?;
    /// let gbp = usd.to_gbp(Decimal::from(2500));
    /// println!("£{}", gbp.round_dp(2));
    /// # Ok::<(), hmrc_rates::LookupError>(())
    /// ```
    pub fn to_gbp(&self, amount: Decimal) -> Decimal {
        amount / self.units_per_gbp
    }

    /// Converts a GBP amount to this rate's currency (`gbp * units_per_gbp`).
    pub fn from_gbp(&self, gbp: Decimal) -> Decimal {
        gbp * self.units_per_gbp
    }

    /// The currency this rate quotes against GBP.
    pub fn currency(&self) -> Currency {
        self.currency
    }

    /// The period the rate was published for.
    /// Reveals the substituted month after
    /// [`Rates::monthly_rate_or_earlier`](crate::Rates::monthly_rate_or_earlier).
    pub fn period(&self) -> Period {
        self.period
    }
}