libitofin 0.6.1

//! Term-structure base machinery.
//!
//! Port of `ql/termstructure.{hpp,cpp}`: the [`TermStructure`] trait is the
//! curve contract (C++'s virtual interface) and [`TermStructureBase`] is the
//! shared holder concrete curves embed (C++'s data members and default
//! behaviour). A term structure keeps track of its reference date in one of
//! three ways: a fixed date, a date moving off the evaluation date (advanced
//! by a number of settlement days on a calendar), or a date managed by the
//! concrete curve itself (which then overrides
//! [`reference_date`](TermStructure::reference_date)).
//!
//! ## Divergences from QuantLib
//!
//! - QuantLib's moving mode reads the global `Settings` singleton; per D5 the
//!   moving constructor takes the shared [`Settings`] handle explicitly and
//!   registers with its evaluation-date observable. The date mutates through
//!   `&self`, so an observer may read the reference date back while the
//!   evaluation-date notification that invalidated it is still running.
//! - A base asked for a reference date it does not manage returns an `Err`
//!   where C++ silently returns the null date.
//! - C++'s `Extrapolator` base class is folded into the holder as a flag; it
//!   can be extracted once the interpolation layer needs it.
//! - The empty `Calendar`/`DayCounter` states are `Option`s here, per the
//!   [`DayCounter`] port convention.
//! - No today's-date fallback: C++ resolves an unset evaluation date to
//!   `Date::todaysDate()`; this port has no system-clock date, so a moving
//!   structure returns an `Err` until the evaluation date is set explicitly.
//! - The moving recompute reads the constructor-stored calendar and
//!   settlement days; a curve overriding
//!   [`calendar`](TermStructure::calendar) or
//!   [`settlement_days`](TermStructure::settlement_days) (C++ dispatches
//!   through the virtuals) must override
//!   [`reference_date`](TermStructure::reference_date) as well.

pub mod bootstraphelper;
pub mod bootstraptraits;
pub mod interpolatedcurve;
pub mod iterativebootstrap;
pub mod volatility;
pub mod yields;
pub mod yieldtermstructure;

pub use bootstraphelper::{
    BootstrapHelperBase, RateHelper, RelativeDateRateHelper, compare_by_pillar_date,
    sort_by_pillar_date,
};

use std::cell::Cell;

use crate::errors::QlResult;
use crate::math::comparison::close_enough;
use crate::patterns::observable::{AsObservable, Observable, Observer, ResetThenNotify};
use crate::settings::Settings;
use crate::shared::{Shared, SharedMut, shared};
use crate::time::businessdayconvention::BusinessDayConvention;
use crate::time::calendar::Calendar;
use crate::time::date::Date;
use crate::time::daycounter::DayCounter;
use crate::time::timeunit::TimeUnit;
use crate::types::{Integer, Natural, Time};
use crate::{fail, require};

/// The lazily recomputed reference date shared between the holder and its
/// observer half (C++'s `mutable referenceDate_`/`updated_`/`moving_`;
/// `None` means stale for a moving structure and unmanaged otherwise).
struct ReferenceState {
    date: Cell<Option<Date>>,
    moving: bool,
}

/// Shared base holder for term structures.
///
/// Concrete curves embed one, delegate the [`TermStructure`] trait's
/// `base()` accessor to it, and expose its [`observable`](Self::observable)
/// through [`AsObservable`].
pub struct TermStructureBase {
    calendar: Option<Calendar>,
    settlement_days: Option<Natural>,
    day_counter: Option<DayCounter>,
    settings: Option<Shared<Settings<Date>>>,
    extrapolation: Cell<bool>,
    reference: Shared<ReferenceState>,
    observable: Shared<Observable>,
    updater: SharedMut<ResetThenNotify>,
}

impl TermStructureBase {
    fn assemble(
        calendar: Option<Calendar>,
        settlement_days: Option<Natural>,
        day_counter: Option<DayCounter>,
        settings: Option<Shared<Settings<Date>>>,
        moving: bool,
        reference_date: Option<Date>,
    ) -> TermStructureBase {
        let reference = shared(ReferenceState {
            date: Cell::new(reference_date),
            moving,
        });
        let observable = shared(Observable::new());
        let updater = ResetThenNotify::broadcasting(Shared::clone(&observable), {
            let reference = Shared::clone(&reference);
            move || {
                if reference.moving {
                    reference.date.set(None);
                }
            }
        });
        TermStructureBase {
            calendar,
            settlement_days,
            day_counter,
            settings,
            extrapolation: Cell::new(false),
            reference,
            observable,
            updater,
        }
    }

    /// Base for a curve that manages its own reference date by overriding
    /// [`TermStructure::reference_date`] (C++'s default constructor).
    pub fn new(day_counter: Option<DayCounter>) -> TermStructureBase {
        Self::assemble(None, None, day_counter, None, false, None)
    }

    /// Base with a fixed reference date.
    pub fn with_reference_date(
        reference_date: Date,
        calendar: Option<Calendar>,
        day_counter: Option<DayCounter>,
    ) -> TermStructureBase {
        Self::assemble(
            calendar,
            None,
            day_counter,
            None,
            false,
            Some(reference_date),
        )
    }

    /// Base whose reference date moves off the evaluation date, advanced by
    /// `settlement_days` business days on `calendar`.
    ///
    /// Registers with the settings' evaluation-date observable: a date change
    /// invalidates the cached reference date and notifies the structure's
    /// observers.
    pub fn moving(
        settlement_days: Natural,
        calendar: Calendar,
        day_counter: Option<DayCounter>,
        settings: Shared<Settings<Date>>,
    ) -> TermStructureBase {
        let base = Self::assemble(
            Some(calendar),
            Some(settlement_days),
            day_counter,
            Some(Shared::clone(&settings)),
            true,
            None,
        );
        settings.register_eval_date_observer(&(base.updater.clone() as SharedMut<dyn Observer>));
        base
    }

    /// The date at which discount = 1.0 and/or variance = 0.0, recomputing it
    /// off the evaluation date first when the structure is moving.
    pub fn reference_date(&self) -> QlResult<Date> {
        if self.reference.moving && self.reference.date.get().is_none() {
            let settings = self
                .settings
                .as_ref()
                .expect("a moving term structure holds settings");
            let Some(today) = settings.evaluation_date() else {
                fail!("no evaluation date set: a moving term structure needs one");
            };
            require!(
                today != Date::null(),
                "null evaluation date set for a moving term structure"
            );
            let days = self
                .settlement_days
                .expect("a moving term structure holds settlement days");
            let Ok(n) = Integer::try_from(days) else {
                fail!("settlement days ({days}) overflow Integer");
            };
            let horizon = (i64::from(days) + 1) * 10;
            require!(
                i64::from(today.serial_number()) + horizon
                    <= i64::from(Date::max_date().serial_number()),
                "evaluation date ({today}) is too close to the maximum date to advance {days} settlement days"
            );
            let calendar = self
                .calendar
                .as_ref()
                .expect("a moving term structure holds a calendar");
            let advanced = calendar.advance(
                today,
                n,
                TimeUnit::Days,
                BusinessDayConvention::Following,
                false,
            );
            self.reference.date.set(Some(advanced));
        }
        match self.reference.date.get() {
            Some(date) if date != Date::null() => Ok(date),
            _ => fail!("no reference date provided: construct with one or override reference_date"),
        }
    }

    /// The day counter used for date/time conversion, when provided.
    pub fn day_counter(&self) -> Option<DayCounter> {
        self.day_counter.clone()
    }

    /// The calendar used for reference-date calculation, when provided.
    pub fn calendar(&self) -> Option<Calendar> {
        self.calendar.clone()
    }

    /// The settlement days used for reference-date calculation.
    pub fn settlement_days(&self) -> QlResult<Natural> {
        match self.settlement_days {
            Some(days) => Ok(days),
            None => fail!("settlement days not provided for this instance"),
        }
    }

    /// The observable notifying the structure's observers.
    pub fn observable(&self) -> &Observable {
        &self.observable
    }

    /// The structure's observer half, for registering with further
    /// observables (a quote handle, another curve); notifications received
    /// through it behave like C++'s `TermStructure::update()`.
    pub fn updater(&self) -> SharedMut<dyn Observer> {
        self.updater.clone()
    }

    /// Whether the curve answers dates/times beyond its maximum.
    pub fn allows_extrapolation(&self) -> bool {
        self.extrapolation.get()
    }

    /// Allows extrapolation past the maximum date/time.
    pub fn enable_extrapolation(&self) {
        self.extrapolation.set(true);
    }

    /// Forbids extrapolation past the maximum date/time.
    pub fn disable_extrapolation(&self) {
        self.extrapolation.set(false);
    }
}

/// Basic term-structure functionality.
///
/// Mirrors QuantLib's `TermStructure` interface; the provided methods
/// delegate to the embedded [`TermStructureBase`] exactly as the C++ base
/// class implements them, and a concrete curve overrides the ones it manages
/// itself (typically [`reference_date`](Self::reference_date) when built via
/// [`TermStructureBase::new`]).
pub trait TermStructure: AsObservable {
    /// The embedded shared holder.
    fn base(&self) -> &TermStructureBase;

    /// The latest date for which the curve can return values.
    fn max_date(&self) -> Date;

    /// The day counter used for date/time conversion, when provided.
    fn day_counter(&self) -> Option<DayCounter> {
        self.base().day_counter()
    }

    /// The day counter, or an error for structures built without one.
    fn require_day_counter(&self) -> QlResult<DayCounter> {
        let Some(day_counter) = self.day_counter() else {
            fail!("no day counter provided for this term structure");
        };
        Ok(day_counter)
    }

    /// The calendar used for reference-date calculation, when provided.
    fn calendar(&self) -> Option<Calendar> {
        self.base().calendar()
    }

    /// The settlement days used for reference-date calculation.
    fn settlement_days(&self) -> QlResult<Natural> {
        self.base().settlement_days()
    }

    /// The date at which discount = 1.0 and/or variance = 0.0.
    fn reference_date(&self) -> QlResult<Date> {
        self.base().reference_date()
    }

    /// The period from the reference date to `date` as a year fraction.
    fn time_from_reference(&self, date: Date) -> QlResult<Time> {
        let day_counter = self.require_day_counter()?;
        Ok(day_counter.year_fraction(self.reference_date()?, date))
    }

    /// The latest time for which the curve can return values.
    fn max_time(&self) -> QlResult<Time> {
        self.time_from_reference(self.max_date())
    }

    /// Whether the curve answers dates/times beyond its maximum.
    fn allows_extrapolation(&self) -> bool {
        self.base().allows_extrapolation()
    }

    /// Allows extrapolation past the maximum date/time.
    fn enable_extrapolation(&self) {
        self.base().enable_extrapolation()
    }

    /// Forbids extrapolation past the maximum date/time.
    fn disable_extrapolation(&self) {
        self.base().disable_extrapolation()
    }

    /// Date-range check: `date` must not precede the reference date nor,
    /// unless extrapolation applies, exceed the maximum date.
    fn check_range_date(&self, date: Date, extrapolate: bool) -> QlResult<()> {
        let reference = self.reference_date()?;
        require!(
            date >= reference,
            "date ({date}) before reference date ({reference})"
        );
        require!(
            extrapolate || self.allows_extrapolation() || date <= self.max_date(),
            "date ({date}) is past max curve date ({max})",
            max = self.max_date()
        );
        Ok(())
    }

    /// Time-range check: `t` must be finite, non-negative and, unless
    /// extrapolation applies, within the maximum time.
    ///
    /// The `t >= 0` requirement is QuantLib's `checkRange`
    /// (`termstructure.cpp:66`). Divergence: the finiteness clause. `+inf`
    /// passes `t >= 0` in C++, and an extrapolating curve never compares it
    /// against `maxTime()`, so it reaches the interpolator unchecked.
    fn check_range_time(&self, t: Time, extrapolate: bool) -> QlResult<()> {
        if !t.is_finite() || t < 0.0 {
            fail!("negative time ({t}) given");
        }
        if extrapolate || self.allows_extrapolation() {
            return Ok(());
        }
        let max_time = self.max_time()?;
        require!(
            t <= max_time || close_enough(t, max_time),
            "time ({t}) is past max curve time ({max_time})"
        );
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::test_support::{Flag, as_observer};
    use crate::time::calendars::target::Target;
    use crate::time::date::Month;
    use crate::time::daycounters::actual360::Actual360;

    struct TestCurve {
        base: TermStructureBase,
        max: Date,
    }

    impl TestCurve {
        fn fixed(reference_date: Date) -> TestCurve {
            TestCurve {
                base: TermStructureBase::with_reference_date(
                    reference_date,
                    None,
                    Some(Actual360::new()),
                ),
                max: reference_date + 360,
            }
        }
    }

    impl AsObservable for TestCurve {
        fn observable(&self) -> &Observable {
            self.base.observable()
        }
    }

    impl TermStructure for TestCurve {
        fn base(&self) -> &TermStructureBase {
            &self.base
        }

        fn max_date(&self) -> Date {
            self.max
        }
    }

    #[test]
    fn fixed_reference_date_is_returned_verbatim() {
        let reference = Date::new(15, Month::June, 2026);
        let curve = TestCurve::fixed(reference);
        assert_eq!(curve.reference_date().unwrap(), reference);
        assert!(curve.settlement_days().is_err());
        assert!(curve.calendar().is_none());
    }

    #[test]
    fn time_from_reference_uses_the_day_counter() {
        let reference = Date::new(15, Month::June, 2026);
        let curve = TestCurve::fixed(reference);
        let half_year = curve.time_from_reference(reference + 180).unwrap();
        assert_eq!(half_year, 0.5);
        assert_eq!(curve.max_time().unwrap(), 1.0);
    }

    #[test]
    fn moving_reference_date_advances_off_the_evaluation_date() {
        let settings = shared(Settings::new());
        settings.set_evaluation_date(Date::new(15, Month::January, 2026));
        let curve = TestCurve {
            base: TermStructureBase::moving(
                2,
                Target::new(),
                Some(Actual360::new()),
                settings.clone(),
            ),
            max: Date::new(15, Month::January, 2027),
        };
        assert_eq!(
            curve.reference_date().unwrap(),
            Date::new(19, Month::January, 2026)
        );
        assert_eq!(curve.settlement_days().unwrap(), 2);
    }

    #[test]
    fn evaluation_date_change_recomputes_reference_and_notifies() {
        let settings = shared(Settings::new());
        settings.set_evaluation_date(Date::new(15, Month::January, 2026));
        let curve = TestCurve {
            base: TermStructureBase::moving(
                0,
                Target::new(),
                Some(Actual360::new()),
                settings.clone(),
            ),
            max: Date::new(15, Month::January, 2027),
        };
        assert_eq!(
            curve.reference_date().unwrap(),
            Date::new(15, Month::January, 2026)
        );

        let flag = Flag::new();
        curve.observable().register_observer(&as_observer(&flag));
        settings.set_evaluation_date(Date::new(16, Month::January, 2026));

        assert!(Flag::is_up(&flag));
        assert_eq!(
            curve.reference_date().unwrap(),
            Date::new(16, Month::January, 2026)
        );
    }

    #[test]
    fn moving_without_evaluation_date_is_an_error() {
        let settings = shared(Settings::new());
        let base = TermStructureBase::moving(2, Target::new(), Some(Actual360::new()), settings);
        let err = base.reference_date().unwrap_err();
        assert!(err.message().contains("no evaluation date set"));
    }

    #[test]
    fn null_or_near_max_evaluation_dates_are_errors_not_panics() {
        let settings = shared(Settings::new());
        let base =
            TermStructureBase::moving(2, Target::new(), Some(Actual360::new()), settings.clone());

        settings.set_evaluation_date(Date::null());
        let err = base.reference_date().unwrap_err();
        assert!(err.message().contains("null evaluation date"));

        settings.set_evaluation_date(Date::max_date());
        let err = base.reference_date().unwrap_err();
        assert!(err.message().contains("too close to the maximum date"));
    }

    #[test]
    fn extrapolation_short_circuits_before_max_time_is_computed() {
        struct NoDayCounterCurve {
            base: TermStructureBase,
        }
        impl AsObservable for NoDayCounterCurve {
            fn observable(&self) -> &Observable {
                self.base.observable()
            }
        }
        impl TermStructure for NoDayCounterCurve {
            fn base(&self) -> &TermStructureBase {
                &self.base
            }
            fn max_date(&self) -> Date {
                Date::max_date()
            }
        }

        let curve = NoDayCounterCurve {
            base: TermStructureBase::new(None),
        };
        assert!(curve.check_range_time(0.5, true).is_ok());
        curve.enable_extrapolation();
        assert!(curve.check_range_time(0.5, false).is_ok());
        curve.disable_extrapolation();
        assert!(curve.check_range_time(0.5, false).is_err());
    }

    #[test]
    fn range_check_rejects_non_finite_time_even_with_extrapolation() {
        let curve = TestCurve::fixed(Date::new(15, Month::June, 2026));
        curve.enable_extrapolation();

        assert!(curve.check_range_time(Time::INFINITY, false).is_err());
        assert!(curve.check_range_time(Time::NEG_INFINITY, true).is_err());
        assert!(curve.check_range_time(Time::NAN, true).is_err());
    }

    #[test]
    fn detached_base_has_no_reference_date() {
        let base = TermStructureBase::new(Some(Actual360::new()));
        assert!(base.reference_date().is_err());
        assert!(base.settlement_days().is_err());
    }

    #[test]
    fn updater_forwards_notifications_without_touching_a_fixed_reference() {
        let reference = Date::new(15, Month::June, 2026);
        let curve = TestCurve::fixed(reference);
        let flag = Flag::new();
        curve.observable().register_observer(&as_observer(&flag));

        let source = Observable::new();
        source.register_observer(&curve.base().updater());
        source.notify_observers();

        assert!(Flag::is_up(&flag));
        assert_eq!(curve.reference_date().unwrap(), reference);
    }

    #[test]
    fn check_range_date_enforces_reference_and_max() {
        let reference = Date::new(15, Month::June, 2026);
        let curve = TestCurve::fixed(reference);

        assert!(curve.check_range_date(reference, false).is_ok());
        assert!(curve.check_range_date(curve.max_date(), false).is_ok());

        let before = curve.check_range_date(reference - 1, false).unwrap_err();
        assert!(before.message().contains("before reference date"));

        let past = curve
            .check_range_date(curve.max_date() + 1, false)
            .unwrap_err();
        assert!(past.message().contains("past max curve date"));

        assert!(curve.check_range_date(curve.max_date() + 1, true).is_ok());
        curve.enable_extrapolation();
        assert!(curve.check_range_date(curve.max_date() + 1, false).is_ok());
        curve.disable_extrapolation();
        assert!(curve.check_range_date(curve.max_date() + 1, false).is_err());
    }

    #[test]
    fn check_range_time_enforces_sign_and_max() {
        let curve = TestCurve::fixed(Date::new(15, Month::June, 2026));

        assert!(curve.check_range_time(0.0, false).is_ok());
        assert!(curve.check_range_time(1.0, false).is_ok());

        let negative = curve.check_range_time(-0.1, false).unwrap_err();
        assert!(negative.message().contains("negative time"));
        assert!(curve.check_range_time(Time::NAN, false).is_err());

        let past = curve.check_range_time(1.5, false).unwrap_err();
        assert!(past.message().contains("past max curve time"));

        assert!(curve.check_range_time(1.5, true).is_ok());
        curve.enable_extrapolation();
        assert!(curve.check_range_time(1.5, false).is_ok());
    }
}