orts 0.1.0

use std::marker::PhantomData;

use arika::epoch::Epoch;
use arika::frame::{Eci, SimpleEci};
use utsuroi::DynamicalSystem;

use super::gravity::GravityField;
use crate::model::Model;
use crate::orbital::OrbitalState;

/// Orbital dynamics system combining a gravity field model with perturbation forces.
///
/// Parameterized by the inertial frame `F` (default `SimpleEci`).
/// All models must produce [`ExternalLoads<F>`](crate::model::ExternalLoads)
/// in the same frame.
pub struct OrbitalSystem<F: Eci = SimpleEci> {
    pub mu: f64,
    pub gravity: Box<dyn GravityField>,
    pub models: Vec<Box<dyn Model<OrbitalState<F>, F>>>,
    /// Initial epoch corresponding to integration time t=0.
    /// Used to compute absolute epoch for time-dependent perturbations (e.g., third-body).
    pub epoch_0: Option<Epoch>,
    /// Equatorial radius of the central body [km]. Used for collision detection.
    pub body_radius: Option<f64>,
    _frame: PhantomData<F>,
}

// Manual Send + Sync: all fields are Send + Sync, PhantomData<F> is fine
// because F is a ZST frame marker.
unsafe impl<F: Eci> Send for OrbitalSystem<F> {}
unsafe impl<F: Eci> Sync for OrbitalSystem<F> {}

impl<F: Eci> OrbitalSystem<F> {
    pub fn new(mu: f64, gravity: Box<dyn GravityField>) -> Self {
        Self {
            mu,
            gravity,
            models: Vec::new(),
            epoch_0: None,
            body_radius: None,
            _frame: PhantomData,
        }
    }

    pub fn with_model(mut self, model: impl Model<OrbitalState<F>, F> + 'static) -> Self {
        self.models.push(Box::new(model));
        self
    }

    pub fn with_epoch(mut self, epoch: Epoch) -> Self {
        self.epoch_0 = Some(epoch);
        self
    }

    pub fn with_body_radius(mut self, radius: f64) -> Self {
        self.body_radius = Some(radius);
        self
    }

    /// Compute per-force acceleration magnitudes [km/s²].
    ///
    /// Returns a vec of (name, magnitude) pairs: `"gravity"` first,
    /// then each model by its [`Model::name()`].
    pub fn acceleration_breakdown(&self, t: f64, state: &OrbitalState<F>) -> Vec<(&str, f64)> {
        let epoch = self.epoch_0.map(|e| e.add_seconds(t));
        let grav = self
            .gravity
            .acceleration(self.mu, state.position())
            .magnitude();
        let mut result = vec![("gravity", grav)];
        for m in &self.models {
            let loads = m.eval(t, state, epoch.as_ref());
            result.push((m.name(), loads.acceleration_inertial.magnitude()));
        }
        result
    }

    /// Names of active models (excluding gravity).
    pub fn model_names(&self) -> Vec<&str> {
        self.models.iter().map(|m| m.name()).collect()
    }
}

impl<F: Eci> DynamicalSystem for OrbitalSystem<F> {
    type State = OrbitalState<F>;
    fn derivatives(&self, t: f64, state: &OrbitalState<F>) -> OrbitalState<F> {
        let epoch = self.epoch_0.map(|e| e.add_seconds(t));
        let mut accel = self.gravity.acceleration(self.mu, state.position());
        for m in &self.models {
            let loads = m.eval(t, state, epoch.as_ref());
            accel += loads.acceleration_inertial.into_inner();
        }
        OrbitalState::from_derivative_in_frame(*state.velocity(), accel)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::orbital::gravity::{PointMass, ZonalHarmonics};
    use crate::orbital::kepler::KeplerianElements;
    use crate::orbital::two_body::TwoBodySystem;
    use arika::earth::{J2 as J2_EARTH, MU as MU_EARTH, R as R_EARTH};
    use nalgebra::vector;
    use std::f64::consts::PI;
    use utsuroi::{Integrator, Rk4};

    #[test]
    fn point_mass_matches_two_body_acceleration() {
        let two_body = TwoBodySystem { mu: MU_EARTH };
        let orbital = OrbitalSystem::new(MU_EARTH, Box::new(PointMass));

        let state = OrbitalState::new(vector![6778.137, 0.0, 0.0], vector![0.0, 7.6693, 0.0]);

        let d1 = two_body.derivatives(0.0, &state);
        let d2 = orbital.derivatives(0.0, &state);

        // Derivatives stored as OrbitalState: .position() = velocity, .velocity() = acceleration
        assert_eq!(d1.position(), d2.position());
        assert!((*d1.velocity() - *d2.velocity()).magnitude() < 1e-15);
    }

    #[test]
    fn point_mass_matches_two_body_propagation() {
        let r = R_EARTH + 400.0;
        let v = (MU_EARTH / r).sqrt();
        let period = 2.0 * PI * (r.powi(3) / MU_EARTH).sqrt();
        let dt = 10.0;

        let initial = OrbitalState::new(vector![r, 0.0, 0.0], vector![0.0, v, 0.0]);

        let two_body = TwoBodySystem { mu: MU_EARTH };
        let final_tb = Rk4.integrate(&two_body, initial.clone(), 0.0, period, dt, |_, _| {});

        let orbital = OrbitalSystem::new(MU_EARTH, Box::new(PointMass));
        let final_os = Rk4.integrate(&orbital, initial, 0.0, period, dt, |_, _| {});

        // Should be bit-for-bit identical
        assert_eq!(final_tb.position(), final_os.position());
        assert_eq!(final_tb.velocity(), final_os.velocity());
    }

    #[test]
    fn orbital_system_with_body_radius() {
        let system: OrbitalSystem =
            OrbitalSystem::new(MU_EARTH, Box::new(PointMass)).with_body_radius(R_EARTH);
        assert_eq!(system.body_radius, Some(R_EARTH));
    }

    #[test]
    fn orbital_system_default_no_body_radius() {
        let system: OrbitalSystem = OrbitalSystem::new(MU_EARTH, Box::new(PointMass));
        assert_eq!(system.body_radius, None);
    }

    fn earth_j2_system() -> OrbitalSystem {
        OrbitalSystem::new(
            MU_EARTH,
            Box::new(ZonalHarmonics {
                r_body: R_EARTH,
                j2: J2_EARTH,
                j3: None,
                j4: None,
            }),
        )
    }

    /// Propagate and return the final RAAN after duration seconds.
    fn propagate_raan(
        system: &OrbitalSystem,
        elements: &KeplerianElements,
        dt: f64,
        duration: f64,
    ) -> f64 {
        let (pos, vel) = elements.to_state_vector(MU_EARTH);
        let initial = OrbitalState::new(pos, vel);

        let final_state = Rk4.integrate(system, initial, 0.0, duration, dt, |_, _| {});

        let final_elements = KeplerianElements::from_state_vector(
            final_state.position(),
            final_state.velocity(),
            MU_EARTH,
        );
        final_elements.raan
    }

    #[test]
    fn j2_iss_raan_precession() {
        let a = R_EARTH + 400.0;
        let i = 51.6_f64.to_radians();
        let n = (MU_EARTH / a.powi(3)).sqrt();
        let expected_rate = -1.5 * n * J2_EARTH * (R_EARTH / a).powi(2) * i.cos();
        let expected_deg_per_day = expected_rate.to_degrees() * 86400.0;

        let system = earth_j2_system();
        let elements = KeplerianElements {
            semi_major_axis: a,
            eccentricity: 0.0001,
            inclination: i,
            raan: 0.0,
            argument_of_periapsis: 0.0,
            true_anomaly: 0.0,
        };

        let duration = 86400.0;
        let dt = 5.0;
        let final_raan = propagate_raan(&system, &elements, dt, duration);

        let raan_change_deg = final_raan.to_degrees();
        let raan_change_deg = if raan_change_deg > 180.0 {
            raan_change_deg - 360.0
        } else {
            raan_change_deg
        };

        assert!(
            (raan_change_deg - expected_deg_per_day).abs() < 0.5,
            "ISS RAAN precession: expected≈{expected_deg_per_day:.2} deg/day, got={raan_change_deg:.2} deg/day"
        );
    }

    #[test]
    fn j2_sso_raan_precession() {
        let a = R_EARTH + 800.0;
        let i = 98.6_f64.to_radians();
        let n = (MU_EARTH / a.powi(3)).sqrt();
        let expected_rate = -1.5 * n * J2_EARTH * (R_EARTH / a).powi(2) * i.cos();
        let expected_deg_per_day = expected_rate.to_degrees() * 86400.0;

        let system = earth_j2_system();
        let elements = KeplerianElements {
            semi_major_axis: a,
            eccentricity: 0.0001,
            inclination: i,
            raan: 0.0,
            argument_of_periapsis: 0.0,
            true_anomaly: 0.0,
        };

        let duration = 86400.0;
        let dt = 5.0;
        let final_raan = propagate_raan(&system, &elements, dt, duration);

        let raan_change_deg = final_raan.to_degrees();
        let raan_change_deg = if raan_change_deg > 180.0 {
            raan_change_deg - 360.0
        } else {
            raan_change_deg
        };

        assert!(
            (raan_change_deg - expected_deg_per_day).abs() < 0.3,
            "SSO RAAN precession: expected≈{expected_deg_per_day:.3} deg/day, got={raan_change_deg:.3} deg/day"
        );
        assert!(
            raan_change_deg > 0.0,
            "SSO RAAN should precess prograde, got={raan_change_deg:.3} deg/day"
        );
    }

    #[test]
    fn j2_dt_convergence() {
        let system = earth_j2_system();
        let a = R_EARTH + 400.0;
        let i = 51.6_f64.to_radians();
        let elements = KeplerianElements {
            semi_major_axis: a,
            eccentricity: 0.0001,
            inclination: i,
            raan: 0.0,
            argument_of_periapsis: 0.0,
            true_anomaly: 0.0,
        };
        let (pos, vel) = elements.to_state_vector(MU_EARTH);
        let initial = OrbitalState::new(pos, vel);

        let duration = 1000.0;
        let dt_coarse = 4.0;
        let dt_fine = 2.0;
        let dt_finest = 1.0;

        let final_coarse = Rk4.integrate(
            &system,
            initial.clone(),
            0.0,
            duration,
            dt_coarse,
            |_, _| {},
        );
        let final_fine = Rk4.integrate(&system, initial.clone(), 0.0, duration, dt_fine, |_, _| {});
        let final_finest = Rk4.integrate(&system, initial, 0.0, duration, dt_finest, |_, _| {});

        let err_coarse = (*final_coarse.position() - *final_finest.position()).magnitude();
        let err_fine = (*final_fine.position() - *final_finest.position()).magnitude();

        let ratio = err_coarse / err_fine;
        assert!(
            ratio > 10.0 && ratio < 25.0,
            "J2 dt convergence ratio = {ratio:.2}, expected ~16 for 4th-order (err_coarse={err_coarse:.2e}, err_fine={err_fine:.2e})"
        );
    }

    fn earth_j2_j3_j4_system() -> OrbitalSystem {
        OrbitalSystem::new(
            MU_EARTH,
            Box::new(ZonalHarmonics {
                r_body: R_EARTH,
                j2: J2_EARTH,
                j3: Some(arika::earth::J3),
                j4: Some(arika::earth::J4),
            }),
        )
    }

    #[test]
    fn j2_j3_j4_dt_convergence() {
        let system = earth_j2_j3_j4_system();
        let a = R_EARTH + 400.0;
        let i = 51.6_f64.to_radians();
        let elements = KeplerianElements {
            semi_major_axis: a,
            eccentricity: 0.0001,
            inclination: i,
            raan: 0.0,
            argument_of_periapsis: 0.0,
            true_anomaly: 0.0,
        };
        let (pos, vel) = elements.to_state_vector(MU_EARTH);
        let initial = OrbitalState::new(pos, vel);

        let duration = 1000.0;
        let dt_coarse = 4.0;
        let dt_fine = 2.0;
        let dt_finest = 1.0;

        let final_coarse = Rk4.integrate(
            &system,
            initial.clone(),
            0.0,
            duration,
            dt_coarse,
            |_, _| {},
        );
        let final_fine = Rk4.integrate(&system, initial.clone(), 0.0, duration, dt_fine, |_, _| {});
        let final_finest = Rk4.integrate(&system, initial, 0.0, duration, dt_finest, |_, _| {});

        let err_coarse = (final_coarse.position() - final_finest.position()).magnitude();
        let err_fine = (final_fine.position() - final_finest.position()).magnitude();

        let ratio = err_coarse / err_fine;
        assert!(
            ratio > 10.0 && ratio < 25.0,
            "J2+J3+J4 dt convergence ratio = {ratio:.2}, expected ~16 for 4th-order"
        );
    }

    #[test]
    fn j2_j3_j4_raan_closer_to_analytical() {
        let a = R_EARTH + 400.0;
        let i = 51.6_f64.to_radians();
        let elements = KeplerianElements {
            semi_major_axis: a,
            eccentricity: 0.0001,
            inclination: i,
            raan: 0.0,
            argument_of_periapsis: 0.0,
            true_anomaly: 0.0,
        };

        let duration = 86400.0;
        let dt = 5.0;

        let raan_j2 = propagate_raan(&earth_j2_system(), &elements, dt, duration);
        let raan_j2_j3_j4 = propagate_raan(&earth_j2_j3_j4_system(), &elements, dt, duration);

        let diff_deg = (raan_j2 - raan_j2_j3_j4).to_degrees().abs();
        assert!(
            diff_deg > 1e-4,
            "J2+J3+J4 should differ from J2-only, diff={diff_deg:.6} deg"
        );
        assert!(
            diff_deg < 1.0,
            "J3+J4 correction should be small, diff={diff_deg:.6} deg"
        );
    }
}