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// std
use std::cell::Cell;
use std::sync::Arc;
// pbrt
// use crate::core::bssrdf::Bssrdf;
use crate::core::camera::Camera;
use crate::core::geometry::{vec3_abs_dot_nrmf, vec3_dot_nrmf};
use crate::core::geometry::{Bounds2i, Point2f, Ray, Vector3f};
use crate::core::integrator::uniform_sample_one_light;
use crate::core::interaction::{Interaction, MediumInteraction, SurfaceInteraction};
use crate::core::lightdistrib::create_light_sample_distribution;
use crate::core::lightdistrib::LightDistribution;
use crate::core::material::TransportMode;
use crate::core::pbrt::{Float, Spectrum};
use crate::core::reflection::BxdfType;
use crate::core::sampler::Sampler;
use crate::core::sampling::Distribution1D;
use crate::core::scene::Scene;

// see volpath.h

/// Accounts for scattering and attenuation from participating media
/// as well as scattering from surfaces - uses the render loop of a
/// [SamplerIntegrator](../../core/integrator/enum.SamplerIntegrator.html)
pub struct VolPathIntegrator {
    // inherited from SamplerIntegrator (see integrator.h)
    pub camera: Arc<Camera>,
    pub sampler: Box<Sampler>,
    pub pixel_bounds: Bounds2i,
    // see volpath.h
    pub max_depth: u32,
    pub rr_threshold: Float,           // 1.0
    pub light_sample_strategy: String, // "spatial"
    pub light_distribution: Option<Arc<LightDistribution>>,
}

impl VolPathIntegrator {
    pub fn new(
        max_depth: u32,
        camera: Arc<Camera>,
        sampler: Box<Sampler>,
        pixel_bounds: Bounds2i,
        rr_threshold: Float,
        light_sample_strategy: String,
    ) -> Self {
        VolPathIntegrator {
            camera,
            sampler,
            pixel_bounds,
            max_depth,
            rr_threshold,
            light_sample_strategy,
            light_distribution: None,
        }
    }
    pub fn preprocess(&mut self, scene: &Scene) {
        self.light_distribution =
            create_light_sample_distribution(self.light_sample_strategy.clone(), scene);
    }
    pub fn li(
        &self,
        r: &mut Ray,
        scene: &Scene,
        sampler: &mut Sampler,
        // arena: &mut Arena,
        _depth: i32,
    ) -> Spectrum {
        // TODO: ProfilePhase p(Prof::SamplerIntegratorLi);
        let mut l: Spectrum = Spectrum::default();
        let mut beta: Spectrum = Spectrum::new(1.0 as Float);
        let mut ray: Ray = Ray {
            o: r.o,
            d: r.d,
            t_max: Cell::new(r.t_max.get()),
            time: r.time,
            differential: r.differential,
            medium: r.medium.clone(),
        };
        let mut specular_bounce: bool = false;
        let mut bounces: u32 = 0_u32;
        // Added after book publication: etaScale tracks the
        // accumulated effect of radiance scaling due to rays passing
        // through refractive boundaries (see the derivation on p. 527
        // of the third edition). We track this value in order to
        // remove it from beta when we apply Russian roulette; this is
        // worthwhile, since it lets us sometimes avoid terminating
        // refracted rays that are about to be refracted back out of a
        // medium and thus have their beta value increased.
        let mut eta_scale: Float = 1.0;
        loop {
            let mut mi_opt: Option<MediumInteraction> = None;
            // intersect _ray_ with scene and store intersection in _isect_
            let mut isect: SurfaceInteraction = SurfaceInteraction::default();
            if scene.intersect(&mut ray, &mut isect) {
                // sample the participating medium, if present
                if let Some(ref medium) = ray.medium {
                    let (spectrum, option) = medium.sample(&ray, sampler);
                    beta *= spectrum;
                    if let Some(mi) = option {
                        mi_opt = Some(mi);
                    }
                }
                if beta.is_black() {
                    break;
                }
                // handle an interaction with a medium or a surface
                if let Some(mi) = mi_opt {
                    // terminate path if ray escaped or _maxDepth_ was reached
                    if bounces >= self.max_depth {
                        break;
                    }
                    let mi_p = mi.common.p;
                    // if mi.is_valid() {...}
                    if let Some(phase) = mi.clone().phase {
                        // TODO: ++volumeInteractions;
                        // handle scattering at point in medium for volumetric path tracer
                        if let Some(ref light_distribution) = self.light_distribution {
                            let distrib: Arc<Distribution1D> = light_distribution.lookup(&mi_p);
                            l += beta
                                * uniform_sample_one_light(
                                    &mi as &dyn Interaction,
                                    scene,
                                    sampler,
                                    true,
                                    Some(&distrib),
                                );
                            let mut wi: Vector3f = Vector3f::default();
                            phase.sample_p(&(-ray.d), &mut wi, sampler.get_2d());
                            ray = mi.spawn_ray(&wi);
                            specular_bounce = false;
                        }
                    }
                } else {
                    // TODO: ++surfaceInteractions;
                    // possibly add emitted light at intersection
                    if bounces == 0 || specular_bounce {
                        // add emitted light at path vertex
                        l += beta * isect.le(&-ray.d);
                    }
                    // terminate path if _maxDepth_ was reached
                    if bounces >= self.max_depth {
                        break;
                    }
                    // compute scattering functions and skip over medium boundaries
                    let mode: TransportMode = TransportMode::Radiance;
                    isect.compute_scattering_functions(&ray, true, mode);
                    if let Some(ref _bsdf) = isect.bsdf {
                        // we are fine (for below)
                    } else {
                        ray = isect.spawn_ray(&ray.d);
                        // bounces--;
                        continue;
                    }
                    if let Some(ref light_distribution) = self.light_distribution {
                        let light_distrib: Arc<Distribution1D> =
                            light_distribution.lookup(&isect.common.p);
                        // Sample illumination from lights to find
                        // attenuated path contribution.
                        let it: &SurfaceInteraction = &isect;
                        l += beta
                            * uniform_sample_one_light(
                                it,
                                scene,
                                sampler,
                                true,
                                Some(&light_distrib),
                            );
                        if let Some(ref bsdf) = isect.bsdf {
                            // Sample BSDF to get new path direction
                            let wo: Vector3f = -ray.d;
                            let mut wi: Vector3f = Vector3f::default();
                            let mut pdf: Float = 0.0 as Float;
                            let bsdf_flags: u8 = BxdfType::BsdfAll as u8;
                            let mut sampled_type: u8 = u8::max_value(); // != 0
                            let f: Spectrum = bsdf.sample_f(
                                &wo,
                                &mut wi,
                                &sampler.get_2d(),
                                &mut pdf,
                                bsdf_flags,
                                &mut sampled_type,
                            );
                            if f.is_black() || pdf == 0.0 as Float {
                                break;
                            }
                            beta *= (f * vec3_abs_dot_nrmf(&wi, &isect.shading.n)) / pdf;
                            assert!(
                                !(beta.y().is_infinite()),
                                "[{:#?}, {:?}] = ({:#?} * dot({:#?}, {:#?})) / {:?}",
                                sampler.get_current_pixel(),
                                sampler.get_current_sample_number(),
                                f,
                                wi,
                                isect.shading.n,
                                pdf
                            );
                            specular_bounce = (sampled_type & BxdfType::BsdfSpecular as u8) != 0_u8;
                            if ((sampled_type & BxdfType::BsdfSpecular as u8) != 0_u8)
                                && ((sampled_type & BxdfType::BsdfTransmission as u8) != 0_u8)
                            {
                                let eta: Float = bsdf.eta;
                                // Update the term that tracks radiance
                                // scaling for refraction depending on
                                // whether the ray is entering or leaving
                                // the medium.
                                if vec3_dot_nrmf(&wo, &isect.common.n) > 0.0 as Float {
                                    eta_scale *= eta * eta;
                                } else {
                                    eta_scale *= 1.0 as Float / (eta * eta);
                                }
                            }
                            ray = isect.spawn_ray(&wi);
                            // account for attenuated subsurface scattering, if applicable
                            if let Some(ref bssrdf) = isect.bssrdf {
                                if (sampled_type & BxdfType::BsdfTransmission as u8) != 0_u8 {
                                    // importance sample the BSSRDF
                                    let s2: Point2f = sampler.get_2d();
                                    let s1: Float = sampler.get_1d();
                                    let (s, pi_opt) = bssrdf.sample_s(
                                        // the next three (extra) parameters are used for SeparableBssrdfAdapter
                                        bssrdf.clone(),
                                        bssrdf.mode,
                                        bssrdf.eta,
                                        // done
                                        scene,
                                        s1,
                                        s2,
                                        &mut pdf,
                                    );
                                    if s.is_black() || pdf == 0.0 as Float {
                                        break;
                                    }
                                    assert!(!(beta.y().is_infinite()));
                                    beta *= s / pdf;
                                    if let Some(pi) = pi_opt {
                                        // account for the direct subsurface scattering component
                                        let distrib: Arc<Distribution1D> =
                                            light_distribution.lookup(&pi.common.p);
                                        l += beta
                                            * uniform_sample_one_light(
                                                &pi,
                                                scene,
                                                sampler,
                                                true,
                                                Some(&distrib),
                                            );
                                        // account for the indirect subsurface scattering component
                                        let mut wi: Vector3f = Vector3f::default();
                                        let mut pdf: Float = 0.0 as Float;
                                        let bsdf_flags: u8 = BxdfType::BsdfAll as u8;
                                        let mut sampled_type: u8 = u8::max_value(); // != 0
                                        if let Some(ref bsdf) = pi.bsdf {
                                            let f: Spectrum = bsdf.sample_f(
                                                &pi.common.wo,
                                                &mut wi,
                                                &sampler.get_2d(),
                                                &mut pdf,
                                                bsdf_flags,
                                                &mut sampled_type,
                                            );
                                            if f.is_black() || pdf == 0.0 as Float {
                                                break;
                                            }
                                            beta *= f * vec3_abs_dot_nrmf(&wi, &pi.shading.n) / pdf;
                                            assert!(!(beta.y().is_infinite()));
                                            specular_bounce = (sampled_type
                                                & BxdfType::BsdfSpecular as u8)
                                                != 0_u8;
                                            ray = pi.spawn_ray(&wi);
                                        } else {
                                            panic!("no pi.bsdf found");
                                        }
                                    } else {
                                        panic!("bssrdf.sample_s() did return (s, None)");
                                    }
                                }
                            }
                        } else {
                            println!("TODO: if let Some(ref bsdf) = isect.bsdf failed");
                        }
                    }
                }
                // Possibly terminate the path with Russian roulette.
                // Factor out radiance scaling due to refraction in rr_beta.
                let rr_beta: Spectrum = beta * eta_scale;
                if rr_beta.max_component_value() < self.rr_threshold && bounces > 3 {
                    let q: Float =
                        (0.05 as Float).max(1.0 as Float - rr_beta.max_component_value());
                    if sampler.get_1d() < q {
                        break;
                    }
                    beta /= 1.0 as Float - q;
                    assert!(!(beta.y().is_infinite()));
                }
            } else {
                // sample the participating medium, if present
                if let Some(ref medium) = ray.medium {
                    let (spectrum, option) = medium.sample(&ray, sampler);
                    beta *= spectrum;
                    if let Some(mi) = option {
                        mi_opt = Some(mi);
                    }
                }
                if beta.is_black() {
                    break;
                }
                // handle an interaction with a medium
                if let Some(mi) = mi_opt {
                    // terminate path if ray escaped or _maxDepth_ was reached
                    if bounces >= self.max_depth {
                        break;
                    }
                    let mi_p = mi.common.p;
                    // if mi.is_valid() {...}
                    if let Some(phase) = mi.clone().phase {
                        // TODO: ++volumeInteractions;
                        // handle scattering at point in medium for volumetric path tracer
                        if let Some(ref light_distribution) = self.light_distribution {
                            let distrib: Arc<Distribution1D> = light_distribution.lookup(&mi_p);
                            l += beta
                                * uniform_sample_one_light(
                                    &mi as &dyn Interaction,
                                    scene,
                                    sampler,
                                    true,
                                    Some(&distrib),
                                );
                            let mut wi: Vector3f = Vector3f::default();
                            phase.sample_p(&(-ray.d), &mut wi, sampler.get_2d());
                            ray = mi.spawn_ray(&wi);
                            specular_bounce = false;
                        }
                    }
                }
                // add emitted light from the environment
                if bounces == 0 || specular_bounce {
                    for light in &scene.infinite_lights {
                        l += beta * light.le(&mut ray);
                    }
                }
                // terminate path if ray escaped
                break;
            }
            bounces += 1_u32;
        }
        l
    }
    pub fn get_camera(&self) -> Arc<Camera> {
        self.camera.clone()
    }
    pub fn get_sampler(&self) -> &Sampler {
        &self.sampler
    }
    pub fn get_pixel_bounds(&self) -> Bounds2i {
        self.pixel_bounds
    }
}