/* scene.c
 *
 * Definition of Scene-related functions.
 *
 * Eryn Wells <eryn@erynwells.me>
 */

#include <chrono>
#include <cmath>
#include <cstdio>

#include "basics.h"
#include "light.h"
#include "object.h"
#include "scene.h"
#include "writer.h"


Scene::Scene()
    : width(640), height(480),
      max_depth(5),
      min_weight(1e-4),
      ambient(new AmbientLight()),
      shapes(),
      lights(),
      nrays(0),
      pixels(NULL)
{ }


Scene::~Scene()
{
    if (ambient != NULL) {
        delete ambient;
    }

    for (Shape *s : shapes) {
        delete s;
    }
    shapes.clear();

    for (PointLight *l : lights) {
        delete l;
    }
    lights.clear();

    if (pixels != NULL) {
        delete[] pixels;
        _is_rendered = false;
    }
}


bool
Scene::is_rendered()
    const
{
    return _is_rendered;
}


int
Scene::get_width()
    const
{
    return width;
}


int
Scene::get_height()
    const
{
    return height;
}


AmbientLight &
Scene::get_ambient()
    const
{
    return *ambient;
}


const Color *
Scene::get_pixels()
    const
{
    return pixels;
}


/*
 * scene_load --
 *
 * Load scene objects into this Scene from the given file.
 */
void
Scene::read(const std::string &filename)
{ }


/*
 * scene_save --
 *
 * Write a rendered scene to the given file.
 */
void
Scene::write(Writer &writer, const std::string &filename)
{
    writer.write_scene(*this, filename);
}


/*
 * Scene::render --
 *
 * Render the given Scene.
 */
void
Scene::render()
{
    std::chrono::time_point<std::chrono::system_clock> start, end;
    start = std::chrono::system_clock::now();

    pixels = new Color[width * height];

    Ray primary_ray;
    Vector3 o, d;
    for (int y = 0; y < height; y++) {
        for (int x = 0; x < width; x++) {
            // Assemble a ray and trace it.
            o = Vector3(x, y, -1000);
            d = Vector3(0, 0, 1);
            d.normalize();
            primary_ray = Ray(o, d);
            Color c = trace_ray(primary_ray);
            pixels[y * width + x] = c;
        }
    }

    end = std::chrono::system_clock::now();
    std::chrono::duration<float> seconds = end - start;

    _is_rendered = true;
    printf("Scene rendered. %d rays traced in %f seconds.\n", nrays, seconds.count());
}


/*
 * Scene::add_shape --
 *
 * Add a shape to the scene.
 */
void
Scene::add_shape(Shape *shape)
{
    shapes.push_back(shape);
}


/*
 * Scene::add_light --
 *
 * Add a light to the scene.
 */
void
Scene::add_light(PointLight *light)
{
    lights.push_back(light);
}


/*
 * Scene::trace_ray --
 *
 * Trace the given ray through the scene, recursing until depth has been reached.
 */
Color
Scene::trace_ray(const Ray &ray,
                 const int depth,
                 const float weight)
{
    if (depth >= max_depth || weight <= min_weight) {
        return Color::Black;
    }

    Color out_color = Color::Black;
    Shape *intersected_shape = NULL;
    float *t = NULL;
    float nearest_t = INFINITY;
    int nints;

    // Keep stats.
    nrays++;

    // Find intersections of this ray with objects in the scene.
    for (Shape *s : shapes) {
        nints = s->does_intersect(ray, &t);
        if (nints > 0) {
            for (int i = 0; i < nints; i++) {
                if (t[i] < 1e-2) {
                    break;
                }
                if (t[i] < nearest_t) {
                    intersected_shape = s;
                    nearest_t = t[i];
                }
            }
            delete[] t;
        }
    }

    // If there was no intersection, return black.
    if (intersected_shape == NULL) {
        return out_color;
    }

    Material shape_material = intersected_shape->get_material();
    Color shape_color = shape_material.get_diffuse_color();

    Vector3 intersection = ray.parameterize(nearest_t);
    Vector3 normal = intersected_shape->compute_normal(intersection);

    /*
     * Diffuse lighting. (Shading, etc.)
     */

    Vector3 light_direction;
    float ldotn, diffuse_level, ambient_level;
    Ray shadow_ray;

    for (PointLight *l : lights) {
        light_direction = (intersection - l->get_origin()).normalize();
        ldotn = light_direction.dot(normal);

        if (ldotn < 0) {
            ldotn = 0.0;
        }

        diffuse_level = shape_material.get_diffuse_level();
        ambient_level = 1.0 - diffuse_level;

        shadow_ray = Ray(intersection, light_direction);
        for (Shape *s : shapes) {
            // Skip the intersected shape.
            if (s == intersected_shape) {
                continue;
            }

            // Figure out if we're in shadow.
            if (s->does_intersect(shadow_ray, NULL) > 0) {
                diffuse_level = 0.0;
                break;
            }
        }

        /*
         * Compute basic Lambert diffuse shading for this object.
         */
        out_color += shape_color * (  ambient_level * ambient->compute_color_contribution()
                                    + diffuse_level * ldotn);
    }

    /*
     * Specular lighting. (Reflections, etc.)
     */

    float specular_level = shape_material.get_specular_level();
    const Color &specular_color = shape_material.get_specular_color();

    /*
     * Compute the reflection ray. Computing the direction of the reflection ray is done by the following formula:
     *
     *     d = dr - 2n(dr . n)
     *
     * where d is the direction, dr is the direction of the incoming ray, and n is the normal vector. Period (.)
     * indicates the dot product.
     *
     * The origin of the reflection ray is the point on the surface where the incoming ray intersected with it.
     */
    Ray reflection_ray = Ray(intersection, ray.direction - 2.0 * normal * ray.direction.dot(normal));
    Color reflection_color = trace_ray(reflection_ray, depth + 1, weight * specular_level);

    // TODO: Mix in specular_color of material.
    out_color += specular_level * specular_color * reflection_color;

    return out_color;
}