#include "camera.h"

#include "ray.h"
#include "rng.h"

#include <float.h>
#include <stdio.h>

#define MAX_ITER 10
#define MIN_T 1e-6
#define NSAMPLES 100

static const vec3_t lightblue = { 0.4, 0.6, 1.0 };
static const vec3_t white = { 1.0, 1.0, 1.0 };
static const vec3_t black = { 0.0, 0.0, 0.0 };

static ray_t scatter(hit_t hit)
{
	const vec3_t rand = rng_vec3();
	const vec3_t dir
	    = vec3_dot(rand, hit.normal) > 0.0 ? rand : vec3_scale(rand, -1.0);
	return (ray_t) { .orig = hit.point, .dir = dir };
}

static vec3_t trace(ray_t ray, const obj_t *scene, unsigned scene_count)
{
	double coeff = 1.0;
	for (unsigned i = 0; i < MAX_ITER; ++i) {
		hit_t hit = { .t = DBL_MAX };
		for (unsigned j = 0; j < scene_count; ++j)
			scene[j].intersect(scene[j].params, ray, &hit, MIN_T, hit.t);

		if (hit.t == DBL_MAX) {
			const double a = (ray.dir.y + 1.0) / 2.0;
			return vec3_scale(
			    vec3_add(vec3_scale(lightblue, a), vec3_scale(white, 1 - a)),
			    coeff);
		}

		ray = scatter(hit);
		coeff *= 0.5;
	}

	return black;
}

static void setpix(vec3_t col, pix_t *out)
{
	out->r = UINT16_MAX * col.x;
	out->g = UINT16_MAX * col.y;
	out->b = UINT16_MAX * col.z;
	out->a = UINT16_MAX;
}

camera_t camera_init(
    vec3_t pos, double focal_len, double viewport_height, uint32_t img_width,
    uint32_t img_height)
{
	const double aspect = (double)img_width / (double)img_height;
	const double viewport_width = viewport_height * aspect;
	const vec3_t viewport_disp = { 0, 0, focal_len };
	const vec3_t u = { viewport_width, 0, 0 };
	const vec3_t v = { 0, -viewport_height, 0 };
	const vec3_t topleft = vec3_sub(
	    vec3_sub(pos, viewport_disp), vec3_scale(vec3_add(u, v), 0.5));

	const vec3_t x_step = vec3_scale(u, 1.0 / (double)img_width);
	const vec3_t y_step = vec3_scale(v, 1.0 / (double)img_height);
	const vec3_t pix_origin
	    = vec3_add(topleft, vec3_scale(vec3_add(x_step, y_step), 0.5));

	return (camera_t) {
		.pos = pos,
		.pix_origin = pix_origin,
		.x_step = x_step,
		.y_step = y_step,
		.img_width = img_width,
		.img_height = img_height,
	};
}

void camera_render(
    const camera_t *camera, const obj_t *scene, unsigned scene_count,
    img_t *img_out)
{
	const uint32_t w = img_out->w = camera->img_width;
	const uint32_t h = img_out->h = camera->img_height;

	for (unsigned y = 0; y < h; ++y) {
		fprintf(stderr, "\r[%3d/%3d]", y, h);
		fflush(stderr);

		const vec3_t row
		    = vec3_add(camera->pix_origin, vec3_scale(camera->y_step, y));
		for (unsigned x = 0; x < w; ++x) {
			const vec3_t pix = vec3_add(row, vec3_scale(camera->x_step, x));
			const ray_t ray = {
				.orig = camera->pos,
				.dir = vec3_unit(pix),
			};

			vec3_t colour = black;
			for (unsigned i = 0; i < NSAMPLES; ++i) {
				const double weight = 1.0 / NSAMPLES;
				const vec3_t sample = trace(ray, scene, scene_count);
				colour = vec3_add(colour, vec3_scale(sample, weight));
			}

			setpix(colour, img_out->pix + (w * y + x));
		}
	}

	fprintf(stderr, "\r[%3d/%3d]\n", h, h);
}