#include "color.h"
#include "ray.h"
#include "vec3.h"

#include <iostream>

double hit_sphere(const point3& center, double radius, const ray& r) {
	vec3 oc = r.origin() - center;
	auto a = r.direction().length_squared();
	auto half_b = dot(oc, r.direction());
	auto c = oc.length_squared() - radius*radius;
	auto discriminant = half_b*half_b - a*c;

	if (discriminant < 0) {
		return -1.0;
	} else {
		return (-half_b - sqrt(discriminant)) / a;
	}
}

color ray_color(const ray& r) {
	auto t = hit_sphere(point3(0, 0, -1), 0.5, r);
	if (t > 0.0) {
		vec3 N = unit_vector(r.at(t) - vec3(0, 0, -1));
		return 0.5*color(N.x()+1, N.y()+1, N.z()+1);
	}

	vec3 unit_direction = unit_vector(r.direction());
	t = 0.5*(unit_direction.y() + 1.0);
	return (1.0 - t)*color(1.0, 1.0, 1.0) + t*color(0.5, 0.7, 1.0);
}

int main() {
	// Image
	const auto aspect_ratio = 16.0 / 9.0;
	const int image_width = 400;
	const int image_height = static_cast<int>(image_width / aspect_ratio);

	// Camera
	auto viewport_height = 2.0;
	auto viewport_width = aspect_ratio * viewport_height;
	auto focal_length = 1.0;

	auto origin = point3(0, 0, 0);
	auto horizontal = vec3(viewport_width, 0, 0);
	auto vertical = vec3(0, viewport_height, 0);
	auto lower_left_corner = origin - horizontal/2 - vertical/2 - vec3(0, 0, focal_length);

	// Render
	std::cout<<"P3\n"<<image_width<<" "<<image_height<<"\n255\n";
	for (int j = image_height-1; j >= 0; --j) {
		std::cerr<<"\rScanlines remaining: "<<j<<" "<<std::flush;
		for (int i = 0; i < image_width; ++i) {
			auto u = double(i) / (image_width-1);
			auto v = double(j) / (image_height-1);
			ray r(origin, lower_left_corner + u*horizontal + v*vertical - origin);
			color pixel_color = ray_color(r);
			write_color(std::cout, pixel_color);
		}
	}
	std::cerr<<"\nDone.\n";
}