#include <iostream>
#include <cmath>

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

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 disciminant = half_b*half_b - a*c;
    if (disciminant < 0) {
        return -1.0;
    } else {
        return (-half_b - std::sqrt(disciminant)) / a;
    }
}

Color ray_color(const Ray& r) {
    auto sphere_center = Point3(0, 0, -1);
    auto t = hit_sphere(sphere_center, 0.5, r);
    if (t > 0.0) {
        Vec3 n = unit_vector(r.at(t) - sphere_center);
        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() {
    const auto aspect_ratio = 16.0 / 9.0;
    const int image_width = 1280;
    const int image_height = static_cast<int>(image_width / aspect_ratio);

    std::cout << "P3\n" << image_width << " " << image_height << "\n255\n";

    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);

    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";
}