#include <stdio.h>
#include <stdint.h>

#include "vec3.hpp"
#include "color.hpp"
#include "ray.hpp"

color ray_color(const ray& r);
double hit_sphere(const point3& center, double radius, const ray& r);

color ray_color(const ray& r)
{
    double t = hit_sphere(point3(0,0,-1), 0.5, r);
    if (t > 0.0)
    {
        vec3 N = normalize(r.at(t) - vec3(0,0,-1));
        return 0.5*color(N.x+1, N.y+1, N.z+1);
    }
    vec3 unit_direction = normalize(r.direction);
    t = 0.5*(unit_direction.y + 1.0);
    
    return (1-t) * color(1,1,1) + t*color(0.5, 0.7, 1.0);
}

double hit_sphere(const point3& center, double radius, const ray& r)
{
    vec3 oc = r.origin - center;
    double a = dot(r.direction, r.direction);
    double b = 2.0 * dot(oc, r.direction);
    double c = dot(oc,oc) - radius*radius;
    double discriminant = b*b - 4*a*c;
    if (discriminant < 0)
        return -1;
    else
        return (-b - sqrt(discriminant)) / (2.0*a);
}

int main()
{
    // Image
    double aspect_ratio = 16.0 / 9;
    const int32_t image_width = 400;
    const int32_t image_height = (int32_t) (image_width / aspect_ratio);

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

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

    // Render
    printf("P3\n%d %d\n255\n", image_width, image_height);

    for (int32_t j = image_height - 1; j >= 0; --j)
    {
        fprintf(stderr, "\rScanlines remaining: %d ", j);
        fflush(stderr);
        for (int32_t i = 0; i < image_width; ++i)
        {
            double u = (double)i / (image_width-1);
            double v = (double)j / (image_height-1);            
            ray r = ray(origin, lower_left_corner + u*horizontal + v*vertical - origin);            
            color pixel_color = ray_color(r);
            
            write_color(stdout, pixel_color);
        }        
    }
    fprintf(stderr, "\nDone\n");
}