/*
 * Copyright (C) 2026 Richard
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
#include "color.h"
#include "ray.h"
#include "vec3.h"

#include <iostream>

double hit_sphere( const point3& center, double radius, const ray& r )
{
  vec3 oc = center - r.origin();
  auto a = dot( r.direction(), r.direction() );
  auto b = -2.0 * dot( r.direction(), oc );
  auto c = dot( oc, oc ) - radius * radius;
  auto discriminant = b * b - 4 * a * c;

  if ( discriminant < 0 ) {
    return -1.0;
  } else {
    return ( -b - std::sqrt( discriminant ) ) / ( 2.0 * 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() );
  auto a = 0.5 * ( unit_direction.y() + 1.0 );
  return ( 1.0 - a ) * color( 1.0, 1.0, 1.0 ) + a * color( 0.5, 0.7, 1.0 );
}

int main()
{
  // Image

  auto aspect_ratio = 16.0 / 9.0;
  const int image_width = 400;
  // Calculate the image height, and ensure that it's at least 1.
  int image_height = static_cast<int>( image_width / aspect_ratio );
  image_height = ( image_height < 1 ) ? 1 : image_height;

  // Camera
  auto focal_length = 1.0;
  auto viewport_height = 2.0;
  auto viewport_width = viewport_height * ( double( image_width ) / image_height );
  auto camera_center = point3( 0, 0, 0 );

  // Calculate the vectors across the horizontal and down the vertical viewport edges.
  auto viewport_u = vec3( viewport_width, 0, 0 );
  auto viewport_v = vec3( 0, -viewport_height, 0 );

  // Calculate the horizontal and vertical delta vectors from pixel to pixel.
  auto pixel_delta_u = viewport_u / image_width;
  auto pixel_delta_v = viewport_v / image_height;

  // Calculate the location of the upper left pixel.
  auto viewport_upper_left = camera_center - vec3( 0, 0, focal_length ) - viewport_u / 2 - viewport_v / 2;
  auto pixel00_loc = viewport_upper_left + 0.5 * ( pixel_delta_u + pixel_delta_v );

  // Render

  std::cout << "P3\n" << image_width << " " << image_height << "\n255\n";
  for ( int j = 0; j < image_height; j++ ) {
    std::clog << "\rScanlines remaining: " << ( image_height - j ) << ' ' << std::flush;
    for ( int i = 0; i < image_width; i++ ) {
      auto pixel_center = pixel00_loc + ( i * pixel_delta_u ) + ( j * pixel_delta_v );
      auto ray_direction = pixel_center - camera_center;
      ray r( camera_center, ray_direction );

      const color pixel_color = ray_color( r );
      write_color( std::cout, pixel_color );
    }
  }
  std::clog << "\rDone.                 \n";
  return 0;
}