mod color;
mod ray;
mod vec3;
use ray::Ray;
use std::env;
use std::fs::File;
use std::io::BufWriter;
use std::io::Write;
use vec3::Color;
use vec3::Point3;
use vec3::Vec3;

fn hit_sphere(center: &Point3, radius: f64, r: &Ray) -> f64 {
    let oc = r.origin() - *center;
    let a = Vec3::dot(r.direction(), r.direction());
    let b = 2.0 * Vec3::dot(oc, r.direction());
    let c = Vec3::dot(oc, oc) - radius * radius;
    let discriminant = b * b - 4.0 * a * c;

    if discriminant < 0.0 {
        return -1.0;
    } else {
        return (-b - discriminant.sqrt()) / (2.0 * a);
    }
}

fn ray_color(r: &Ray) -> Color {
    let t = hit_sphere(&Point3::new(0.0, 0.0, -1.0), 0.5, r);
    if t > 0.0 {
        let n = Vec3::unit_vector(r.at(t) - Vec3::new(0.0, 0.0, -1.0));
        return 0.5 * Color::new(n.x() + 1.0, n.y() + 1.0, n.z() + 1.0);
    }

    let unit_direction = r.direction();
    let t = 0.5 * (unit_direction.y() + 1.0);
    return (1.0 - t) * Color::new(1.0, 1.0, 1.0) + t * Color::new(0.5, 0.7, 1.0);
}

fn main() {
    // File
    let mut default_file = "image.ppm";

    // Image
    let aspect_ratio = 16.0 / 9.0;
    let image_width = 400;
    let image_height = (image_width as f64 / aspect_ratio) as u64;

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

    let origin = Point3::new(0.0, 0.0, 0.0);
    let horizontal = Vec3::new(viewport_width, 0.0, 0.0);
    let vertical = Vec3::new(0.0, viewport_height, 0.0);
    let lower_left_corner =
        origin - horizontal / 2.0 - vertical / 2.0 - Vec3::new(0.0, 0.0, focal_length);

    // Render
    let args: Vec<String> = env::args().collect();
    if args.len() > 1 && args[1] != "" {
        default_file = &args[1];
    }
    let mut file = BufWriter::new(File::create(default_file).unwrap());
    writeln!(&mut file, "P3\n{image_width} {image_height}\n255\n").unwrap();

    for j in (0..image_height).rev() {
        eprint!("\rScanlines remaining: {j:5}");
        for i in 0..image_width {
            let u = i as f64 / (image_width - 1) as f64;
            let v = j as f64 / (image_height - 1) as f64;
            let r = Ray::new(
                origin,
                lower_left_corner + u * horizontal + v * vertical - origin,
            );
            let pixel_color = ray_color(&r);

            color::write_color(&mut file, pixel_color);
        }
    }
    eprintln!("\nDone!");
}