use crate::calculus::calculus::{Ray, Vec3};
use crate::global::{DisplayBuffer, Pixel, CAMERA_CENTER, FOCAL_LENGTH, IMG_HEIGHT, IMG_WIDTH, VIEWPORT_HEIGHT, VIEWPORT_WIDTH};

fn ray_color(ray: &Ray) -> Vec3 {
    let unit_direction = ray.direction.unit();
    let a = 0.5 * (unit_direction.y + 1.0);
    let vec_1 = Vec3 { x:1.0, y: 1.0, z: 1.0 };
    let vec_2 = Vec3 { x: 0.5, y: 0.7, z: 1.0 };
    vec_1.scalar_mul(1.0 - a)
        .add(&vec_2.scalar_mul(a))
}

pub fn render(display_buffer: &mut DisplayBuffer) {
    let viewport_hor_vector = Vec3{ x: VIEWPORT_WIDTH as f32, y: 0.0, z: 0.0 };
    let viewport_ver_vector = Vec3 { x: 0.0, y: -1f32 * VIEWPORT_HEIGHT as f32, z: 0.0 };

    let delta_pixel_u = viewport_hor_vector.scalar_mul(1.0 / VIEWPORT_WIDTH as f32);
    let delta_pixel_v = viewport_ver_vector.scalar_mul(1.0 / VIEWPORT_WIDTH as f32);

    let viewport_upper_left = CAMERA_CENTER
        .sub(&Vec3 { x: 0f32, y: 0f32, z: FOCAL_LENGTH})
        .sub(&viewport_hor_vector.scalar_mul(0.5))
        .sub(&viewport_ver_vector.scalar_mul(0.5));
    let pixel_upper_left = viewport_upper_left.add(
        &delta_pixel_u.add(&delta_pixel_u).scalar_mul(0.5)
    );

    (0..IMG_HEIGHT).for_each(|j| {
        (0..IMG_WIDTH).for_each(|i| {
            let pixel_center = pixel_upper_left
                .add(&delta_pixel_u.scalar_mul(i as f32))
                .add(&delta_pixel_v.scalar_mul(j as f32));
            let ray_direction = pixel_center.sub(&CAMERA_CENTER);
            let ray = Ray {
                origin: &CAMERA_CENTER,
                direction: &ray_direction,
            };
            let Vec3 {x, y, z} = ray_color(&ray);
            display_buffer[j][i] = Pixel::from_frac(x, y, z);
        })
    })
}