use std::cmp::Ordering;
use std::f64::consts::PI;

use crate::object::*;
use crate::util::*;

fn trace(ray: Ray, objects: &Vec<Object>) -> Option<(&Object, f64)> {
    objects
        .iter()
        .filter_map(|obj| obj.intersect(ray).map(|x| (obj, x)))
        .min_by(|a, b| a.1.partial_cmp(&b.1).unwrap_or(Ordering::Equal))
}

fn light_point(objects: &Vec<Object>, obj: &Object, point: Point3f, light: &dyn Light) -> Color {
    if light.check_shadow(point, objects) {
        let texture = obj.get_texture(point);

        light.get_color(point)
            * (texture.albedo / PI)
            * light.intensity(point)
            * obj.normal(point).dot(&*light.direction(point))
    } else {
        // Point is in shadow
        Color::black()
    }
}

pub fn cast_ray(ray: Ray, scene: &Scene) -> Color {
    if let Some((obj, dist)) = trace(ray, &scene.objects) {
        let point = ray.project(dist);
        let surface_color = obj.get_texture(point).color;

        scene
            .lights
            .iter()
            .map(|light| light_point(&scene.objects, obj, point, &**light))
            .fold(Color::black(), |acc, c| acc + c)
            * surface_color
    } else {
        scene.background
    }
}