use cgmath::{InnerSpace, Vector3};

use super::ray::Ray;

pub struct Triangle {
    pub points: [Vector3<f32>; 3],
}

impl Triangle {
    pub fn new(v0: Vector3<f32>, v1: Vector3<f32>, v2: Vector3<f32>) -> Triangle {
        Triangle {
            points: [v0, v1, v2],
        }
    }

    // source: https://www.scratchapixel.com/lessons/3d-basic-rendering/ray-tracing-rendering-a-triangle/moller-trumbore-ray-triangle-intersection
    pub fn intersect_mt(&self, ray: &Ray, t: &mut f32) -> bool {
        let v0v1 = self.points[1] - self.points[0];
        let v0v2 = self.points[2] - self.points[0];
        let pvec = ray.direction.cross(v0v2);
        let det = v0v1.dot(pvec);

        // ray and triangle are parallel if det is close to 0
        if det.abs() < 0.001 {
            return false;
        }

        let inv_det = 1.0 / det;

        let tvec = ray.origin - self.points[0];
        let u = tvec.dot(pvec) * inv_det;

        if u < 0.0 || u > 1.0 {
            return false;
        }

        let qvec = tvec.cross(v0v1);
        let v = ray.direction.dot(qvec) * inv_det;

        if v < 0.0 || u + v > 1.0 {
            return false;
        }

        *t = v0v2.dot(qvec) * inv_det;

        true
    }
}