//
// Basic geometric things...
//
// Georg Hopp <georg@steffers.org>
//
// Copyright © 2019 Georg Hopp
//
// 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 <http://www.gnu.org/licenses/>.
//

use std::fmt::Debug;
use std::ops::{Add, Div, Mul, Neg, Sub};

use crate::math::trigonometry::Trig;
use crate::math::vector::Vector;

use super::point::Point;

#[derive(Debug, Clone)]
pub struct Face<T>
where T: Add + Sub + Neg + Mul + Div + Copy + Trig {
    corners :Vec<usize>,
    normal  :Option<Vector<T>>,
}

impl<'a, T> Face<T>
where T: Add<Output = T> + Sub<Output = T> + Neg<Output = T>
       + Mul<Output = T> + Div<Output = T>
       + PartialEq + Debug + Copy + Trig + From<i32> {
    pub fn new(corners :Vec<usize>, ps :&[Point<T>]) -> Self {
        let mut f = Face{ corners: corners, normal: None };
        f.update_normal(ps);
        f
    }

    #[inline]
    pub fn corners(&self) -> &[usize] {
        &self.corners
    }

    #[inline]
    pub fn normal(&self) -> Option<&Vector<T>> {
        (&self.normal).as_ref()
    }

    pub fn update_normal(&mut self, ps :&[Point<T>]) {
        let edge10 :Vector<T> = (ps[self.corners[1]] - ps[self.corners[0]]).into();
        let edge12 :Vector<T> = (ps[self.corners[1]] - ps[self.corners[2]]).into();
        self.normal = Some(edge10 * edge12);
    }
}