src/cube.rs


use core::f64;

use alg_tools::loc::Loc;
use alg_tools::norms::{Norm, L2};
use crate::manifold::ManifoldPoint;

#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub enum Face {F1, F2, F3, F4, F5, F6}
use Face::*;

pub type Point = Loc<f64, 2>;

pub type AdjacentFaces = [Face; 4];

#[derive(Clone, Debug)]
pub enum Path {
    Direct { destination : Face },
    Indirect { destination : Face, intermediate : Face },
}

/// An iterator over paths on a cube, from a source face to a destination face.
#[derive(Clone, Debug)]
pub enum PathIter {
    Direct(Face),
    Indirect{ destination : Face, intermediate : AdjacentFaces, current : usize},
    Exhausted,
}

impl std::iter::Iterator for PathIter {
    type Item = Path;
    
    fn next(&mut self) -> Option<Self::Item> {
        use PathIter::*;
        match self {
            &mut Exhausted => None,
            &mut Direct(destination) => {
                *self = Exhausted;
                Some(Path::Direct { destination })
            },
            &mut Indirect{destination, intermediate : ref i, ref mut current} => {
                if *current < i.len() {
                    let intermediate = i[*current];
                    *current += 1;
                    Some(Path::Indirect{ destination, intermediate })
                } else {
                    *self = Exhausted;
                    None
                }
            }
        }
    }
}


impl Face {
    /// Returns an array of the four faces adjacent to `self` in the
    /// order [left, right, down, up] in the `self`-relative unfolding.
    pub fn adjacent_faces(&self) -> AdjacentFaces {
        match *self {
            F1 => [F3, F2, F4, F5],
            F2 => [F4, F5, F1, F6],
            F3 => [F5, F4, F1, F6],
            F4 => [F3, F2, F1, F6],
            F5 => [F2, F3, F1, F6],
            F6 => [F3, F2, F4, F5],
        }
    }

    /// Returns the face opposing `self`.
    pub fn opposing_face(&self) -> Face {
        match *self {
            F1 => F6,
            F2 => F3,
            F3 => F2,
            F4 => F5,
            F5 => F4,
            F6 => F1,
        }
    }

    /// Converts a point on an adjacent face to the coordinate system of `self`.
    pub fn convert_adjacent(&self, adjacent : Face, p: &Point) -> Option<Point> {
        let Loc([x, y]) = *p;
        let mk = |x, y| Some(Loc([x, y]));
        match adjacent {
            F1 =>  match *self {
                F2 => mk(y, x - 1.0),
                F3 => mk(1.0 - y, -x),
                F4 => mk(x, -y),
                F5 => mk(1.0 - x, y - 1.0),
                F1 => mk(x, y),
                F6 => None,
            },
            F2 => match *self {
                F1 => mk(y + 1.0, x),
                F4 => mk(x + 1.0, y),
                F5 => mk(x - 1.0, y),
                F6 => mk(2.0 - y, x),
                F2 => mk(x, y),
                F3 => None,
            },
            F3 => match *self {
                F1 => mk(-y, 1.0 - x),
                F4 => mk(x - 1.0, y),
                F5 => mk(x + 1.0, y),
                F6 => mk(y - 1.0, 1.0 - x),
                F3 => mk(x, y),
                F2 => None,
            },
            F4 => match *self {
                F1 => mk(x, -y),
                F2 => mk(x - 1.0, y),
                F3 => mk(x + 1.0, y),
                F6 => mk(x, y - 1.0),
                F4 => mk(x, y),
                F5 => None,
            },
            F5 => match *self {
                F1 => mk(1.0 -x, y + 1.0),
                F2 => mk(x + 1.0, y),
                F3 => mk(x - 1.0, y),
                F6 => mk(1.0 -x, 2.0 - y),
                F5 => mk(x, y),
                F4 => None,
            },
            F6 => match *self {
                F2 => mk(y, 2.0 - x),
                F3 => mk(1.0 - y, x + 1.0),
                F4 => mk(x, y + 1.0),
                F5 => mk(1.0 - x, 2.0 - y),
                F6 => mk(x, y),
                F1 => None,
            }
        }
    }

    /// Converts a point behind a path to the coordinate system of `self`.
    pub fn convert(&self, path : &Path, p: &Point) -> Point {
        use Path::*;
        //dbg!(*self, path);
        match path {
            &Direct{ destination : d} => self.convert_adjacent(d, p),
            &Indirect{ destination : d, intermediate : i }
                => {self.convert_adjacent(i, &i.convert_adjacent(d, p).unwrap())}
        }.unwrap()
    }


    /// Returns an iterator over all the paths from `self` to `other`.
    fn paths(&self, other : Face) -> PathIter {
        //dbg!(self, other);
        if self.opposing_face() == other {
            PathIter::Indirect {
                intermediate : self.adjacent_faces(),
                destination : other,
                current : 0
            }
        } else {
            PathIter::Direct(other)
        }
    }

    pub fn is_in_face(&self, p: &Point) -> bool {
        p.iter().map(|t| t.abs()).all(|t| 0.0 <= t && t <= 1.0)
    }

    pub fn find_crossing(&self, p : &Point) -> Face {
        let &Loc([x, y]) = p;
        use std::cmp::Ordering::*;
        let crossing = |t| match (0.0 <= t, t<=1.0) {
            (false, _) => Less,
            (_, false) => Greater,
            _ => Equal,
        };

        // TODO: how to properly handle corners? Just throw an error?
        match (crossing(x), crossing(y)) {
            (Equal, Equal) => *self,
            (Less, _) => self.adjacent_faces()[0],
            (Greater, _) => self.adjacent_faces()[1],
            (Equal, Less) => self.adjacent_faces()[2],
            (Equal, Greater) => self.adjacent_faces()[3],
        }
    }
}

#[derive(Clone, Debug, PartialEq)]
pub struct OnCube {
    face : Face,
    point : Point,
}

impl ManifoldPoint for OnCube {
    type Tangent = Point;

    fn exp(&self, tangent : &Self::Tangent) -> Self {
        let mut face = self.face;
        let mut point = self.point + tangent;
        loop {
            let next_face = face.find_crossing(&point);
            if next_face == face {
                break
            }
            point = next_face.convert_adjacent(face, &point).unwrap();
            face = next_face;
        }
        OnCube { face, point }
    }

    fn log(&self, other : &Self) -> Self::Tangent {
        let mut best_len = f64::INFINITY;
        let mut best_tan = Loc([0.0, 0.0]);
        for path in self.face.paths(other.face) {
            let tan = self.face.convert(&path, &other.point) - &self.point;
            let len = tan.norm(L2);
            if len < best_len {
                best_tan = tan;
                best_len = len;
            }
        }
        best_tan
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn log_test_adjacent() {
        let p1 = OnCube{ face : F1, point : Loc([0.5, 0.5])};
        let p2 = OnCube{ face : F2, point : Loc([0.5, 0.5])};

        assert_eq!(p1.log(&p2).norm(L2), 1.0);
    }

    #[test]
    fn log_test_opposing_equal() {
        let p1 = OnCube{ face : F1, point : Loc([0.5, 0.5])};
        let p2 = OnCube{ face : F6, point : Loc([0.5, 0.5])};

        assert_eq!(p1.log(&p2).norm(L2), 2.0);
    }

    #[test]
    fn log_test_opposing_unique_shortest() {
        let p1 = OnCube{ face : F1, point : Loc([0.3, 0.25])};
        let p2 = OnCube{ face : F6, point : Loc([0.3, 0.25])};

        assert_eq!(p1.log(&p2).norm(L2), 1.5);
    }
}