pyramix/src/state.rs

use std::fmt::{Display, Formatter};
use std::ops::Add;

#[derive(Copy, Clone, Debug, Hash, PartialOrd, Ord, PartialEq, Eq)]
pub struct State {
    pub edges: [(u8, bool); 6],
    pub corners: [u8; 4],
}

impl Default for State {
    fn default() -> Self {
        Self {
            edges: [
                (0, false),
                (1, false),
                (2, false),
                (3, false),
                (4, false),
                (5, false)
            ],
            corners: [0; 4],
        }
    }
}
impl State {
    pub fn pack(self) -> u32 {
        // edges first; each edge is numberd 0..=5 and a bool
        let edges = self.edges.iter().copied().map(|(n,f)| (((f as u32) << 3) | n as u32))
            .fold(0, |acc, new| acc << 4 | new);
        let corners = self.corners.iter().map(|c| *c as u32 % 3).fold(edges, |a,n| a << 2 | n);
        corners
    }

    pub fn unpack(mut v: u32) -> Self {
        let mut res = Self::default();
        for i in 0..6 {
            let slot = v >> 28;
            let flip = slot & 8 != 0;
            let n = (slot & 7) as u8;
            res.edges[i] = (n, flip);
            v <<= 4;
        }
        for i in 0..4 {
            res.corners[i] = ((v >> 30) & 3) as u8;
            v <<= 2;
        }
        res
    }

    const fn mk_move(corner: usize, dir: bool) -> Self {
        let mut state = Self {
            edges: [
                (0, false),
                (1, false),
                (2, false),
                (3, false),
                (4, false),
                (5, false)
            ],
            corners: [0; 4],
        }
            ;
        let mut edges = match corner {
            0 => [4,5,3],
            1 => [0,1,3],
            2 => [2,4,1],
            3 => [2,0,5],
            _ => unimplemented!()
        };

        if !dir {
            // counter-clockwise
            let e0 = edges[1];
            edges[1] = edges[2];
            edges[2] = e0;
        }

        const fn mflip((n,f): (u8, bool), df: bool) -> (u8, bool) {
            (n, f ^ df)
        }

        state.edges[edges[1]] = (edges[0] as u8, true);
        state.edges[edges[2]] = (edges[1] as u8, false);
        state.edges[edges[0]] = (edges[2] as u8, true);

        state.corners[corner] = if dir {
            1
        } else {
            2
        };

        state
    }
}

impl Display for State {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        let mut res = String::with_capacity(11);
        for (n,flip) in self.edges {
            res.push(char::from(if flip { b'A'} else { b'a'} + n) );
        }
        res.push('/');
        for d in self.corners {
            res.push(match d {
                0 => ',',
                1 => '+',
                2 => '-',
                _ => '?',
            })
        }
        f.write_str(res.as_str())
    }
}

impl From<u32> for State {
    fn from(value: u32) -> Self {
        State::unpack(value)
    }
}

impl From<State> for u32 {
    fn from(value: State) -> Self {
        value.pack()
    }
}

impl Add for State {
    type Output = State;

    fn add(self, rhs: Self) -> Self::Output {
        let mut result = self;
        for i in 0..6 {
            let (sn, sf) = rhs.edges[i];
            let (rn, rf) = self.edges[sn as usize];
            result.edges[i] = (rn, rf ^ sf);
        }
        for i in 0..4 {
            result.corners[i] = (self.corners[i] + rhs.corners[i]) % 3; 
        }
        result
    }
}

pub const M0P: State = State::mk_move(0, true);
pub const M1P: State = State::mk_move(1, true);
pub const M2P: State = State::mk_move(2, true);
pub const M3P: State = State::mk_move(3, true);

pub const M0N: State = State::mk_move(0, false);
pub const M1N: State = State::mk_move(1, false);
pub const M2N: State = State::mk_move(2, false);
pub const M3N: State = State::mk_move(3, false);

#[cfg(test)]
mod test {
    use super::*;
    fn test_flipped(s: State, edge: usize) -> bool {
        s.edges[edge] == (edge as u8, true)
    }

    macro_rules! test_flipped {
        ($mov:expr, $edge:expr) => {{
            let mov = $mov;
            assert_eq!(mov.edges[$edge], ($edge, true));
        }}
    }

    #[test]
    fn test_203_2() {
        test_flipped!(M2P + M0P + M3P, 2)
    }

    #[test]
    fn test_312_2() {
        test_flipped!(M3P + M1P + M2P, 2)
    }
    #[test]
    fn test_102_1() {
        test_flipped!(M1P + M0P + M2P, 1)
    }
    #[test]
    fn test_231_1() {
        test_flipped!(M2P + M3P + M1P, 1)
    }
    #[test]
    fn test_301_0() {
        test_flipped!(M3P + M0P + M1P, 0)
    }
    #[test]
    fn test_123_0() {
        test_flipped!(M1P + M2P + M3P, 0)
    }


    #[test]
    fn test_210_4() {
        test_flipped!(M2P + M1P + M0P, 4)
    }
    #[test]
    fn test_032_4() {
        test_flipped!(M0P + M3P + M2P, 4)
    }
    #[test]
    fn test_130_3() {
        test_flipped!(M1P+M3P+M0P, 3)
    }
    #[test]
    fn test_021_3() {
        test_flipped!(M0P+M2P+M1P, 3)
    }
    #[test]
    fn test_320_5() {
        test_flipped!(M2P + M0P + M3P, 2)
    }
    #[test]
    fn test_013_5() {
        test_flipped!(M0P+M1P+M3P, 5)
    }

    #[test]
    fn test_pack() {
        let st = State::default();
        assert_eq!(st, State::unpack(st.into()))
    }
}