chess/

square.rs

use std::cmp::max;
use std::fmt;
use std::str::FromStr;

use crate::{
    Color, Direction, Error, File, Rank, BOARD_CELL_PX_SIZE, BOARD_SIZE, NUM_FILES, NUM_RANKS,
};

/// Represent a square on the chess board.
#[rustfmt::skip]
#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug)]
#[repr(u8)]
pub enum Square {
    A1, B1, C1, D1, E1, F1, G1, H1,
    A2, B2, C2, D2, E2, F2, G2, H2,
    A3, B3, C3, D3, E3, F3, G3, H3,
    A4, B4, C4, D4, E4, F4, G4, H4,
    A5, B5, C5, D5, E5, F5, G5, H5,
    A6, B6, C6, D6, E6, F6, G6, H6,
    A7, B7, C7, D7, E7, F7, G7, H7,
    A8, B8, C8, D8, E8, F8, G8, H8,
}

/// Numbers of [`Square`].
pub const NUM_SQUARES: usize = (BOARD_SIZE.0 * BOARD_SIZE.1) as usize;

/// Enumerate all [`Square`].
#[rustfmt::skip]
pub const ALL_SQUARES: [Square; NUM_SQUARES] = [
    Square::A1, Square::B1, Square::C1, Square::D1, Square::E1, Square::F1, Square::G1, Square::H1,
    Square::A2, Square::B2, Square::C2, Square::D2, Square::E2, Square::F2, Square::G2, Square::H2,
    Square::A3, Square::B3, Square::C3, Square::D3, Square::E3, Square::F3, Square::G3, Square::H3,
    Square::A4, Square::B4, Square::C4, Square::D4, Square::E4, Square::F4, Square::G4, Square::H4,
    Square::A5, Square::B5, Square::C5, Square::D5, Square::E5, Square::F5, Square::G5, Square::H5,
    Square::A6, Square::B6, Square::C6, Square::D6, Square::E6, Square::F6, Square::G6, Square::H6,
    Square::A7, Square::B7, Square::C7, Square::D7, Square::E7, Square::F7, Square::G7, Square::H7,
    Square::A8, Square::B8, Square::C8, Square::D8, Square::E8, Square::F8, Square::G8, Square::H8,
];

impl Square {
    /// Create a new [`Square`], from an index.
    ///
    /// # Panics
    ///
    /// Panic if the index is not in the range 0..=63.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::Square;
    ///
    /// assert_eq!(Square::new(0), Square::A1);
    /// assert_eq!(Square::new(63), Square::H8);
    /// ```
    #[inline]
    pub fn new(index: usize) -> Self {
        ALL_SQUARES[index]
    }

    /// Convert this [`Square`] into a [`usize`].
    #[inline]
    pub fn to_index(&self) -> usize {
        *self as usize
    }

    /// Make a square from [`File`] and [`Rank`].
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{File, Rank, Square};
    ///
    /// // Make the A1 square
    /// let square = Square::make_square(File::A, Rank::First);
    /// ```
    #[inline]
    pub fn make_square(file: File, rank: Rank) -> Square {
        Square::new(file.to_index() + rank.to_index() * BOARD_SIZE.0 as usize)
    }

    /// Transform a screen coordinate into a [`Square`].
    ///
    /// > **Reciprocal**: see [`Square::to_screen`].
    ///
    /// The result depend of:
    /// - [`BOARD_SIZE`]
    /// - [`BOARD_CELL_PX_SIZE`]
    #[inline]
    pub fn from_screen(x: f32, y: f32) -> Square {
        // Transpose to grid space
        let x = x / BOARD_CELL_PX_SIZE.0;
        let y = y / BOARD_CELL_PX_SIZE.1;

        // transpose to Square (return the y-axis)
        let y = BOARD_SIZE.1 - y as i16 - 1;
        Square::make_square(File::new(x as usize), Rank::new(y as usize))
    }

    /// Transform a [`Square`] into a screen coordinate.
    ///
    /// > **Reciprocal**: see [`Square::from_screen`].
    ///
    /// The result depend of:
    /// - [`BOARD_SIZE`]
    /// - [`BOARD_CELL_PX_SIZE`]
    #[inline]
    pub fn to_screen(&self) -> (f32, f32) {
        // transpose to grid space (return the y-axis)
        let x = self.file().to_index() as f32;
        let y = (BOARD_SIZE.1 as usize - self.rank().to_index() - 1) as f32;

        // Transpose to screen space
        let x = x * BOARD_CELL_PX_SIZE.0;
        let y = y * BOARD_CELL_PX_SIZE.1;
        (x, y)
    }

    /// Return the [`File`] of this square.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{File, Rank, Square};
    ///
    /// let square = Square::make_square(File::D, Rank::Seventh);
    ///
    /// assert_eq!(square.file(), File::D);
    /// ```
    #[inline]
    pub fn file(&self) -> File {
        File::new(self.to_index() % NUM_FILES)
    }

    /// Return the "relative" [`File`] of this square according the side.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, File, Square};
    ///
    /// assert_eq!(Square::A1.file_for(Color::White), File::A);
    /// assert_eq!(Square::A1.file_for(Color::Black), File::H);
    /// ```
    #[inline]
    pub fn file_for(&self, color: Color) -> File {
        let file = self.file();
        match color {
            Color::White => file,
            Color::Black => File::new(NUM_FILES - file.to_index() - 1),
        }
    }

    /// Return the [`Rank`] of this square.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{File, Rank, Square};
    ///
    /// let square = Square::make_square(File::D, Rank::Seventh);
    ///
    /// assert_eq!(square.rank(), Rank::Seventh);
    /// ```
    #[inline]
    pub fn rank(&self) -> Rank {
        Rank::new(self.to_index() / NUM_RANKS)
    }

    /// Return the "relative" [`Rank`] of this square according the side.
    /// (i.e. return ranks for black)
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Rank, Square};
    ///
    /// assert_eq!(Square::E1.rank_for(Color::White), Rank::First);
    /// assert_eq!(Square::E8.rank_for(Color::White), Rank::Eighth);
    /// assert_eq!(Square::E2.rank_for(Color::Black), Rank::Seventh);
    /// assert_eq!(Square::E7.rank_for(Color::Black), Rank::Second);
    /// ```
    #[inline]
    pub fn rank_for(&self, color: Color) -> Rank {
        let rank = self.rank();
        match color {
            Color::White => rank,
            Color::Black => Rank::new(NUM_RANKS - rank.to_index() - 1),
        }
    }

    /// Go one [`Rank`] up.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::Square;
    ///
    /// assert_eq!(Square::B2.up(), Square::B3);
    /// ```
    #[inline]
    pub fn up(&self) -> Self {
        Square::make_square(self.file(), self.rank().up())
    }

    /// Go *n* [`Rank`] up.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::Square;
    ///
    /// assert_eq!(Square::B2.n_up(3), Square::B5);
    /// ```
    #[inline]
    pub fn n_up(&self, n: usize) -> Self {
        let mut square = *self;
        for _ in 0..n {
            square = square.up();
        }
        square
    }

    /// Go one [`Rank`] forward according to the side.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Square};
    ///
    /// assert_eq!(Square::B2.forward(Color::White), Square::B3);
    /// assert_eq!(Square::B2.forward(Color::Black), Square::B1);
    /// ```
    #[inline]
    pub fn forward(&self, color: Color) -> Self {
        match color {
            Color::White => Square::make_square(self.file(), self.rank().up()),
            Color::Black => Square::make_square(self.file(), self.rank().down()),
        }
    }

    /// Go *n* [`Rank`] forward according to the side.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Square};
    ///
    /// assert_eq!(Square::B2.n_forward(Color::White, 2), Square::B4);
    /// assert_eq!(Square::B8.n_forward(Color::Black, 5), Square::B3);
    /// ```
    #[inline]
    pub fn n_forward(&self, color: Color, n: usize) -> Self {
        let mut square = *self;
        for _ in 0..n {
            square = square.forward(color);
        }
        square
    }

    /// Go one [`Rank`] down.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::Square;
    ///
    /// assert_eq!(Square::B2.down(), Square::B1);
    /// ```
    #[inline]
    pub fn down(&self) -> Self {
        Square::make_square(self.file(), self.rank().down())
    }

    /// Go *n* [`Rank`] down.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Square};
    ///
    /// assert_eq!(Square::B4.n_down(2), Square::B2);
    /// ```
    #[inline]
    pub fn n_down(&self, n: usize) -> Self {
        let mut square = *self;
        for _ in 0..n {
            square = square.down();
        }
        square
    }

    /// Go one [`Rank`] backward according to the side.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Square};
    ///
    /// assert_eq!(Square::B2.backward(Color::White), Square::B1);
    /// assert_eq!(Square::B2.backward(Color::Black), Square::B3);
    /// ```
    #[inline]
    pub fn backward(&self, color: Color) -> Self {
        match color {
            Color::White => Square::make_square(self.file(), self.rank().down()),
            Color::Black => Square::make_square(self.file(), self.rank().up()),
        }
    }

    /// Go *n* [`Rank`] backward according to the side.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Square};
    ///
    /// assert_eq!(Square::B4.n_backward(Color::White, 2), Square::B2);
    /// assert_eq!(Square::B3.n_backward(Color::Black, 5), Square::B8);
    /// ```
    #[inline]
    pub fn n_backward(&self, color: Color, n: usize) -> Self {
        let mut square = *self;
        for _ in 0..n {
            square = square.backward(color);
        }
        square
    }

    /// Go one [`File`] to the right.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::Square;
    ///
    /// assert_eq!(Square::B2.right(), Square::C2);
    /// ```
    #[inline]
    pub fn right(&self) -> Self {
        Square::make_square(self.file().right(), self.rank())
    }

    /// Go *n* [`File`] to the right.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Square};
    ///
    /// assert_eq!(Square::A4.n_right(3), Square::D4);
    /// ```
    #[inline]
    pub fn n_right(&self, n: usize) -> Self {
        let mut square = *self;
        for _ in 0..n {
            square = square.right();
        }
        square
    }

    /// Go one [`File`] right according to the side.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Square};
    ///
    /// assert_eq!(Square::B2.right_for(Color::White), Square::C2);
    /// assert_eq!(Square::B2.right_for(Color::Black), Square::A2);
    /// ```
    #[inline]
    pub fn right_for(&self, color: Color) -> Self {
        match color {
            Color::White => Square::make_square(self.file().right(), self.rank()),
            Color::Black => Square::make_square(self.file().left(), self.rank()),
        }
    }

    /// Go *n* [`File`] to the right according to the side.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Square};
    ///
    /// assert_eq!(Square::A4.n_right_for(Color::White, 3), Square::D4);
    /// assert_eq!(Square::D4.n_right_for(Color::Black, 3), Square::A4);
    /// ```
    #[inline]
    pub fn n_right_for(&self, color: Color, n: usize) -> Self {
        let mut square = *self;
        for _ in 0..n {
            square = square.right_for(color);
        }
        square
    }

    /// Go one [`File`] to the left.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::Square;
    ///
    /// assert_eq!(Square::B2.left(), Square::A2);
    /// ```
    #[inline]
    pub fn left(&self) -> Self {
        Square::make_square(self.file().left(), self.rank())
    }

    /// Go *n* [`File`] to the left.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Square};
    ///
    /// assert_eq!(Square::D4.n_left(3), Square::A4);
    /// ```
    #[inline]
    pub fn n_left(&self, n: usize) -> Self {
        let mut square = *self;
        for _ in 0..n {
            square = square.left();
        }
        square
    }

    /// Go one [`File`] left according to the side.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Square};
    ///
    /// assert_eq!(Square::B2.left_for(Color::White), Square::A2);
    /// assert_eq!(Square::B2.left_for(Color::Black), Square::C2);
    /// ```
    #[inline]
    pub fn left_for(&self, color: Color) -> Self {
        match color {
            Color::White => Square::make_square(self.file().left(), self.rank()),
            Color::Black => Square::make_square(self.file().right(), self.rank()),
        }
    }

    /// Go *n* [`File`] to the left according to the side.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Color, Square};
    ///
    /// assert_eq!(Square::D4.n_left_for(Color::White, 3), Square::A4);
    /// assert_eq!(Square::A4.n_left_for(Color::Black, 3), Square::D4);
    /// ```
    #[inline]
    pub fn n_left_for(&self, color: Color, n: usize) -> Self {
        let mut square = *self;
        for _ in 0..n {
            square = square.left_for(color);
        }
        square
    }

    /// Go one [`Square`] in the given direction.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::{Direction, Square};
    ///
    /// assert_eq!(Square::B2.follow_direction(Direction::Up), Square::B3);
    /// assert_eq!(Square::B2.follow_direction(Direction::DownRight), Square::C1);
    /// ```
    #[inline]
    pub fn follow_direction(&self, direction: Direction) -> Self {
        match direction {
            Direction::Up => self.up(),
            Direction::UpRight => self.up().right(),
            Direction::Right => self.right(),
            Direction::DownRight => self.down().right(),
            Direction::Down => self.down(),
            Direction::DownLeft => self.down().left(),
            Direction::Left => self.left(),
            Direction::UpLeft => self.up().left(),
        }
    }

    /// The distance between the two squares, i.e. the number of king steps
    /// to get from one square to the other.
    ///
    /// # Examples
    ///
    /// ```
    /// use chess::Square;
    ///
    /// assert_eq!(Square::A2.distance(Square::B5), 3);
    /// ```
    pub fn distance(&self, other: Square) -> u32 {
        max(
            self.file().distance(other.file()),
            self.rank().distance(other.rank()),
        )
    }
}

impl fmt::Display for Square {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(
            f,
            "{}{}",
            (b'a' + (self.file() as u8)) as char,
            (b'1' + (self.rank() as u8)) as char
        )
    }
}

impl FromStr for Square {
    type Err = Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if s.len() < 2 {
            return Err(Error::InvalidSquare);
        }
        let ch: Vec<char> = s.chars().collect();
        match ch[0] {
            'a' | 'b' | 'c' | 'd' | 'e' | 'f' | 'g' | 'h' => {}
            _ => return Err(Error::InvalidSquare),
        }
        match ch[1] {
            '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' => {}
            _ => return Err(Error::InvalidSquare),
        }
        Ok(Square::make_square(
            File::new((ch[0] as usize) - ('a' as usize)),
            Rank::new((ch[1] as usize) - ('1' as usize)),
        ))
    }
}

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

    #[test]
    fn test_square() {
        for file in (0..8).map(File::new) {
            for rank in (0..8).map(Rank::new) {
                let square = Square::make_square(file, rank);
                assert_eq!(square.file(), file);
                assert_eq!(square.rank(), rank);
            }
        }
    }
}