chessfriend/moves/src/moves.rs

// Eryn Wells <eryn@erynwells.me>

use crate::builder::Builder;
use crate::defs::Kind;
use chessfriend_core::{Rank, Shape, Square, Wing};
use std::fmt;

/// A single player's move. In game theory parlance, this is a "ply".
///
/// ## TODO
///
/// - Rename this class `Ply`.
///
#[derive(Clone, Copy, Eq, Hash, PartialEq)]
pub struct Move(pub(crate) u16);

impl Move {
    #[must_use]
    #[allow(clippy::missing_panics_doc)]
    pub fn origin_square(&self) -> Square {
        ((self.0 >> 4) & 0b111_111).try_into().unwrap()
    }

    #[must_use]
    #[allow(clippy::missing_panics_doc)]
    pub fn target_square(&self) -> Square {
        (self.0 >> 10).try_into().unwrap()
    }

    #[must_use]
    pub fn capture_square(&self) -> Option<Square> {
        if self.is_en_passant() {
            let target_square = self.target_square();
            return Some(match target_square.rank() {
                Rank::THREE => Square::from_file_rank(target_square.file(), Rank::FOUR),
                Rank::SIX => Square::from_file_rank(target_square.file(), Rank::FIVE),
                _ => unreachable!(),
            });
        }

        if self.is_capture() {
            return Some(self.target_square());
        }

        None
    }

    #[must_use]
    pub fn is_quiet(&self) -> bool {
        self.flags() == Kind::Quiet as u16
    }

    #[must_use]
    pub fn is_double_push(&self) -> bool {
        self.flags() == Kind::DoublePush as u16
    }

    #[must_use]
    pub fn is_castle(&self) -> bool {
        (self.0 & 0b0010) != 0
    }

    #[must_use]
    pub fn castle(&self) -> Option<Wing> {
        match self.flags() {
            0b0010 => Some(Wing::KingSide),
            0b0011 => Some(Wing::QueenSide),
            _ => None,
        }
    }

    #[must_use]
    pub fn is_capture(&self) -> bool {
        (self.0 & Kind::Capture as u16) != 0
    }

    #[must_use]
    pub fn is_en_passant(&self) -> bool {
        self.flags() == Kind::EnPassantCapture as u16
    }

    #[must_use]
    pub fn is_promotion(&self) -> bool {
        (self.0 & Kind::Promotion as u16) != 0
    }

    #[must_use]
    pub fn promotion(&self) -> Option<Shape> {
        if !self.is_promotion() {
            return None;
        }

        Some(match self.special() {
            0b00 => Shape::Knight,
            0b01 => Shape::Bishop,
            0b10 => Shape::Rook,
            0b11 => Shape::Queen,
            _ => unreachable!(),
        })
    }
}

impl Move {
    #[inline]
    fn flags(self) -> u16 {
        self.0 & 0b1111
    }

    #[inline]
    fn special(self) -> u16 {
        self.0 & 0b11
    }
}

impl Move {
    fn transfer_char(self) -> char {
        if self.is_capture() || self.is_en_passant() {
            'x'
        } else {
            '-'
        }
    }
}

const KINGSIDE_CASTLE_STR: &str = "0-0";
const QUEENSIDE_CASTLE_STR: &str = "0-0-0";

impl fmt::Display for Move {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if let Some(castle) = self.castle() {
            return match castle {
                Wing::KingSide => write!(f, "{KINGSIDE_CASTLE_STR}"),
                Wing::QueenSide => write!(f, "{QUEENSIDE_CASTLE_STR}"),
            };
        }

        let origin = self.origin_square();
        let target = self.target_square();
        let transfer_char = self.transfer_char();
        write!(f, "{origin}{transfer_char}{target}")?;

        if let Some(promotion) = self.promotion() {
            write!(f, "={promotion}")?;
        } else if self.is_en_passant() {
            write!(f, " e.p.")?;
        }

        Ok(())
    }
}

impl fmt::Debug for Move {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("Move")
            .field(&format_args!("{:08b}", &self.0))
            .finish()
    }
}