// Eryn Wells <eryn@erynwells.me>

use chessfriend_core::{Rank, Square};

/// En passant information.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct EnPassant {
    target: Square,
    capture: Square,
}

impl EnPassant {
    fn _capture_square(target: Square) -> Option<Square> {
        let (file, rank) = target.file_rank();
        match rank {
            Rank::THREE => Some(Square::from_file_rank(file, Rank::FOUR)),
            Rank::SIX => Some(Square::from_file_rank(file, Rank::FIVE)),
            _ => None,
        }
    }

    /// Return en passant information for a particular target square. The target
    /// square is the square a pawn capturing en passant will move to.
    ///
    /// Return `None` if the square is not eligible for en passant.
    ///
    /// ## Examples
    ///
    /// ```
    /// use chessfriend_board::en_passant::EnPassant;
    /// use chessfriend_core::Square;
    /// assert!(EnPassant::from_target_square(Square::E3).is_some());
    /// assert!(EnPassant::from_target_square(Square::B4).is_none());
    /// ```
    pub fn from_target_square(target: Square) -> Option<Self> {
        Self::_capture_square(target).map(|capture| Self { target, capture })
    }

    /// The square the capturing piece will move to.
    pub fn target_square(self) -> Square {
        self.target
    }

    /// The square on which the captured pawn sits.
    pub fn capture_square(self) -> Square {
        self.capture
    }
}