/// A singular type for all errors that could happen during [crate::board::ChessBoard::is_valid].
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum ValidationError {
    /// Too many pieces.
    TooManyPieces,
    /// Missing king.
    MissingKing,
    /// Pawns on the first/last rank.
    InvalidPawnPosition,
    /// Castling rights do not match up with the state of the board.
    InvalidCastlingRights,
    /// En-passant target square is not empty, behind an opponent's pawn, on the correct rank.
    InvalidEnPassant,
    /// The two kings are next to each other.
    NeighbouringKings,
    /// The opponent is currently in check.
    OpponentInCheck,
    /// The piece-specific boards are overlapping.
    OverlappingPieces,
    /// The color-specific boards are overlapping.
    OverlappingColors,
    /// The pre-computed combined occupancy boards does not match the other boards.
    ErroneousCombinedOccupancy,
    /// Half-move clock is higher than total number of plies.
    HalfMoveClockTooHigh,
    /// The total plie count does not match the current player.
    IncoherentPlieCount,
}

impl std::fmt::Display for ValidationError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let error_msg = match self {
            Self::TooManyPieces => "too many pieces",
            Self::MissingKing => "missing king",
            Self::InvalidPawnPosition => "pawns on the first/last rank",
            Self::InvalidCastlingRights => {
                "castling rights do not match up with the state of the board"
            }
            Self::InvalidEnPassant => {
                "en-passant target square is not empty, behind an opponent's pawn, on the correct rank"
            }
            Self::NeighbouringKings => "the two kings are next to each other",
            Self::OpponentInCheck => "the opponent is currently in check",
            Self::OverlappingPieces => "the piece-specific boards are overlapping",
            Self::OverlappingColors => "the color-specific boards are overlapping",
            Self::ErroneousCombinedOccupancy => {
                "the pre-computed combined occupancy boards does not match the other boards"
            }
            Self::HalfMoveClockTooHigh => "half-move clock is higher than total number of plies",
            Self::IncoherentPlieCount => "the total plie count does not match the current player",
        };
        write!(f, "{}", error_msg)
    }
}

impl std::error::Error for ValidationError {}