// Eryn Wells <eryn@erynwells.me>

mod captures;

use crate::fen::{FromFenStr, FromFenStrError};
use captures::CapturesList;
use chessfriend_bitboard::BitBoard;
use chessfriend_board::{
    display::DiagramFormatter, fen::ToFenStr, Board, PlacePieceError, PlacePieceStrategy,
    ZobristState,
};
use chessfriend_core::{Color, Piece, Shape, Square};
use chessfriend_moves::{
    algebraic::AlgebraicMoveComponents,
    generators::{
        AllPiecesMoveGenerator, BishopMoveGenerator, KingMoveGenerator, KnightMoveGenerator,
        PawnMoveGenerator, QueenMoveGenerator, RookMoveGenerator,
    },
    GeneratedMove, MakeMove, MakeMoveError, Move, MoveRecord, UnmakeMove, UnmakeMoveError,
    UnmakeMoveResult, ValidateMove,
};
use std::{collections::HashSet, fmt, sync::Arc};

#[must_use]
#[derive(Clone, Debug, Default, Eq)]
pub struct Position {
    pub board: Board,
    pub(crate) moves: Vec<MoveRecord>,
    pub(crate) captures: CapturesList,

    /// A set of hashes of board positions seen throughout the move record.
    boards_seen: HashSet<u64>,
}

impl Position {
    pub fn empty(zobrist: Option<Arc<ZobristState>>) -> Self {
        Self::new(Board::empty(zobrist))
    }

    /// Return a starting position.
    pub fn starting(zobrist: Option<Arc<ZobristState>>) -> Self {
        Self::new(Board::starting(zobrist))
    }

    pub fn new(board: Board) -> Self {
        Self {
            board,
            ..Default::default()
        }
    }
}

impl Position {
    /// Place a piece on the board.
    ///
    /// ## Errors
    ///
    /// See [`chessfriend_board::Board::place_piece`].
    pub fn place_piece(
        &mut self,
        piece: Piece,
        square: Square,
        strategy: PlacePieceStrategy,
    ) -> Result<Option<Piece>, PlacePieceError> {
        self.board.place_piece(piece, square, strategy)
    }

    #[must_use]
    pub fn get_piece(&self, square: Square) -> Option<Piece> {
        self.board.get_piece(square)
    }

    pub fn remove_piece(&mut self, square: Square) -> Option<Piece> {
        self.board.remove_piece(square)
    }
}

impl Position {
    pub fn sight(&self, square: Square) -> BitBoard {
        self.board.sight(square)
    }

    pub fn movement(&self, square: Square) -> BitBoard {
        self.board.movement(square)
    }
}

impl Position {
    pub fn all_moves(&self, color: Option<Color>) -> AllPiecesMoveGenerator {
        AllPiecesMoveGenerator::new(&self.board, color)
    }

    /// Generate legal moves.
    ///
    /// ## Panics
    ///
    /// If the position failed to make a move generated by the internal move
    /// generator, this method will panic.
    #[must_use]
    pub fn all_legal_moves(
        &self,
        color: Option<Color>,
    ) -> Box<dyn Iterator<Item = GeneratedMove> + '_> {
        let generator = self.all_moves(color);

        let mut test_board = self.board.clone();
        Box::new(generator.filter(move |ply| {
            let active_color_before_move = test_board.active_color();

            let ply: Move = ply.clone().into();
            let record = test_board
                .make_move(ply, ValidateMove::No)
                .unwrap_or_else(|err| {
                    panic!(
                        "unable to make generated move [{ply}]: {err}\n\n{}",
                        test_board.display().highlight(ply.relevant_squares())
                    );
                });

            let move_is_legal = !test_board.color_is_in_check(Some(active_color_before_move));

            test_board.unmake_move(&record).unwrap_or_else(|err| {
                panic!(
                    "unable to unmake generated move [{ply}]: {err}\n\n{}",
                    test_board.display().highlight(ply.relevant_squares())
                );
            });

            move_is_legal
        }))
    }

    #[must_use]
    pub fn moves_for_piece(
        &self,
        square: Square,
    ) -> Option<Box<dyn Iterator<Item = GeneratedMove>>> {
        self.get_piece(square)
            .map(|piece| Self::generator(&self.board, piece))
    }

    #[must_use]
    fn generator(board: &Board, piece: Piece) -> Box<dyn Iterator<Item = GeneratedMove>> {
        match piece.shape {
            Shape::Pawn => Box::new(PawnMoveGenerator::new(board, Some(piece.color))),
            Shape::Knight => Box::new(KnightMoveGenerator::new(board, Some(piece.color))),
            Shape::Bishop => Box::new(BishopMoveGenerator::new(board, Some(piece.color))),
            Shape::Rook => Box::new(RookMoveGenerator::new(board, Some(piece.color))),
            Shape::Queen => Box::new(QueenMoveGenerator::new(board, Some(piece.color))),
            Shape::King => Box::new(KingMoveGenerator::new(board, Some(piece.color))),
        }
    }
}

impl Position {
    pub fn active_sight(&self) -> BitBoard {
        self.board.active_sight()
    }

    /// A [`BitBoard`] of all squares the given color can see.
    pub fn friendly_sight(&self, color: Color) -> BitBoard {
        self.board.friendly_sight(color)
    }

    /// A [`BitBoard`] of all squares visible by colors that oppose the given color.
    pub fn active_color_opposing_sight(&self) -> BitBoard {
        self.board.active_color_opposing_sight()
    }
}

impl Position {
    /// Make a move on the board and record it in the move list. Returns `true`
    /// if the board position has been seen before (i.e. it's a repetition).
    ///
    /// ## Errors
    ///
    /// Returns one of [`MakeMoveError`] if the move cannot be made.
    ///
    pub fn make_move(&mut self, ply: Move, validate: ValidateMove) -> Result<bool, MakeMoveError> {
        let record = self.board.make_move(ply, validate)?;

        if let Some(captured_piece) = record.captured_piece {
            self.captures.push(record.color, captured_piece);
        }

        let has_seen = if let Some(hash) = self.board.zobrist_hash() {
            // HashSet::insert() returns true if the value does not exist in the
            // set when it's called.
            !self.boards_seen.insert(hash)
        } else {
            false
        };

        self.moves.push(record.clone());

        Ok(has_seen)
    }

    /// Unmake the last move made on the board and remove its record from the
    /// move list.
    ///
    /// ## Errors
    ///
    /// Returns one of [`UnmakeMoveError`] if the move cannot be made.
    ///
    pub fn unmake_last_move(&mut self) -> UnmakeMoveResult {
        let last_move_record = self.moves.pop().ok_or(UnmakeMoveError::NoMove)?;

        let hash_before_unmake = self.board.zobrist_hash();

        let unmake_result = self.board.unmake_move(&last_move_record);

        if unmake_result.is_ok() {
            if let Some(capture) = last_move_record.captured_piece {
                let popped_piece = self.captures.pop(last_move_record.color);
                debug_assert_eq!(Some(capture), popped_piece);
            }

            if let Some(hash_before_unmake) = hash_before_unmake {
                self.boards_seen.remove(&hash_before_unmake);
            }
        } else {
            self.moves.push(last_move_record);
        }

        unmake_result
    }

    /// Build a move given its origin, target, and possible promotion. Perform
    /// some minimal validation. If a move cannot be
    #[must_use]
    pub fn move_from_algebraic_components(
        &self,
        components: AlgebraicMoveComponents,
    ) -> Option<Move> {
        match components {
            AlgebraicMoveComponents::Null => Some(Move::null()),
            AlgebraicMoveComponents::Regular {
                origin,
                target,
                promotion,
            } => self.move_from_origin_target(origin, target, promotion),
        }
    }

    fn move_from_origin_target(
        &self,
        origin: Square,
        target: Square,
        promotion: Option<Shape>,
    ) -> Option<Move> {
        let piece = self.get_piece(origin)?;

        let color = piece.color;

        // Pawn and King are the two most interesting shapes here, because of en
        // passant, castling and so on. So, let the move generators do their
        // thing and find the move that fits the parameters. For the rest of the
        // pieces, do something a little more streamlined.

        match piece.shape {
            Shape::Pawn => PawnMoveGenerator::new(&self.board, None)
                .find(|ply| {
                    ply.origin() == origin
                        && ply.target() == target
                        && ply.promotion_shape() == promotion
                })
                .map(std::convert::Into::into),
            Shape::King => KingMoveGenerator::new(&self.board, None)
                .find(|ply| ply.origin() == origin && ply.target() == target)
                .map(std::convert::Into::into),
            _ => {
                if color != self.board.active_color() {
                    return None;
                }

                let target_bitboard: BitBoard = target.into();
                if !(self.movement(origin) & target_bitboard).is_populated() {
                    return None;
                }

                if self.get_piece(target).is_some() {
                    return Some(Move::capture(origin, target));
                }

                Some(Move::quiet(origin, target))
            }
        }
    }
}

impl Position {
    #[must_use]
    pub fn zobrist_hash(&self) -> Option<u64> {
        self.board.zobrist_hash()
    }

    pub fn set_zobrist_state(&mut self, state: Arc<ZobristState>) {
        self.board.set_zobrist_state(state);
    }
}

impl Position {
    pub fn display(&self) -> DiagramFormatter {
        self.board.display()
    }
}

impl FromFenStr for Position {
    type Error = FromFenStrError;

    fn from_fen_str(string: &str) -> Result<Self, Self::Error> {
        let board = Board::from_fen_str(string)?;
        Ok(Position::new(board))
    }
}

impl ToFenStr for Position {
    type Error = <Board as ToFenStr>::Error;

    fn to_fen_str(&self) -> Result<String, Self::Error> {
        self.board.to_fen_str()
    }
}

impl PartialEq for Position {
    fn eq(&self, other: &Self) -> bool {
        self.board == other.board
    }
}

impl fmt::Display for Position {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.board.display())?;

        if !self.captures.is_empty() {
            write!(f, "\n\n{}", self.captures)?;
        }

        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{test_position, Position};
    use chessfriend_core::piece;

    #[test]
    fn piece_on_square() {
        let pos = test_position![
            Black Bishop on F7,
        ];

        let piece = pos.board.get_piece(Square::F7);
        assert_eq!(piece, Some(piece!(Black Bishop)));
    }

    #[test]
    fn piece_in_starting_position() {
        let pos = test_position!(starting);

        assert_eq!(pos.board.get_piece(Square::H1), Some(piece!(White Rook)));
        assert_eq!(pos.board.get_piece(Square::A8), Some(piece!(Black Rook)));
    }
}