// Eryn Wells <eryn@erynwells.me>

use std::io::empty;

use crate::{
    bitboard::BitBoard,
    piece::{Color, Piece},
    Move, Position,
};

enum MoveList {
    Quiet,
    Captures,
}

pub(super) struct KnightMoveGenerator<'pos> {
    position: &'pos Position,
    color: Color,

    bitboards: [BitBoard; 2],
    move_lists: [Vec<Move>; 2],
}

impl<'pos> KnightMoveGenerator<'pos> {
    pub(super) fn new(position: &'pos Position, color: Color) -> KnightMoveGenerator<'pos> {
        let mut generator = KnightMoveGenerator {
            position,
            color,
            bitboards: [BitBoard::empty(), BitBoard::empty()],
            move_lists: [Vec::new(), Vec::new()],
        };

        generator.generate_moves();

        generator
    }

    pub(super) fn iter(&self) -> impl Iterator<Item = &Move> + '_ {
        self.move_lists.iter().flatten()
    }

    fn quiet_moves_list_mut(&mut self) -> &mut Vec<Move> {
        &mut self.move_lists[MoveList::Quiet as usize]
    }

    fn capture_moves_list_mut(&mut self) -> &mut Vec<Move> {
        &mut self.move_lists[MoveList::Captures as usize]
    }

    fn generate_moves(&mut self) {
        self.generate_bitboards();
        self.populate_move_lists();
    }

    fn generate_bitboards(&mut self) {
        // TODO: Calculate bitboards for each knight.
    }

    fn populate_move_lists(&mut self) {
        let piece = Piece::knight(self.color);

        let bb = self.position.bitboard_for_piece(piece);
        if bb.is_empty() {
            return;
        }

        let empty_squares = self.position.empty_squares();
        let opposing_pieces = self.position.bitboard_for_color(self.color.other());

        for from_sq in bb.occupied_squares() {
            let knight_moves = BitBoard::knight_moves(from_sq);
            println!("{}", knight_moves);

            let new_moves = (knight_moves & empty_squares)
                .occupied_squares()
                .map(|to_sq| Move::new(piece, from_sq, to_sq));
            self.quiet_moves_list_mut().extend(new_moves);

            let new_capture_moves =
                (knight_moves & opposing_pieces)
                    .occupied_squares()
                    .map(|to_sq| {
                        let captured_piece = self.position.piece_on_square(to_sq).unwrap();
                        Move::new(piece, from_sq, to_sq).capturing(captured_piece)
                    });
            self.capture_moves_list_mut().extend(new_capture_moves);
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::Square;
    use std::collections::HashSet;

    #[test]
    fn one_knight() {
        let mut pos = Position::empty();
        pos.place_piece(Piece::knight(Color::White), Square::E4)
            .expect("Failed to place knight on e4");

        let generator = KnightMoveGenerator::new(&pos, Color::White);

        /*
        let bb = generator.bitboard();
        assert_eq!(
            bb,
            BitBoard::new(
                0b00000000_00000000_00000000_00111000_00101000_00111000_00000000_00000000
            )
        );
        */

        let expected_moves = [
            Move::new(Piece::knight(Color::White), Square::E4, Square::C3),
            Move::new(Piece::knight(Color::White), Square::E4, Square::D2),
            Move::new(Piece::knight(Color::White), Square::E4, Square::F2),
            Move::new(Piece::knight(Color::White), Square::E4, Square::G3),
            Move::new(Piece::knight(Color::White), Square::E4, Square::C5),
            Move::new(Piece::knight(Color::White), Square::E4, Square::D6),
            Move::new(Piece::knight(Color::White), Square::E4, Square::G5),
            Move::new(Piece::knight(Color::White), Square::E4, Square::F6),
        ];

        let mut generated_moves: HashSet<Move> = generator.iter().cloned().collect();

        for ex_move in expected_moves {
            assert!(
                generated_moves.remove(&ex_move),
                "{:#?} was not generated",
                &ex_move
            );
        }

        assert!(
            generated_moves.is_empty(),
            "Moves unexpectedly present: {:#?}",
            generated_moves
        );
    }
}