// Eryn Wells <eryn@erynwells.me>

use crate::library;
use crate::{LeadingBitScanner, TrailingBitScanner};
use chessfriend_core::{Color, Direction, File, Rank, Square};
use std::fmt;
use std::ops::Not;

#[derive(Clone, Copy, Eq, Hash, PartialEq)]
pub struct BitBoard(pub(crate) u64);

macro_rules! moves_getter {
    ($getter_name:ident) => {
        pub fn $getter_name(sq: Square) -> BitBoard {
            library::library().$getter_name(sq)
        }
    };
}

impl BitBoard {
    pub const EMPTY: BitBoard = BitBoard(u64::MIN);
    pub const FULL: BitBoard = BitBoard(u64::MAX);

    pub const fn empty() -> BitBoard {
        BitBoard(0)
    }

    pub const fn new(bits: u64) -> BitBoard {
        BitBoard(bits)
    }

    pub fn rank(rank: &u8) -> BitBoard {
        debug_assert!(*rank < 8);
        library::RANKS[*rank as usize]
    }

    pub fn file(file: &u8) -> BitBoard {
        debug_assert!(*file < 8);
        library::FILES[*file as usize]
    }

    pub fn ray(sq: Square, dir: Direction) -> &'static BitBoard {
        library::library().ray(sq, dir)
    }

    pub fn pawn_attacks(sq: Square, color: Color) -> BitBoard {
        library::library().pawn_attacks(sq, color)
    }

    pub fn pawn_pushes(sq: Square, color: Color) -> BitBoard {
        library::library().pawn_pushes(sq, color)
    }

    moves_getter!(knight_moves);
    moves_getter!(bishop_moves);
    moves_getter!(rook_moves);
    moves_getter!(queen_moves);
    moves_getter!(king_moves);

    pub const fn kingside(color: Color) -> &'static BitBoard {
        &library::KINGSIDES[color as usize]
    }

    pub const fn queenside(color: Color) -> &'static BitBoard {
        &library::QUEENSIDES[color as usize]
    }
}

impl BitBoard {
    pub const fn as_bits(&self) -> &u64 {
        &self.0
    }

    /// Returns `true` if the [`BitBoard`] has no bits set.
    ///
    /// ## Examples
    ///
    /// ```
    /// use chessfriend_bitboard::BitBoard;
    /// assert!(BitBoard::EMPTY.is_populated());
    /// assert!(!BitBoard::FULL.is_populated());
    /// assert!(!BitBoard::new(0b1000).is_populated());
    /// ```
    pub const fn is_empty(&self) -> bool {
        self.0 == 0
    }

    /// Returns `true` if the [`BitBoard`] has at least one bit set.
    ///
    /// ## Examples
    ///
    /// ```
    /// use chessfriend_bitboard::BitBoard;
    /// assert!(!BitBoard::EMPTY.is_populated());
    /// assert!(BitBoard::FULL.is_populated());
    /// assert!(BitBoard::new(0b1).is_populated());
    /// ```
    pub const fn is_populated(&self) -> bool {
        self.0 != 0
    }

    /// Returns `true` if this [`BitBoard`] has the bit corresponding to `square` set.
    pub fn is_set(self, square: Square) -> bool {
        let square_bitboard: BitBoard = square.into();
        !(self & square_bitboard).is_empty()
    }

    /// The number of 1 bits in the BitBoard.
    ///
    /// ## Examples
    ///
    /// ```
    /// use chessfriend_bitboard::BitBoard;
    /// assert_eq!(BitBoard::EMPTY.population_count(), 0);
    /// assert_eq!(BitBoard::new(0b01011110010).population_count(), 6);
    /// assert_eq!(BitBoard::FULL.population_count(), 64);
    /// ```
    pub const fn population_count(&self) -> u32 {
        self.0.count_ones()
    }

    pub fn set_square(&mut self, sq: Square) {
        let sq_bb: BitBoard = sq.into();
        *self |= sq_bb
    }

    pub fn clear_square(&mut self, sq: Square) {
        let sq_bb: BitBoard = sq.into();
        *self &= !sq_bb
    }

    /// Returns `true` if this BitBoard represents a single square.
    ///
    /// ## Examples
    ///
    /// ```
    /// use chessfriend_bitboard::BitBoard;
    /// assert!(!BitBoard::EMPTY.is_single_square(), "Empty bitboards represent no squares");
    /// assert!(!BitBoard::FULL.is_single_square(), "Full bitboards represent all the squares");
    /// assert!(!BitBoard::new(0b010011110101101100).is_single_square(), "This bitboard represents a bunch of squares");
    /// assert!(BitBoard::new(0b10000000000000).is_single_square());
    /// ```
    pub fn is_single_square(&self) -> bool {
        self.0.is_power_of_two()
    }
}

impl BitBoard {
    /// Returns an Iterator over the occupied squares.
    ///
    /// The Iterator yields squares starting from the leading (most-significant bit) end of the
    /// board to the trailing (least-significant bit) end.
    #[must_use]
    pub fn occupied_squares(&self) -> impl Iterator<Item = Square> {
        LeadingBitScanner::new(self.0).map(|idx| unsafe { Square::from_index(idx as u8) })
    }

    /// Return an Iterator over the occupied squares, starting from the trailing
    /// (least-significant bit) end of the field.
    #[must_use]
    pub fn occupied_squares_trailing(&self) -> impl Iterator<Item = Square> {
        TrailingBitScanner::new(self.0).map(|idx| unsafe { Square::from_index(idx as u8) })
    }

    #[must_use]
    pub fn first_occupied_square(&self) -> Option<Square> {
        let leading_zeros = self.0.leading_zeros() as u8;
        if leading_zeros < Square::NUM as u8 {
            unsafe { Some(Square::from_index(Square::NUM as u8 - leading_zeros - 1)) }
        } else {
            None
        }
    }

    #[must_use]
    pub fn first_occupied_square_trailing(&self) -> Option<Square> {
        let trailing_zeros = self.0.trailing_zeros() as u8;
        if trailing_zeros < Square::NUM as u8 {
            unsafe { Some(Square::from_index(trailing_zeros)) }
        } else {
            None
        }
    }
}

impl Default for BitBoard {
    fn default() -> Self {
        BitBoard::EMPTY
    }
}

impl From<File> for BitBoard {
    fn from(value: File) -> Self {
        library::FILES[*value.as_index() as usize]
    }
}

impl From<Option<Square>> for BitBoard {
    fn from(value: Option<Square>) -> Self {
        value.map_or(BitBoard::EMPTY, Into::<BitBoard>::into)
    }
}

impl From<Rank> for BitBoard {
    fn from(value: Rank) -> Self {
        library::FILES[*value.as_index() as usize]
    }
}

impl From<Square> for BitBoard {
    fn from(value: Square) -> Self {
        BitBoard(1u64 << value as u32)
    }
}

impl FromIterator<Square> for BitBoard {
    fn from_iter<T: IntoIterator<Item = Square>>(iter: T) -> Self {
        let mut builder = BitBoardBuilder::empty();

        for sq in iter {
            builder = builder.square(sq)
        }

        builder.build()
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum TryFromBitBoardError {
    NotSingleSquare,
}

impl TryFrom<BitBoard> for Square {
    type Error = TryFromBitBoardError;

    fn try_from(value: BitBoard) -> Result<Self, Self::Error> {
        if !value.is_single_square() {
            return Err(TryFromBitBoardError::NotSingleSquare);
        }

        unsafe { Ok(Square::from_index(value.0.trailing_zeros() as u8)) }
    }
}

impl fmt::Binary for BitBoard {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Delegate to u64's implementation of Binary.
        fmt::Binary::fmt(&self.0, f)
    }
}

impl fmt::LowerHex for BitBoard {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Delegate to u64's implementation of LowerHex.
        fmt::LowerHex::fmt(&self.0, f)
    }
}

impl fmt::UpperHex for BitBoard {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Delegate to u64's implementation of UpperHex.
        fmt::UpperHex::fmt(&self.0, f)
    }
}

impl fmt::Display for BitBoard {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let binary_ranks = format!("{:064b}", self.0)
            .chars()
            .rev()
            .map(|c| String::from(c))
            .collect::<Vec<String>>();

        let mut ranks_written = 0;
        for rank in binary_ranks.chunks(8).rev() {
            let joined_rank = rank.join(" ");
            write!(f, "{}", joined_rank)?;

            ranks_written += 1;
            if ranks_written < 8 {
                write!(f, "\n")?;
            }
        }

        Ok(())
    }
}

impl fmt::Debug for BitBoard {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
        write!(f, "BitBoard({:064b})", self.0)
    }
}

macro_rules! infix_op {
    ($trait_type:ident, $func_name:ident, $type:ty) => {
        infix_op!($trait_type, $func_name, $type, $type);
        infix_op!($trait_type, $func_name, $type, &$type);
        infix_op!($trait_type, $func_name, &$type, $type);
        infix_op!($trait_type, $func_name, &$type, &$type);
    };
    ($trait_type:ident, $func_name:ident, $left_type:ty, $right_type:ty) => {
        impl std::ops::$trait_type<$right_type> for $left_type {
            type Output = BitBoard;

            #[inline]
            fn $func_name(self, rhs: $right_type) -> Self::Output {
                BitBoard(std::ops::$trait_type::$func_name(self.0, rhs.0))
            }
        }
    };
}

macro_rules! assign_op {
    ($trait_type:ident, $func_name:ident, $type:ty) => {
        impl std::ops::$trait_type for $type {
            #[inline]
            fn $func_name(&mut self, rhs: $type) {
                std::ops::$trait_type::$func_name(&mut self.0, rhs.0)
            }
        }

        impl std::ops::$trait_type<&$type> for $type {
            #[inline]
            fn $func_name(&mut self, rhs: &$type) {
                std::ops::$trait_type::$func_name(&mut self.0, rhs.0)
            }
        }
    };
}

infix_op!(BitAnd, bitand, BitBoard);
infix_op!(BitOr, bitor, BitBoard);
infix_op!(BitXor, bitxor, BitBoard);

assign_op!(BitAndAssign, bitand_assign, BitBoard);
assign_op!(BitOrAssign, bitor_assign, BitBoard);
assign_op!(BitXorAssign, bitxor_assign, BitBoard);

impl Not for BitBoard {
    type Output = BitBoard;

    #[inline]
    fn not(self) -> Self::Output {
        BitBoard(!self.0)
    }
}

impl Not for &BitBoard {
    type Output = BitBoard;

    #[inline]
    fn not(self) -> Self::Output {
        BitBoard(!self.0)
    }
}


#[cfg(test)]
mod tests {
    use super::*;
    use crate::bitboard;
    use chessfriend_core::Square;

    #[test]
    #[ignore]
    fn display_and_debug() {
        let bb = BitBoard::file(&0) | BitBoard::file(&3) | BitBoard::rank(&7) | BitBoard::rank(&4);
        println!("{}", &bb);
    }

    #[test]
    fn rank() {
        assert_eq!(BitBoard::rank(&0).0, 0xFF, "Rank 1");
        assert_eq!(BitBoard::rank(&1).0, 0xFF00, "Rank 2");
        assert_eq!(BitBoard::rank(&2).0, 0xFF0000, "Rank 3");
        assert_eq!(BitBoard::rank(&3).0, 0xFF000000, "Rank 4");
        assert_eq!(BitBoard::rank(&4).0, 0xFF00000000, "Rank 5");
        assert_eq!(BitBoard::rank(&5).0, 0xFF0000000000, "Rank 6");
        assert_eq!(BitBoard::rank(&6).0, 0xFF000000000000, "Rank 7");
        assert_eq!(BitBoard::rank(&7).0, 0xFF00000000000000, "Rank 8");
    }

    #[test]
    fn is_empty() {
        assert!(BitBoard(0).is_empty());
        assert!(!BitBoard(0xFF).is_empty());
    }

    #[test]
    fn has_piece_at() {
        let bb = BitBoard(0b1001100);
        assert!(bb.is_set(Square::C1));
        assert!(!bb.is_set(Square::B1));
    }

    #[test]
    fn set_square() {
        let sq = Square::E4;
        let mut bb = BitBoard(0b1001100);
        bb.set_square(sq);
        assert!(bb.is_set(sq));
    }

    #[test]
    fn clear_square() {
        let sq = Square::A3;
        let mut bb = BitBoard(0b1001100);
        bb.clear_square(sq);
        assert!(!bb.is_set(sq));
    }

    #[test]
    fn single_rank_occupancy() {
        let bb = BitBoard(0b01010100);
        let expected_squares = [Square::G1, Square::E1, Square::C1];
        for (a, b) in bb.occupied_squares().zip(expected_squares.iter().cloned()) {
            assert_eq!(a, b);
        }
    }

    #[test]
    fn occupancy_spot_check() {
        let bb =
            BitBoard(0b10000000_00000000_00100000_00000100_00000000_00000000_00010000_00001000);

        let expected_squares = [Square::H8, Square::F6, Square::C5, Square::E2, Square::D1];

        for (a, b) in bb.occupied_squares().zip(expected_squares.iter().cloned()) {
            assert_eq!(a, b);
        }
    }

    #[test]
    fn xor() {
        let a = bitboard![C5 G7];
        let b = bitboard![B5 G7 H3];

        assert_eq!(a ^ b, bitboard![B5 C5 H3]);
        assert_eq!(a ^ BitBoard::empty(), a);
        assert_eq!(BitBoard::empty() ^ BitBoard::empty(), BitBoard::empty());
    }

    #[test]
    fn bitand_assign() {
        let mut a = bitboard![C5 G7];
        let b = bitboard![B5 G7 H3];

        a &= b;

        assert_eq!(a, bitboard![G7]);
    }

    #[test]
    fn bitor_assign() {
        let mut a = bitboard![C5 G7];
        let b = bitboard![B5 G7 H3];

        a |= b;

        assert_eq!(a, bitboard![B5 C5 G7 H3]);
    }

    #[test]
    fn from_square() {
        assert_eq!(BitBoard::from(Square::A1), BitBoard(0b1));
        assert_eq!(BitBoard::from(Square::H8), BitBoard(1 << 63));
    }

    #[test]
    fn first_occupied_squares() {
        let bb = bitboard![A8 E1];
        assert_eq!(bb.first_occupied_square(), Some(Square::A8));
        assert_eq!(bb.first_occupied_square_trailing(), Some(Square::E1));

        let bb = bitboard![D6 E7 F8];
        assert_eq!(bb.first_occupied_square_trailing(), Some(Square::D6));
    }
}