// Eryn Wells <eryn@erynwells.me>

use super::library::{library, FILES, RANKS};
use super::{LeadingBitScanner, TrailingBitScanner};
use crate::{square::Direction, Square};
use std::fmt;
use std::ops::{BitAnd, BitAndAssign, BitOr, BitOrAssign, Not};

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

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

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

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

    pub fn rank(rank: usize) -> BitBoard {
        assert!(rank < 8);
        RANKS[rank]
    }

    pub fn file(file: usize) -> BitBoard {
        assert!(file < 8);
        FILES[file]
    }

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

    pub fn is_empty(&self) -> bool {
        self.0 == 0
    }

    pub fn has_piece_at(self, sq: Square) -> bool {
        !(self & sq.into()).is_empty()
    }

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

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

impl BitBoard {
    /// Return an Iterator over the occupied squares, starting from the leading
    /// (most-significant bit) end of the field.
    pub(crate) fn occupied_squares(&self) -> impl Iterator<Item = Square> {
        LeadingBitScanner::new(self.0).map(Square::from_index)
    }

    /// Return an Iterator over the occupied squares, starting from the trailing
    /// (least-significant bit) end of the field.
    pub(crate) fn occupied_squares_trailing(&self) -> impl Iterator<Item = Square> {
        LeadingBitScanner::new(self.0).map(Square::from_index)
    }
}

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

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> {
        f.debug_tuple("BitBoard")
            .field(&format_args!("{:064b}", self.0))
            .finish()
    }
}

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

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

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

infix_op!(BitAnd, bitand, BitBoard, BitBoard);

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

infix_op!(BitOr, bitor, BitBoard, 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::Square;

    #[test]
    fn display_and_debug() {
        let bb = BitBoard::file(0) | BitBoard::file(3) | BitBoard::rank(7) | BitBoard::rank(4);
        println!("{}", &bb);
        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.has_piece_at(Square::C1));
        assert!(!bb.has_piece_at(Square::B1));
    }

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

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