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use crate::Square;
use std::ops::{BitAnd, BitOr, BitXor};

const BIT_BOARD_FULL: u128 =
    0b_111111111_111111111_111111111_111111111_111111111_111111111_111111111_111111111_111111111;

#[derive(Clone, Copy)]
pub struct Bitboard(pub u128);

impl BitAnd for Bitboard {
    type Output = Bitboard;

    fn bitand(self, rhs: Self) -> Self::Output {
        Self(self.0 & rhs.0)
    }
}

impl BitOr for Bitboard {
    type Output = Bitboard;

    fn bitor(self, rhs: Self) -> Self::Output {
        Self(self.0 | rhs.0)
    }
}

impl BitXor for Bitboard {
    type Output = Bitboard;

    fn bitxor(self, rhs: Self) -> Self::Output {
        Self(self.0 ^ rhs.0)
    }
}

impl Bitboard {
    pub const fn empty() -> Self {
        Self(0)
    }
    pub const fn full() -> Self {
        Self(BIT_BOARD_FULL)
    }

    pub fn is_filled(&self, sq: &Square) -> bool {
        let pos = sq_to_pos(sq);
        self.0 & (1 << pos) != 0
    }
    pub fn fill(&mut self, sq: &Square) {
        let pos = sq_to_pos(sq);
        assert_eq!(self.0 & (1 << pos), 0);
        self.0 ^= 1 << pos;
    }
    pub fn remove(&mut self, sq: &Square) {
        let pos = sq_to_pos(sq);
        assert_ne!(self.0 & (1 << pos), 0);
        self.0 ^= 1 << pos;
    }

    pub fn rotate180(&self) -> Self {
        let reversed = self.0.reverse_bits();
        Bitboard(reversed >> 47)
    }

    pub fn iter(&self) -> impl Iterator<Item = u32> {
        BitIterator(self.0)
    }

    pub fn file_count_ones(&self, file: u8) -> u32 {
        let file_only = super::bit_file(file) & self.0;
        file_only.count_ones()
    }
}

struct BitIterator(u128);

impl Iterator for BitIterator {
    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {
        if self.0 == 0 {
            None
        } else {
            let pos = self.0.trailing_zeros();
            self.0 ^= 1 << pos;
            Some(pos)
        }
    }
}

fn sq_to_pos(sq: &Square) -> u8 {
    (sq.rank - 1) * 9 + 9 - sq.file
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_rotate180() {
        let input: u128 =
            0b_101001000100001000001000000100000001000000001000000000100000000001000000000001000;
        let expected: u128 =
            0b_000100000000000100000000001000000000100000000100000001000000100000100001000100101;
        assert_eq!(expected, Bitboard(input).rotate180().0);
        assert_eq!(input, Bitboard(input).rotate180().rotate180().0);
    }

    #[test]
    fn test_bit_iterator() {
        let v = Bitboard(0b1000100101).iter().collect::<Vec<_>>();
        assert_eq!(v, [0, 2, 5, 9]);
    }

    #[test]
    fn test_full_bit() {
        let full = Bitboard::full();
        assert_eq!(81, full.0.count_ones());
    }
}