// Eryn Wells <eryn@erynwells.me>

use super::BitBoard;

impl BitBoard {
    const NOT_A_FILE: u64 = 0xfefe_fefe_fefe_fefe;
    const NOT_H_FILE: u64 = 0x7f7f_7f7f_7f7f_7f7f;

    #[inline]
    pub fn shift_north(&self, n: u8) -> BitBoard {
        BitBoard(self.0 << (8 * n))
    }

    #[inline]
    pub fn shift_north_one(&self) -> BitBoard {
        BitBoard(self.0 << 8)
    }

    #[inline]
    pub fn shift_north_east_one(&self) -> BitBoard {
        BitBoard(self.0 << 9 & BitBoard::NOT_A_FILE)
    }

    #[inline]
    pub fn shift_east(&self, n: u8) -> BitBoard {
        // TODO: Implement a bounds check here.
        BitBoard(self.0 << n)
    }

    #[inline]
    pub fn shift_east_one(&self) -> BitBoard {
        BitBoard(self.0 << 1 & BitBoard::NOT_A_FILE)
    }

    #[inline]
    pub fn shift_south_east_one(&self) -> BitBoard {
        BitBoard(self.0 >> 7 & BitBoard::NOT_A_FILE)
    }

    #[inline]
    pub fn shift_south(&self, n: u8) -> BitBoard {
        BitBoard(self.0 >> (8 * n))
    }

    #[inline]
    pub fn shift_south_one(&self) -> BitBoard {
        BitBoard(self.0 >> 8)
    }

    #[inline]
    pub fn shift_south_west_one(&self) -> BitBoard {
        BitBoard(self.0 >> 9 & BitBoard::NOT_H_FILE)
    }

    #[inline]
    pub fn shift_west_one(&self) -> BitBoard {
        BitBoard(self.0 >> 1 & BitBoard::NOT_H_FILE)
    }

    #[inline]
    pub fn shift_north_west_one(&self) -> BitBoard {
        BitBoard(self.0 << 7 & BitBoard::NOT_H_FILE)
    }
}

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

    #[test]
    fn cardinal_direction_shifts() {
        let bb = BitBoard(0x1000_0000); // e4

        assert_eq!(bb.shift_north_one(), BitBoard(0x0010_0000_0000), "North");
        assert_eq!(bb.shift_east_one(), BitBoard(0x2000_0000), "East");
        assert_eq!(bb.shift_south_one(), BitBoard(0x0010_0000), "South");
        assert_eq!(bb.shift_west_one(), BitBoard(0x0800_0000), "West");
    }

    #[test]
    fn intercardinal_direction_shifts() {
        let bb = BitBoard(0x1000_0000); // e4

        assert_eq!(
            bb.shift_north_east_one(),
            BitBoard(0x0020_0000_0000),
            "North East"
        );
        assert_eq!(
            bb.shift_south_east_one(),
            BitBoard(0x0020_0000),
            "South East"
        );
        assert_eq!(
            bb.shift_south_west_one(),
            BitBoard(0x0008_0000),
            "South West"
        );
        assert_eq!(
            bb.shift_north_west_one(),
            BitBoard(0x0008_0000_0000),
            "North West"
        );
    }

    #[test]
    fn shift_n() {
        assert_eq!(
            BitBoard(0x0008_0000_0000).shift_north(2),
            BitBoard(0x0008_0000_0000_0000)
        );

        assert_eq!(
            BitBoard(0x0008_0000_0000).shift_east(2),
            BitBoard(0x0020_0000_0000)
        );

        assert_eq!(
            BitBoard(0x0008_0000_0000).shift_south(2),
            BitBoard(0x0008_0000)
        );
    }
}