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//! Signed modulo 256-bit integer

use std::convert::{From, Into};
use std::ops::{Div, Rem};
use std::cmp::Ordering;

use super::{Sign, M256};
use super::u256::SIGN_BIT_MASK;

#[derive(Eq, PartialEq, Debug, Copy, Clone, Hash)]
/// Represents a signed module 256-bit integer.
pub struct MI256(Sign, M256);

impl MI256 {
    /// Zero value of MI256.
    pub fn zero() -> MI256 { MI256(Sign::NoSign, M256::zero()) }
    /// One value of MI256.
    pub fn one() -> MI256 { MI256(Sign::Plus, M256::one()) }
    /// Maximum value of MI256.
    pub fn max_value() -> MI256 { MI256(Sign::Plus, M256::max_value() & SIGN_BIT_MASK.into()) }
    /// Minimum value of MI256.
    pub fn min_value() -> MI256 { MI256(Sign::Minus, (M256::max_value() & SIGN_BIT_MASK.into()) + M256::from(1u64)) }
}

impl Default for MI256 { fn default() -> MI256 { MI256::zero() } }
impl From<M256> for MI256 {
    fn from(val: M256) -> MI256 {
        if val == M256::zero() {
            MI256::zero()
        } else if val & SIGN_BIT_MASK.into() == val {
            MI256(Sign::Plus, val)
        } else {
            MI256(Sign::Minus, !val + M256::from(1u64))
        }
    }
}
impl Into<M256> for MI256 {
    fn into(self) -> M256 {
        let sign = self.0;
        if sign == Sign::NoSign {
            M256::zero()
        } else if sign == Sign::Plus {
            self.1
        } else {
            !self.1 + M256::from(1u64)
        }
    }
}

impl Ord for MI256 {
    fn cmp(&self, other: &MI256) -> Ordering {
        match (self.0, other.0) {
            (Sign::NoSign, Sign::NoSign) => Ordering::Equal,
            (Sign::NoSign, Sign::Plus) => Ordering::Less,
            (Sign::NoSign, Sign::Minus) => Ordering::Greater,
            (Sign::Minus, Sign::NoSign) => Ordering::Less,
            (Sign::Minus, Sign::Plus) => Ordering::Less,
            (Sign::Minus, Sign::Minus) => self.1.cmp(&other.1).reverse(),
            (Sign::Plus, Sign::Minus) => Ordering::Greater,
            (Sign::Plus, Sign::NoSign) => Ordering::Greater,
            (Sign::Plus, Sign::Plus) => self.1.cmp(&other.1),
        }
    }
}

impl PartialOrd for MI256 {
    fn partial_cmp(&self, other: &MI256) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl Div for MI256 {
    type Output = MI256;

    fn div(self, other: MI256) -> MI256 {
        if other == MI256::zero() {
            return MI256::zero();
        }

        if self == MI256::min_value() && other == MI256(Sign::Minus, M256::from(1u64)) {
            return MI256::min_value();
        }

        let d = (self.1 / other.1) & SIGN_BIT_MASK.into();

        if d == M256::zero() {
            return MI256::zero();
        }

        match (self.0, other.0) {
            (Sign::Plus, Sign::Plus) |
            (Sign::Minus, Sign::Minus) => MI256(Sign::Plus, d),
            (Sign::Plus, Sign::Minus) |
            (Sign::Minus, Sign::Plus) => MI256(Sign::Minus, d),
            _ => MI256::zero()
        }
    }
}

impl Rem for MI256 {
    type Output = MI256;

    fn rem(self, other: MI256) -> MI256 {
        let r = (self.1 % other.1) & SIGN_BIT_MASK.into();

        if r == M256::zero() {
            return MI256::zero()
        }

        MI256(self.0, r)
    }
}

#[cfg(test)]
mod tests {
    use super::MI256;
    use m256::M256;
    use std::str::FromStr;

    #[test]
    pub fn sdiv() {
        assert_eq!(MI256::from(M256::from_str("8000000000000000000000000000000000000000000000000000000000000000").unwrap()) / MI256::from(M256::from_str("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff").unwrap()), MI256::from(M256::from_str("8000000000000000000000000000000000000000000000000000000000000000").unwrap()));
    }

    #[test]
    pub fn m256() {
        let m256 = M256::from_str("8000000000000000000000000000000000000000000000000000000000000000").unwrap();
        let mi256 = MI256::from(m256);
        let m256b: M256 = mi256.into();
        assert_eq!(m256, m256b);
    }
}