use std::{
    cmp::Ordering,
    convert::From,
    fmt,
    hash::{Hash, Hasher},
    ops::{
        Add, AddAssign, BitAnd, BitOr, BitXor, Deref, DerefMut, Div, DivAssign, Mul, MulAssign,
        Rem, RemAssign, Shl, Shr, Sub, SubAssign,
    },
    str::FromStr,
};

#[derive(Debug, Clone, Copy)]
pub struct BigInt<const N: usize> {
    bytes: [u8; N],
    len: usize,
}

impl<const N: usize> BigInt<N> {
    pub fn from_bytes(bytes: &[u8]) -> Self {
        debug_assert!(bytes.len() != 0);
        let mut len = bytes.len();
        while len > 1 && bytes[len - 1] == 0 {
            len -= 1;
        }
        let mut arr = [0u8; N];
        arr[..len].copy_from_slice(&bytes[..len]);
        BigInt { bytes: arr, len }
    }

    pub fn from_u64(value: u64) -> Self {
        Self::from_bytes(&value.to_le_bytes())
    }

    fn trim_zeros(mut self) -> Self {
        while self.len > 1 && self.bytes[self.len - 1] == 0 {
            self.len -= 1;
        }
        self
    }

    pub fn max_value() -> Self {
        let mut arr = [0u8; N];
        arr.fill(255);
        BigInt { bytes: arr, len: N }
    }
    pub fn div_rem(&self, other: &Self) -> (Self, Self) {
        let mut quotient = BigInt::from(0);
        let mut remainder = self.clone();
        let divisor = other.clone();

        while remainder >= divisor {
            let mut multiple = divisor.clone();
            let mut temp_quotient = BigInt::from(1);
            while multiple + multiple <= remainder {
                multiple = multiple + multiple;
                temp_quotient = temp_quotient + temp_quotient;
            }
            remainder = remainder - multiple;
            quotient = quotient + temp_quotient;
        }
        (quotient.trim_zeros(), remainder.trim_zeros())
    }
}

impl<const N: usize> Add for BigInt<N> {
    type Output = Self;
    fn add(self, rhs: Self) -> Self {
        let mut result = [0u8; N];
        let mut carry = 0u16;
        let max_len = self.len.max(rhs.len);
        let mut res_len = 0;

        for i in 0..max_len {
            let a = self.bytes.get(i).copied().unwrap_or(0) as u16;
            let b = rhs.bytes.get(i).copied().unwrap_or(0) as u16;
            let sum = a + b + carry;
            result[i] = (sum % 256) as u8;
            carry = sum / 256;
            res_len = i + 1;
        }

        if carry > 0 {
            result[res_len] = carry as u8;
            res_len += 1;
        }

        BigInt {
            bytes: result,
            len: res_len,
        }
        .trim_zeros()
    }
}

impl<const N: usize> AddAssign for BigInt<N> {
    fn add_assign(&mut self, rhs: Self) {
        *self = *self + rhs;
    }
}

impl<const N: usize> Sub for BigInt<N> {
    type Output = Self;
    fn sub(self, rhs: Self) -> Self {
        let mut result = [0u8; N];
        let mut borrow = 0i16;
        let mut res_len = 0;

        for i in 0..self.len {
            let a = self.bytes[i] as i16;
            let b = rhs.bytes.get(i).copied().unwrap_or(0) as i16;
            let mut diff = a - b - borrow;
            borrow = 0;

            if diff < 0 {
                diff += 256;
                borrow = 1;
            }

            result[i] = diff as u8;
            res_len = i + 1;
        }

        BigInt {
            bytes: result,
            len: res_len,
        }
        .trim_zeros()
    }
}

impl<const N: usize> SubAssign for BigInt<N> {
    fn sub_assign(&mut self, rhs: Self) {
        *self = *self - rhs;
    }
}

impl<const N: usize> Mul for BigInt<N> {
    type Output = Self;
    fn mul(self, rhs: Self) -> Self {
        let mut result = BigInt {
            bytes: [0; N],
            len: 0,
        };

        for i in 0..self.len {
            let mut carry = 0u16;
            for j in 0..rhs.len {
                let idx = i + j;
                if idx >= N {
                    panic!("Multiplication overflow");
                }
                let product =
                    self.bytes[i] as u16 * rhs.bytes[j] as u16 + carry + result.bytes[idx] as u16;
                result.bytes[idx] = (product % 256) as u8;
                carry = product / 256;
            }
            let mut k = i + rhs.len;
            while carry > 0 && k < N {
                let sum = result.bytes[k] as u16 + carry;
                result.bytes[k] = (sum % 256) as u8;
                carry = sum / 256;
                k += 1;
            }
            result.len = result.len.max(k);
        }

        result.trim_zeros()
    }
}

impl<const N: usize> MulAssign for BigInt<N> {
    fn mul_assign(&mut self, rhs: Self) {
        *self = *self * rhs;
    }
}

impl<const N: usize> Div for BigInt<N> {
    type Output = Self;
    fn div(self, rhs: Self) -> Self {
        self.div_rem(&rhs).0
    }
}

impl<const N: usize> DivAssign for BigInt<N> {
    fn div_assign(&mut self, rhs: Self) {
        *self = *self / rhs;
    }
}

impl<const N: usize> Rem for BigInt<N> {
    type Output = Self;
    fn rem(self, rhs: Self) -> Self {
        self.div_rem(&rhs).1
    }
}

impl<const N: usize> RemAssign for BigInt<N> {
    fn rem_assign(&mut self, rhs: Self) {
        *self = *self % rhs;
    }
}

impl<const N: usize> PartialEq for BigInt<N> {
    fn eq(&self, other: &Self) -> bool {
        self.bytes[..self.len] == other.bytes[..other.len]
    }
}

impl<const N: usize> Eq for BigInt<N> {}

impl<const N: usize> Hash for BigInt<N> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.bytes[..self.len].hash(state);
    }
}

impl<const N: usize> PartialOrd for BigInt<N> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl<const N: usize> Ord for BigInt<N> {
    fn cmp(&self, other: &Self) -> Ordering {
        if self.len != other.len {
            return self.len.cmp(&other.len);
        }
        for i in (0..self.len).rev() {
            match self.bytes[i].cmp(&other.bytes[i]) {
                Ordering::Equal => continue,
                ord => return ord,
            }
        }
        Ordering::Equal
    }
}

impl<const N: usize> Deref for BigInt<N> {
    type Target = [u8];
    fn deref(&self) -> &[u8] {
        &self.bytes[..self.len]
    }
}

impl<const N: usize> DerefMut for BigInt<N> {
    fn deref_mut(&mut self) -> &mut [u8] {
        &mut self.bytes[..self.len]
    }
}

macro_rules! impl_from_int {
    ($($t:ty),*) => {$(
        impl<const N: usize> From<$t> for BigInt<N> {
            fn from(value: $t) -> Self {
                let bytes = value.to_le_bytes();
                Self::from_bytes(&bytes)
            }
        }
    )*};
}

impl_from_int!(i8, u8, i16, u16, i32, u32, i64, u64, i128, u128);

impl<const N: usize> FromStr for BigInt<N> {
    type Err = &'static str;
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let mut result = BigInt::from(0u8);
        for c in s.chars() {
            if !c.is_digit(10) {
                return Err("Invalid digit");
            }
            let digit = c.to_digit(10).unwrap() as u8;
            result = result * BigInt::from(10u8) + BigInt::from(digit);
        }
        Ok(result)
    }
}

impl<const N: usize> fmt::Display for BigInt<N> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        if self.len == 0 {
            return write!(f, "0");
        }
        let mut digits = Vec::new();
        let mut bytes = self.bytes[..self.len].to_vec();

        while !bytes.is_empty() {
            let mut remainder = 0u16;
            for byte in bytes.iter_mut().rev() {
                let value = *byte as u16 + remainder * 256;
                *byte = (value / 10) as u8;
                remainder = value % 10;
            }
            digits.push(remainder as u8);
            while !bytes.is_empty() && bytes[bytes.len() - 1] == 0 {
                bytes.pop();
            }
        }

        digits.reverse();
        let s = digits
            .iter()
            .map(|d| char::from_digit(*d as u32, 10).unwrap())
            .collect::<String>();
        write!(f, "{}", s)
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Hash, Default)]
struct Dint {
    bytes: Vec<u8>,
}

impl Deref for Dint {
    type Target = [u8];
    fn deref(&self) -> &[u8] {
        &self.bytes
    }
}

impl DerefMut for Dint {
    fn deref_mut(&mut self) -> &mut [u8] {
        &mut self.bytes
    }
}

pub fn main() {
    type TheInt = BigInt<2>;
    let mut test: TheInt = TheInt::max_value();
    let thing = BigInt::<9>::max_value();
    test /= 2.into();
    println!("{test}")
}