use std::cmp::max;
use std::fmt;
use std::ops::Add;

pub struct Number {
    radix: usize,
    digits: Vec<u8>,
}

impl Number {
    pub fn parse(snum: &str) -> Result<Number, &str> {
        let radix = 10_usize;
        let snum = snum.as_bytes();
        let mut digits = Vec::new();
        for i in (0..snum.len()).rev() {
            let digit = snum[i] - '0' as u8;
            if digit as usize >= radix {
                return Err("Аргумент не является числом");
            } else {
                digits.push(digit);
            }
        }
        return Ok(Number { radix, digits });
    }

    pub fn len(&self) -> usize {
        self.digits.len()
    }
}

impl fmt::Display for Number {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        for i in (0..self.digits.len()).rev() {
            write!(f, "{}", self.digits[i])?;
        }
        return Ok(());
    }
}

impl Add for Number {
    type Output = Self;

    fn add(self, other: Self) -> Self::Output {
        let mut k = 0;
        let len = max(self.len(), other.len());
        let mut digits = Vec::new();
        for i in 0..len {
            let mut digit = 0;
            if i < self.len() {
                digit += self.digits[i] as usize;
            }
            if i < other.len() {
                digit += other.digits[i] as usize;
            }
            digit += k;
            let (div, rem) = (digit / self.radix, digit % self.radix);
            digit = rem;
            k = div;
            digits.push(digit as u8);
        }
        if k != 0 {
            digits.push(k as u8);
        }

        return Number {
            radix: self.radix,
            digits,
        };
    }
}