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use std::str;
use std::str::FromStr;

use crate::arithmetic::sign::Sign;
use crate::arithmetic::sliceops::*;

// converts u64 to string of length 19
fn string_format(x: u64) -> String {
    let k = x.to_string();
    let leading = (0..(19 - k.len())).map(|_| "0").collect::<String>();
    leading + &k
}

// Naive conversion from Radix-2^64 to Radix-10^19 string, very slow
pub(crate) fn to_string(sign: Sign, digits: Vec<u64>) -> String {
    if digits.is_empty() {
        return "".to_string();
    }

    if digits.len() == 1 {
        let p = digits[0].to_string();
        if sign == Sign::Negative {
            return "-".to_owned() + &p;
        } else {
            return p;
        }
    }

    let mut k = vec![];
    let mut x = digits;
    x.push(0u64);
    loop {
        let idx = sig_pos(&x[..]);

        if idx == 0 {
            break;
        }

        k.push(div_slice(&mut x[..idx], 0x8AC7230489E80000u64));
    }
    k.push(x[0] % 0x8AC7230489E80000u64);

    let mut count = 0usize;
    for i in k.iter().rev() {
        if *i > 0u64 {
            break;
        }
        count += 1;
    }

    k.truncate(k.len() - count);

    let len = k.len() - 1;
    let interim = k[..len]
        .iter()
        .rev()
        .map(|x| string_format(*x))
        .collect::<Vec<String>>();
    let last = k[len].to_string() + &interim.join("");

    if sign == Sign::Negative {
        return "-".to_string() + &last;
    }
    last
}

pub(crate) fn from_string(string: &str) -> Option<Vec<u64>> {
    let b = string.bytes().all(|c| c.is_ascii_digit());

    if !b {
        return None;
    }

    let ln = 19usize;
    let strln = string.len();
    let strem = strln % ln;
    let t = string.as_bytes();
    let start = 0usize;

    let mut k = vec![];

    for i in 0..strln / ln {
        k.push(str::from_utf8(&t[(strln - (i + 1) * ln)..(strln - i * ln)]).unwrap())
    }
    if strem != 0 {
        // if there is a remaining slice greater than zero
        if str::from_utf8(&t[start..strem]).unwrap() != "" {
            // if the first value is not empty then it pushes it to the vector
            k.push(str::from_utf8(&t[start..strem]).unwrap());
        }
    }
    let x = k
        .iter()
        .rev()
        .map(|x| u64::from_str(x).unwrap())
        .collect::<Vec<u64>>(); // string converted to decimal vector

    let mut z = vec![0];
    for i in 0..x.len() {
        let mut carry = scale_slice(&mut z[..], 0x8AC7230489E80000);
        if carry > 0 {
            z.push(carry)
        }
        carry = add_slice(&mut z[..], &x[i..(i + 1)]) as u64;
        if carry > 0 {
            z.push(carry)
        }
    }
    Some(z)
}