big-rational-str 0.1.0

#[cfg(test)]
mod tests;

use std::collections::HashMap;
use std::fmt::Write;
use std::str::FromStr;
use num::{BigRational, FromPrimitive, BigInt, Zero, One};
use regex::{Regex, Captures};

lazy_static::lazy_static! {
    static ref TEN: BigInt = BigInt::from_u32(10).unwrap();
    static ref NINE: BigInt = BigInt::from_u32(9).unwrap();
    static ref REGEX: Regex = Regex::new(r"^(?P<int>\d+)(\.(?P<frac>\d*)(\((?P<repeat>\d+)\))?)?$").unwrap();
}

pub fn big_rational_to_str(n: BigRational) -> String {
    let mut fraction = String::new();
    let mut map = HashMap::new();
    let mut rem = n.numer() % n.denom();
    while !rem.is_zero() && !map.contains_key(&rem) {
        map.insert(rem.clone(), fraction.len());
        rem *= TEN.clone();
        fraction.push_str(&(rem.clone() / n.denom()).to_string());
        rem = rem % n.denom();
    }
    let mut output = (n.numer() / n.denom()).to_string();
    if rem.is_zero() {
        if fraction.len() != 0 {
            write!(output, ".{}", &fraction);
        }
    } else {
        write!(output, ".{}({})", &fraction[..map[&rem]], &fraction[map[&rem]..]);
    }
    output
}

pub fn str_to_big_rational(mut string: &str) -> Result<BigRational, ()> {
    match REGEX.captures(string) {
        Some(captures) => {
            let int = &captures["int"];
            let fraction = captures.name("frac").map(|a| a.as_str());
            let repeating = captures.name("repeat").map(|a| a.as_str());

            Ok(match fraction {
                None => BigRational::from_str(int).unwrap(),
                Some(fraction) => match repeating {
                    None => frac(int, fraction),
                    Some(repeating) => repeat(int, fraction, repeating)
                }
            })
        }
        None => Err(())
    }

}


fn frac(integer: &str, fractional: &str) -> BigRational {
    let mut a = BigInt::one();
    for _ in 0..fractional.len() {
        a *= &*TEN;
    }
    BigRational::new(BigInt::from_str(fractional).unwrap(), a) + BigInt::from_str(integer).unwrap()
}

fn repeat(integer: &str, fractional: &str, repeating: &str) -> BigRational {
    let mut a = BigRational::one();
    for _ in 0..fractional.len() {
        a *= &*TEN;
    }
    let b = match BigRational::from_str(fractional) {
        Ok(a) => a,
        Err(_) => BigRational::zero()
    } / &a;
    let mut c = NINE.clone();
    for _ in 1..repeating.len() {
        c *= &*TEN;
        c += &*NINE;
    }
    let d = BigRational::from_str(repeating).unwrap() / c / a;
    b + d + BigInt::from_str(integer).unwrap()
}