Code shared from the Rust Playground

playground.rs

use chrono::prelude::*;
use regex::Regex;
#[macro_use]
extern crate lazy_static; // 1.4.0

/// A function when provided with the date in the format
/// YYYY/MM/DD or YYYY-MM-DD returns an output as YYYYMMDD
///     If the date is invalid it returns the today (now) YYYYMMDD
///     Hmm, I think its best to send back as none.
pub fn date_in_cobol_format(text: &str) -> Option<String> {
    regex_date_in_cobol_format(text).map(|c| c.as_cobol())
}
/// A function when provided with the date in the format
/// YYYY/MM/DD or YYYY-MM-DD returns an output as YYYYMMDD
///     If the date is invalid it returns the today (now) YYYYMMDD
///     Hmm, I think its best to send back as none.
pub fn tuples_date_in_cobol_format(text: &str) -> Option<(i32, u32, u32)> {
    regex_date_in_cobol_format(text).map(|c| (c.yyyy(), c.mm(), c.dd()))
}

/// A function when provided with the date in the format
/// YYYY/MM/DD or YYYY-MM-DD returns an output as YYYYMMDD
///     If the date is invalid it returns the today (now) YYYYMMDD
///     Hmm, I think its best to send back as none.
fn regex_date_in_cobol_format(text: &str) -> Option<CobolDate> {
    lazy_static! {
        static ref RE: Regex = Regex::new(
            r"(?x)
(?P<year>\d{4})  # the year
[/.-]
(?P<month>\d{2}) # the month
[/.-]
(?P<day>\d{2})   # the day
"
        )
        .unwrap();
    }

    RE.captures(text).map(|caps| CobolDate {
        yyyy_str: caps["year"].to_string(),
        mm_str: caps["month"].to_string(),
        dd_str: caps["day"].to_string(),
    })
}

#[derive(Debug, Clone)]
struct CobolDate {
    yyyy_str: String,
    mm_str: String,
    dd_str: String,
}

impl CobolDate {
    fn yyyy(&self) -> i32 {
        self.yyyy_str.parse::<i32>().unwrap_or(Utc::today().year())
    }

    fn mm(&self) -> u32 {
        self.mm_str.parse::<u32>().unwrap_or(Utc::today().month())
    }

    fn dd(&self) -> u32 {
        self.dd_str.parse::<u32>().unwrap_or(Utc::today().day())
    }

    fn as_cobol(&self) -> String {
        let y = self.yyyy().clone();
        let m = self.mm().clone();
        let d = self.dd().clone();
        Utc.ymd(y, m, d).and_hms(0, 0, 0).format("%Y%m%d").to_string()
    }
}


fn main() {
    println!("=========== Date !");
    let b = DateTime::parse_from_str("2014-11-28 21:00:09 +09:00", "%Y-%m-%d %H:%M:%S %z").unwrap();
    println!("* {:?}", b.format("%Y/%m/%d").to_string());
   // println!("{:?}", date_in_cobol_format("05/21/1982"));
}