tzconvert/src/lib.rs

use chrono::prelude::*;
use chrono_tz::Tz;

lazy_static::lazy_static! {
    static ref HOUR_AMPM: regex::Regex = regex::Regex::new(r#"(?P<hr>\d{1,2})\s?(?P<ampm>(am|pm|AM|PM))"#).unwrap();
    static ref HOUR_MINUTE_AMPM: regex::Regex = regex::Regex::new(r#"(?P<hr>\d{1,2}):(?P<minute>\d{2})\s?(?P<ampm>(am|pm|AM|PM))"#).unwrap();
}

fn parse_time(time_input: &str) -> NaiveTime {
    let time: String = time_input.split_whitespace().collect::<Vec<_>>().join("");
    match NaiveTime::parse_from_str(&time, "%H:%M") {
        Ok(t) => return t,
        Err(_e) => {}
    }

    if HOUR_MINUTE_AMPM.is_match(&time) {
        return NaiveTime::parse_from_str(&time, "%I:%M%p").unwrap();
    }

    let t2 = HOUR_AMPM.replace(&time, "$hr:00$ampm");

    match NaiveTime::parse_from_str(&t2, "%I:%M%p") {
        Ok(t) => return t,
        Err(_e) => {}
    }

    panic!("failed to parse time -- try HH:MM format (input = '{}')", time)
}

fn convert_common_tz_abbrs(tz: &str) -> &str {
    let tz = tz.trim();
    if tz.eq_ignore_ascii_case("EST") { return "America/New_York" }
    if tz.eq_ignore_ascii_case("EPT") { return "America/New_York" }
    if tz.eq_ignore_ascii_case("EDT") { return "America/New_York" }
    if tz.eq_ignore_ascii_case("US/Eastern") { return "America/New_York" }
    if tz.eq_ignore_ascii_case("CET") { return "Europe/Brussels" }
    if tz.eq_ignore_ascii_case("CEST") { return "Europe/Brussels" }
    if tz.eq_ignore_ascii_case("Brussels") { return "Europe/Brussels" }

    tz
}

pub fn convert(from: &str, to: &str, time: &str, date: Option<NaiveDate>) {
    let from = convert_common_tz_abbrs(from);
    let to = convert_common_tz_abbrs(to);

    let fromtz: Tz = match from.parse() {
        Ok(tz) => tz,
        Err(e) => panic!("failed to parse from tz: {} (input = '{}')", e, from),
    };

    let totz: Tz = match to.parse() {
        Ok(tz) => tz,
        Err(e) => panic!("failed to parse to tz: {} (input = '{}')", e, to),
    };

    let tm = parse_time(time);

    let dt: Date<Tz> = match date {
        Some(dt) => fromtz.from_local_date(&dt).unwrap(),
        None => Utc::today().with_timezone(&fromtz),
    };

    let src = dt.and_time(tm).unwrap();

    let dst = src.with_timezone(&totz);

    let fromtz_str = fromtz.to_string();
    let totz_str = totz.to_string();
    let n_spaces = std::cmp::max(fromtz_str.len(), totz_str.len());

    let indent = "    ";
    println!();
    println!("{} {} ... {} ... {}",
        indent,
        pad_spaces(fromtz_str, n_spaces),
        src.format("%a, %b %e"),
        src.format("%l:%M%P"),
    );

    println!();

    println!("{} {} ... {} ... {}",
        indent,
        pad_spaces(totz_str, n_spaces),
        dst.format("%a, %b %e"),
        dst.format("%l:%M%P"),
    );

    println!();
}

fn pad_spaces<S: ToString>(s: S, n: usize) -> String {
    let s = s.to_string();
    let mut out = String::with_capacity(n);
    out.push_str(&s);
    while out.len() < n {
        out.push_str(" ");
    }
    out
}

#[test]
fn parse_time_like_2pm() {
    dbg!(parse_time("2pm"));
    assert_eq!(parse_time("2pm"), NaiveTime::from_hms(14, 0, 0));
    assert_eq!(parse_time("7am"), NaiveTime::from_hms(7, 0, 0));
    dbg!(HOUR_AMPM.replace("8:30am", "$hr:00$ampm"));
    assert_eq!(parse_time("8:30am"), NaiveTime::from_hms(8, 30, 0));
}