build.rs

use std::env;
use std::fs::File;
use std::io::{BufRead, BufReader, BufWriter, Write};
use std::path::Path;
use regex::Regex;
use chrono::{FixedOffset};

const HOUR: u32 = 3600;

fn parse_offset(raw_offset: &str) -> i32 {
    let is_west = raw_offset.starts_with('−');
    let hours = raw_offset[1..3].parse::<u32>().unwrap();
    let minutes = match raw_offset.contains(':') {
        true => raw_offset[4..6].parse::<u32>().unwrap(),
        false => 0,
    };

    let value = (hours * HOUR) + (minutes * 60);
    return if is_west { value as i32 * -1 } else { value as i32 };
}

fn main() {
    let path = Path::new(&env::var("OUT_DIR").unwrap()).join("codegen.rs");
    let raw_tz = BufReader::new(File::open("./src/abbr_tz").unwrap());
    let re = Regex::new(r"([A-Z]+)\s\t.+\s\tUTC([−+±]\d{2}(?::\d{2})?)").unwrap();

    let mut file = BufWriter::new(File::create(&path).unwrap());

    let mut builder: phf_codegen::Map<String> = phf_codegen::Map::new();
    let mut entries: Vec<(String, String)> = vec!();

    for line in raw_tz.lines() {
        let line = line.unwrap();
        // println!("{line}");
        let capture = re.captures(&line).expect("RegEx failed to match line");
        let abbreviation = capture.get(1).unwrap().as_str();


        let offset = if line.starts_with('±') {
            parse_offset(capture.get(2).unwrap().as_str())
        } else {
            0
        };

        builder.entry(String::from(abbreviation), &offset.to_string());
    }

    write!(
        &mut file,
        "static TIMEZONES: phf::Map<&'static str, &'static str> = {}",
        builder.build()
    )
        .unwrap();
    write!(&mut file, ";\n").unwrap();
}