Time zone at a place

use timezone_at.qweruse timezone_at, timezone_all_at from timezone_at      // Quillo 0.6: only these

tzf-rs = "0.4"chrono = { version = "0.4", default-features = false, features = ["std", "clock"] }chrono-tz = "0.10"

// Delivery slots shown in the customer's own time: the time zone of an address's coordinates,// and what time it is there.////   quillo run timezone_at.qwe      then open http://localhost:8080/zone?lat=40.71&lon=-74.0use "timezone_at.qwer"route GET /zone ? { lat: float, lon: float } {    let here = timezone_local(lat, lon, 0)?    { zone: here.zone, offset: here.offset, now_there: here.local }}// 1 July 2026 12:00 UTC at four warehouses: summer time shows in the offsets.route GET /warehouses = [    { city: "Amsterdam", lat: 52.37, lon: 4.89 }, { city: "Sydney", lat: -33.87, lon: 151.21 },    { city: "Phoenix", lat: 33.45, lon: -112.07 }, { city: "Kathmandu", lat: 27.7, lon: 85.32 },] | map((w) => { let t = timezone_local(w.lat, w.lon, 1782907200)?; { city: w.city, zone: t.zone, local: t.local, abbreviation: t.abbreviation } })route GET /sea = { atlantic: timezone_at(30.0, -40.0)?, bad: timezone_at(95.0, 0.0).error }

//! The IANA time zone at a latitude and longitude, offline (no API key, no network): "Europe/Amsterdam" for a delivery address or a photo's GPS, and the local time and UTC offset there.//! version: 1.0.0//!//! [dependencies]//! tzf-rs = "0.4"//! chrono = { version = "0.4", default-features = false, features = ["std", "clock"] }//! chrono-tz = "0.10"use chrono::{Offset, TimeZone, Utc};use serde_json::{json, Value};use std::sync::OnceLock;/// The zone finder, built once (its data is in the library; the first call takes a moment).fn finder() -> &'static tzf_rs::DefaultFinder {    static F: OnceLock<tzf_rs::DefaultFinder> = OnceLock::new();    F.get_or_init(tzf_rs::DefaultFinder::new)}fn check(lat: f64, lon: f64) -> Result<(), String> {    if !(-90.0..=90.0).contains(&lat) || !(-180.0..=180.0).contains(&lon) {        return Err(format!("{}, {} is not a place: latitude is -90 to 90, longitude -180 to 180", lat, lon));    }    Ok(())}/// The time zone's name at a point, such as "America/New_York". At sea it is an `Etc/GMT±n` zone.pub fn timezone_at(lat: f64, lon: f64) -> Result<String, String> {    check(lat, lon)?;    Ok(finder().get_tz_name(lon, lat).to_string())}/// Every zone that claims a point: more than one only where borders are disputed.pub fn timezone_all_at(lat: f64, lon: f64) -> Result<Vec<String>, String> {    check(lat, lon)?;    Ok(finder().get_tz_names(lon, lat).into_iter().map(str::to_string).collect())}/// What time it is at a point, or at the Unix time `at` (seconds; 0 for now): `{ zone, local, offset, offset_minutes, abbreviation }`,/// `local` as `2026-10-29T14:05:00`, `offset` as `+01:00`, summer time counted.pub fn timezone_local(lat: f64, lon: f64, at: i64) -> Result<Value, String> {    check(lat, lon)?;    let name = finder().get_tz_name(lon, lat);    let tz: chrono_tz::Tz = name.parse().map_err(|_| format!("{} is not a zone this library knows", name))?;    let when = if at == 0 { Utc::now() } else { Utc.timestamp_opt(at, 0).single().ok_or(format!("{} is not a time", at))? };    let local = when.with_timezone(&tz);    let secs = local.offset().fix().local_minus_utc();    Ok(json!({        "zone": name, "local": local.format("%Y-%m-%dT%H:%M:%S").to_string(), "offset": local.format("%:z").to_string(),        "offset_minutes": secs / 60, "abbreviation": local.format("%Z").to_string(),    }))}