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// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

//! Types for resolving and manipulating time zones.
//!
//! # Fields
//!
//! In ICU4X, a [formattable time zone](CustomTimeZone) consists of four different fields:
//!
//! 1. The offset from GMT
//! 2. The time zone ID
//! 3. The metazone ID
//! 4. The zone variant (standard or daylight time)
//!
//! ## GMT Offset
//!
//! The GMT offset precisely states the time difference between the time zone in question and
//! Greenwich Mean Time (GMT) or Coordinated Universal Time (UTC).
//!
//! In localized strings, it is often rendered as "GMT-6", meaning 6 hours less than GMT.
//!
//! ## Time Zone
//!
//! The time zone ID corresponds to a time zone from the time zone database. The time zone ID
//! usually corresponds to the largest city in the time zone.
//!
//! There are two mostly-interchangeable standards for time zone IDs:
//!
//! 1. IANA time zone IDs, like `"America/Chicago"`
//! 2. BCP-47 time zone IDs, like `"uschi"`
//!
//! ICU4X uses BCP-47 time zone IDs for all of its APIs.
//!
//! ## Metazone
//!
//! A metazone is a collection of multiple time zones that share the same localized formatting
//! at a particular date and time.
//!
//! For example, "America/Chicago" and "America/Indiana/Knox" both map to US Central Time, or
//! `"America_Central"`.
//!
//! The mapping from time zone to metazone depends on the date. For example, from 1991 to 2006,
//! "America/Indiana/Knox" mapped to US Eastern Time instead of US Central Time.
//!
//! As with time zone IDs, there are two interchangeable forms:
//!
//! 1. Long form, like `"America_Central"`
//! 2. Short form compatible with BCP-47, like `"amce"`
//!
//! ICU4X uses the short form.
//!
//! Note: in ICU4X, "metazone" is one word and "time zone" is two words, except for this crate
//! and module name, where "timezone" is used with no separators.
//!
//! ## Zone Variant
//!
//! Many metazones use different names and offsets in the summer than in the winter. In ICU4X,
//! this is called the _zone variant_. There are two zone variants:
//!
//! 1. `"dt"` = daylight or summer time
//! 2. `"st"` = standard or winter time
//!
//! Note: It is optional (not required) to set the zone variant when constructing a
//! [`CustomTimeZone`]. Therefore, the list of possible variants does not include a generic variant
//! to represent the lack of a preference.
//!
//! # Calculations
//!
//! In date/time processing, normally only a subset of information is available, and the other
//! fields must be computed from it.
//!
//! The following calculations are currently supported or will be supported:
//!
//! 1. Time Zone + Local DateTime → Meta Zone ([`MetazoneCalculator`])
//! 2. Time Zone + Absolute Time → Offset + Zone Variant (not yet supported)
//!
//! # Examples
//!
//! Create a time zone for which the offset and time zone ID are already known, and calculate
//! the metazone based on a certain local datetime:
//!
//! ```
//! use icu_calendar::DateTime;
//! use icu_timezone::CustomTimeZone;
//! use icu_timezone::GmtOffset;
//! use icu_timezone::MetazoneCalculator;
//! use tinystr::TinyAsciiStr;
//!
//! // Create a time zone for America/Chicago at GMT-6:
//! let mut time_zone = CustomTimeZone::new_empty();
//! time_zone.gmt_offset = "-0600".parse::<GmtOffset>().ok();
//! time_zone.time_zone_id =
//!     "uschi".parse::<TinyAsciiStr<8>>().ok().map(Into::into);
//!
//! // Compute the metazone at January 1, 2022:
//! let mzc = MetazoneCalculator::try_new_unstable(&icu_testdata::unstable())
//!     .unwrap();
//! let datetime = DateTime::try_new_iso_datetime(2022, 1, 1, 0, 0, 0).unwrap();
//! time_zone.maybe_calculate_metazone(&mzc, &datetime);
//!
//! assert_eq!("amce", time_zone.metazone_id.unwrap().0.as_str());
//! ```

// https://github.com/unicode-org/icu4x/blob/main/docs/process/boilerplate.md#library-annotations
#![cfg_attr(not(any(test, feature = "std")), no_std)]
#![cfg_attr(
    not(test),
    deny(
        clippy::indexing_slicing,
        clippy::unwrap_used,
        clippy::expect_used,
        clippy::panic,
        clippy::exhaustive_structs,
        clippy::exhaustive_enums,
        missing_debug_implementations,
    )
)]
#![warn(missing_docs)]

extern crate alloc;

mod error;
mod metazone;
pub mod provider;
mod time_zone;
mod types;

pub use error::TimeZoneError;
pub use metazone::MetazoneCalculator;
pub use provider::{MetazoneId, TimeZoneBcp47Id};
pub use time_zone::CustomTimeZone;
pub use types::{GmtOffset, ZoneVariant};

#[doc(no_inline)]
pub use TimeZoneError as Error;