// 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 ).

//! Tools for parsing Windows timezone IDs.

use core::fmt::Write;
use icu_locale_core::subtags::{Region, region};
use icu_provider::{DataError, DataPayload, DataProvider};

use crate::{
    TimeZone,
    provider::windows::{TimezoneIdentifiersWindowsV1, WindowsZonesToBcp47Map},
};

/// A mapper between Windows time zone identifier and a BCP-47 ID.
///
/// This mapper currently only supports mapping from windows time zone identifiers
/// to BCP-47 identifiers.
///
/// A windows time zone may vary depending on an associated territory/region. This is represented
/// by the internal data mapping by delimiting the windows time zone and territory/region
/// code with a "/".
///
/// For instance, Central Standard Time can vary depending on the provided regions listed below:
///
/// - Central Standard Time/001
/// - Central Standard Time/US
/// - Central Standard Time/CA
/// - Central Standard Time/MX
/// - Central Standard Time/ZZ
///
/// As such, a [`Region`] may be provided to further specify a desired territory/region when
/// querying a BCP-47 identifier. If no region is provided or the specificity is not required,
/// then the territory will default to the M.49 World Code, `001`.
#[derive(Debug)]
pub struct WindowsParser {
    data: DataPayload<TimezoneIdentifiersWindowsV1>,
}

impl WindowsParser {
    /// Creates a new static [`WindowsParserBorrowed`].
    #[expect(clippy::new_ret_no_self)]
    #[cfg(feature = "compiled_data")]
    pub fn new() -> WindowsParserBorrowed<'static> {
        WindowsParserBorrowed::new()
    }

    icu_provider::gen_buffer_data_constructors!(() -> error: DataError,
        functions: [
            new: skip,
            try_new_with_buffer_provider,
            try_new_unstable,
            Self,
        ]
    );

    #[doc = icu_provider::gen_buffer_unstable_docs!(UNSTABLE, Self::new)]
    pub fn try_new_unstable<P>(provider: &P) -> Result<Self, DataError>
    where
        P: DataProvider<TimezoneIdentifiersWindowsV1> + ?Sized,
    {
        let data = provider.load(Default::default())?.payload;
        Ok(Self { data })
    }

    /// Returns the borrowed version of the mapper that can be queried from
    /// the owned mapper.
    ///
    /// Using the borrowed version allows one to avoid a small potential
    /// indirection cost when querying the mapper from the owned version.
    pub fn as_borrowed(&self) -> WindowsParserBorrowed<'_> {
        WindowsParserBorrowed {
            data: self.data.get(),
        }
    }
}

/// A borrowed wrapper around the windows time zone mapper data.
#[derive(Debug, Copy, Clone)]
pub struct WindowsParserBorrowed<'a> {
    data: &'a WindowsZonesToBcp47Map<'a>,
}

impl WindowsParserBorrowed<'static> {
    /// Cheaply converts a [`WindowsParserBorrowed<'static>`] into a [`WindowsParser`].
    ///
    /// Note: Due to branching and indirection, using [`WindowsParser`] might inhibit some
    /// compile-time optimizations that are possible with [`WindowsParserBorrowed`].
    pub fn static_to_owned(&self) -> WindowsParser {
        WindowsParser {
            data: DataPayload::from_static_ref(self.data),
        }
    }
}

#[cfg(feature = "compiled_data")]
impl Default for WindowsParserBorrowed<'_> {
    fn default() -> Self {
        Self::new()
    }
}

impl WindowsParserBorrowed<'_> {
    /// Creates a new static [`WindowsParserBorrowed`].
    #[cfg(feature = "compiled_data")]
    pub fn new() -> Self {
        WindowsParserBorrowed {
            data: crate::provider::Baked::SINGLETON_TIMEZONE_IDENTIFIERS_WINDOWS_V1,
        }
    }

    /// Returns the BCP-47 ID for a provided Windows time zone and [`Region`] with a case sensitive query.
    ///
    /// If no region is provided or the specificity is not required,
    /// then the territory will default to the M.49 World Code, `001`.
    ///
    /// ```rust
    /// use icu::locale::subtags::{region, subtag};
    /// use icu::time::{TimeZone, zone::WindowsParser};
    ///
    /// let win_tz_mapper = WindowsParser::new();
    ///
    /// let bcp47_id = win_tz_mapper.parse("Central Standard Time", None);
    /// assert_eq!(bcp47_id, Some(TimeZone(subtag!("uschi"))));
    ///
    /// let bcp47_id =
    ///     win_tz_mapper.parse("Central Standard Time", Some(region!("US")));
    /// assert_eq!(bcp47_id, Some(TimeZone(subtag!("uschi"))));
    ///
    /// let bcp47_id =
    ///     win_tz_mapper.parse("Central Standard Time", Some(region!("CA")));
    /// assert_eq!(bcp47_id, Some(TimeZone(subtag!("cawnp"))));
    /// ```
    pub fn parse(self, windows_tz: &str, region: Option<Region>) -> Option<TimeZone> {
        self.parse_from_utf8(windows_tz.as_bytes(), region)
    }

    /// See [`Self::parse`].
    pub fn parse_from_utf8(self, windows_tz: &[u8], region: Option<Region>) -> Option<TimeZone> {
        let mut cursor = self.data.map.cursor();
        // Returns None if input is non-ASCII
        for &byte in windows_tz {
            cursor.step(byte);
        }
        cursor.step(b'/');
        cursor
            .write_str(region.unwrap_or(region!("001")).as_str())
            // region is valid ASCII, but we can do this instead of unwrap
            .ok()?;
        self.data.bcp47_ids.get(cursor.take_value()?)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use icu_locale_core::subtags::subtag;

    #[test]
    fn basic_windows_tz_lookup() {
        let win_map = WindowsParser::new();

        let result = win_map.parse("Central Standard Time", None);
        assert_eq!(result, Some(TimeZone(subtag!("uschi"))));

        let result = win_map.parse("Eastern Standard Time", None);
        assert_eq!(result, Some(TimeZone(subtag!("usnyc"))));

        let result = win_map.parse("Eastern Standard Time", Some(region!("CA")));
        assert_eq!(result, Some(TimeZone(subtag!("cator"))));

        let result = win_map.parse("GMT Standard Time", None);
        assert_eq!(result, Some(TimeZone(subtag!("gblon"))));
    }
}
