// 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 ).

use crate::ParseError;
use crate::extensions::unicode as unicode_ext;
use crate::parser::{
    ParserMode, SubtagIterator,
    parse_locale_with_single_variant_single_keyword_unicode_extension_from_iter,
};
use crate::preferences::{LocalePreferences, extensions::unicode::keywords::RegionalSubdivision};
use crate::subtags::{Language, Region, Script, Subtag, Variant};
use crate::{LanguageIdentifier, Locale};
use core::cmp::Ordering;
use core::default::Default;
use core::fmt;
use core::hash::Hash;
use core::str::FromStr;

/// A locale type optimized for use in fallbacking and the ICU4X data pipeline.
///
/// [`DataLocale`] contains less functionality than [`Locale`] but more than
/// [`LanguageIdentifier`] for better size and performance while still meeting
/// the needs of the ICU4X data pipeline.
///
/// In general, you should not need to construct one of these directly. If you do,
/// even though there is a direct `From<Locale>` conversion, you should
/// convert through the [`LocalePreferences`] type:
///
/// ```
/// use icu_locale_core::locale;
/// use icu_locale_core::preferences::LocalePreferences;
/// use icu_provider::DataLocale;
/// use writeable::assert_writeable_eq;
///
/// // Locale: American English with British user preferences
/// let locale = locale!("en-US-u-rg-gbzzzz");
///
/// // For language-priority fallback, the region override is ignored
/// let data_locale =
///     LocalePreferences::from(&locale).to_data_locale_language_priority();
/// assert_writeable_eq!(data_locale, "en-US");
///
/// // The direct conversion implicitly uses language-priority fallback
/// // (which is incorrect for some use cases).
/// assert_eq!(data_locale, DataLocale::from(&locale));
///
/// // For region-priority fallback, the region override is applied
/// let data_locale =
///     LocalePreferences::from(&locale).to_data_locale_region_priority();
/// assert_writeable_eq!(data_locale, "en-GB");
/// ```
///
/// [`DataLocale`] only supports `-u-sd` keywords, to reflect the current state of CLDR data
/// lookup and fallback. This may change in the future.
///
/// ```
/// use icu_locale_core::{locale, Locale};
/// use icu_provider::DataLocale;
///
/// let locale = "hi-IN-t-en-h0-hybrid-u-attr-ca-buddhist-sd-inas"
///     .parse::<Locale>()
///     .unwrap();
///
/// assert_eq!(
///     DataLocale::from(locale),
///     DataLocale::from(locale!("hi-IN-u-sd-inas"))
/// );
/// ```
///
/// [`LocalePreferences`]: crate::preferences::LocalePreferences
#[derive(Clone, Copy)]
#[non_exhaustive]
pub struct DataLocale {
    /// Language subtag
    pub language: Language,
    /// Script subtag
    pub script: Option<Script>,
    /// Region subtag
    pub region: Option<Region>,
    /// Variant subtag
    pub variant: Option<Variant>,
    /// Subivision (-u-sd-) subtag
    // TODO(3.0): Use `SubdivisionSuffix` type
    pub subdivision: Option<Subtag>,
}

impl PartialEq for DataLocale {
    fn eq(&self, other: &Self) -> bool {
        self.as_tuple() == other.as_tuple()
    }
}

impl Eq for DataLocale {}

impl Hash for DataLocale {
    fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
        self.as_tuple().hash(state);
    }
}

impl Default for DataLocale {
    fn default() -> Self {
        Self {
            language: Language::UNKNOWN,
            script: None,
            region: None,
            variant: None,
            subdivision: None,
        }
    }
}

impl DataLocale {
    /// `const` version of `Default::default`
    pub const fn default() -> Self {
        DataLocale {
            language: Language::UNKNOWN,
            script: None,
            region: None,
            variant: None,
            subdivision: None,
        }
    }
}

impl Default for &DataLocale {
    fn default() -> Self {
        static DEFAULT: DataLocale = DataLocale::default();
        &DEFAULT
    }
}

impl fmt::Debug for DataLocale {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "DataLocale{{{self}}}")
    }
}

impl_writeable_for_each_subtag_str_no_test!(DataLocale, selff, selff.script.is_none() && selff.region.is_none() && selff.variant.is_none() && selff.subdivision.is_none() => Some(selff.language.as_str()));

impl From<LanguageIdentifier> for DataLocale {
    fn from(langid: LanguageIdentifier) -> Self {
        Self::from(&langid)
    }
}

impl From<Locale> for DataLocale {
    fn from(locale: Locale) -> Self {
        Self::from(&locale)
    }
}

impl From<&LanguageIdentifier> for DataLocale {
    fn from(langid: &LanguageIdentifier) -> Self {
        Self {
            language: langid.language,
            script: langid.script,
            region: langid.region,
            variant: langid.variants.iter().copied().next(),
            subdivision: None,
        }
    }
}

impl From<&Locale> for DataLocale {
    fn from(locale: &Locale) -> Self {
        LocalePreferences::from(locale).to_data_locale_language_priority()
    }
}

impl From<(Language, Option<Script>, Option<Region>)> for DataLocale {
    fn from((l, s, r): (Language, Option<Script>, Option<Region>)) -> Self {
        Self::from_parts(
            l,
            s,
            r.map(|r| unicode_ext::SubdivisionId::new(r, unicode_ext::SubdivisionSuffix::UNKNOWN)),
            None,
        )
    }
}

impl FromStr for DataLocale {
    type Err = ParseError;
    #[inline]
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Self::try_from_str(s)
    }
}

impl DataLocale {
    #[inline]
    /// Parses a [`DataLocale`].
    pub const fn try_from_str(s: &str) -> Result<Self, ParseError> {
        Self::try_from_utf8(s.as_bytes())
    }

    /// Parses a [`DataLocale`] from a UTF-8 byte slice.
    pub const fn try_from_utf8(code_units: &[u8]) -> Result<Self, ParseError> {
        let (language, script, region, variant, keyword) =
            match parse_locale_with_single_variant_single_keyword_unicode_extension_from_iter(
                SubtagIterator::new(code_units),
                ParserMode::Locale,
            ) {
                Ok(o) => o,
                Err(e) => return Err(e),
            };

        let subdivision = if let Some((key, value)) = keyword {
            if let Some(value) = value
                && let RegionalSubdivision::UNICODE_EXTENSION_KEY = key
            {
                let Ok(subdivision) = unicode_ext::SubdivisionId::try_from_subtag(value) else {
                    return Err(ParseError::InvalidExtension);
                };
                if let Some(region) = region
                    && (region.into_raw()[0] != subdivision.region.into_raw()[0]
                        || region.into_raw()[1] != subdivision.region.into_raw()[1]
                        || region.into_raw()[2] != subdivision.region.into_raw()[2])
                {
                    Some(unicode_ext::SubdivisionId::new(
                        region,
                        unicode_ext::SubdivisionSuffix::UNKNOWN,
                    ))
                } else {
                    Some(subdivision)
                }
            } else {
                return Err(ParseError::InvalidExtension);
            }
        } else if let Some(region) = region {
            Some(unicode_ext::SubdivisionId::new(
                region,
                unicode_ext::SubdivisionSuffix::UNKNOWN,
            ))
        } else {
            None
        };

        Ok(Self::from_parts(language, script, subdivision, variant))
    }

    pub(crate) fn for_each_subtag_str<E, F>(&self, f: &mut F) -> Result<(), E>
    where
        F: FnMut(&str) -> Result<(), E>,
    {
        f(self.language.as_str())?;
        if let Some(ref script) = self.script {
            f(script.as_str())?;
        }
        if let Some(ref region) = self.region {
            f(region.as_str())?;
        }
        if let Some(ref single_variant) = self.variant {
            f(single_variant.as_str())?;
        }
        if let Some(extensions) = self.extensions() {
            extensions.for_each_subtag_str(f)?;
        }
        Ok(())
    }

    fn region_and_subdivision(&self) -> Option<unicode_ext::SubdivisionId> {
        self.subdivision
            .and_then(|s| unicode_ext::SubdivisionId::try_from_str(s.as_str()).ok())
            .or_else(|| {
                self.region.map(|region| unicode_ext::SubdivisionId {
                    region,
                    suffix: unicode_ext::SubdivisionSuffix::UNKNOWN,
                })
            })
    }

    fn as_tuple(
        &self,
    ) -> (
        Language,
        Option<Script>,
        Option<unicode_ext::SubdivisionId>,
        Option<Variant>,
    ) {
        (
            self.language,
            self.script,
            self.region_and_subdivision(),
            self.variant,
        )
    }

    pub(crate) const fn from_parts(
        language: Language,
        script: Option<Script>,
        region: Option<unicode_ext::SubdivisionId>,
        variant: Option<Variant>,
    ) -> Self {
        Self {
            language,
            script,
            region: if let Some(r) = region {
                Some(r.region)
            } else {
                None
            },
            variant,
            subdivision: if let Some(r) = region {
                Some(r.into_subtag())
            } else {
                None
            },
        }
    }

    /// Returns an ordering suitable for use in [`BTreeSet`].
    ///
    /// [`BTreeSet`]: alloc::collections::BTreeSet
    pub fn total_cmp(&self, other: &Self) -> Ordering {
        self.as_tuple().cmp(&other.as_tuple())
    }

    /// Compare this [`DataLocale`] with BCP-47 bytes.
    ///
    /// The return value is equivalent to what would happen if you first converted this
    /// [`DataLocale`] to a BCP-47 string and then performed a byte comparison.
    ///
    /// This function is case-sensitive and results in a *total order*, so it is appropriate for
    /// binary search. The only argument producing [`Ordering::Equal`] is `self.to_string()`.
    ///
    /// # Examples
    ///
    /// ```
    /// use core::cmp::Ordering;
    /// use icu_provider::DataLocale;
    ///
    /// let bcp47_strings: &[&str] = &[
    ///     "ca",
    ///     "ca-ES",
    ///     "ca-ES-u-sd-esct",
    ///     "ca-ES-valencia",
    ///     "cat",
    ///     "pl-Latn-PL",
    ///     "und",
    ///     "und-fonipa",
    ///     "zh",
    /// ];
    ///
    /// for ab in bcp47_strings.windows(2) {
    ///     let a = ab[0];
    ///     let b = ab[1];
    ///     assert_eq!(a.cmp(b), Ordering::Less, "strings: {} < {}", a, b);
    ///     let a_loc: DataLocale = a.parse().unwrap();
    ///     assert_eq!(
    ///         a_loc.strict_cmp(a.as_bytes()),
    ///         Ordering::Equal,
    ///         "strict_cmp: {} == {}",
    ///         a_loc,
    ///         a
    ///     );
    ///     assert_eq!(
    ///         a_loc.strict_cmp(b.as_bytes()),
    ///         Ordering::Less,
    ///         "strict_cmp: {} < {}",
    ///         a_loc,
    ///         b
    ///     );
    ///     let b_loc: DataLocale = b.parse().unwrap();
    ///     assert_eq!(
    ///         b_loc.strict_cmp(b.as_bytes()),
    ///         Ordering::Equal,
    ///         "strict_cmp: {} == {}",
    ///         b_loc,
    ///         b
    ///     );
    ///     assert_eq!(
    ///         b_loc.strict_cmp(a.as_bytes()),
    ///         Ordering::Greater,
    ///         "strict_cmp: {} > {}",
    ///         b_loc,
    ///         a
    ///     );
    /// }
    /// ```
    ///
    /// Comparison against invalid strings:
    ///
    /// ```
    /// use icu_provider::DataLocale;
    ///
    /// let invalid_strings: &[&str] = &[
    ///     // Less than "ca-ES"
    ///     "CA",
    ///     "ar-x-gbp-FOO",
    ///     // Greater than "ca-AR"
    ///     "ca_ES",
    ///     "ca-ES-x-gbp-FOO",
    /// ];
    ///
    /// let data_locale = "ca-ES".parse::<DataLocale>().unwrap();
    ///
    /// for s in invalid_strings.iter() {
    ///     let expected_ordering = "ca-AR".cmp(s);
    ///     let actual_ordering = data_locale.strict_cmp(s.as_bytes());
    ///     assert_eq!(expected_ordering, actual_ordering, "{}", s);
    /// }
    /// ```
    pub fn strict_cmp(&self, other: &[u8]) -> Ordering {
        writeable::cmp_utf8(self, other)
    }

    /// Returns whether this [`DataLocale`] is `und` in the locale and extensions portion.
    ///
    /// # Examples
    ///
    /// ```
    /// use icu_provider::DataLocale;
    ///
    /// assert!("und".parse::<DataLocale>().unwrap().is_unknown());
    /// assert!(!"de-u-sd-denw".parse::<DataLocale>().unwrap().is_unknown());
    /// assert!(!"und-ES".parse::<DataLocale>().unwrap().is_unknown());
    /// ```
    pub fn is_unknown(&self) -> bool {
        self.language.is_unknown()
            && self.script.is_none()
            && self.region.is_none()
            && self.variant.is_none()
            && self.subdivision.is_none()
    }

    /// Converts this `DataLocale` into a [`Locale`].
    pub fn into_locale(self) -> Locale {
        Locale {
            id: LanguageIdentifier {
                language: self.language,
                script: self.script,
                region: self.region,
                variants: self
                    .variant
                    .map(crate::subtags::Variants::from_variant)
                    .unwrap_or_default(),
            },
            extensions: self.extensions().unwrap_or_default(),
        }
    }

    fn extensions(&self) -> Option<crate::extensions::Extensions> {
        Some(crate::extensions::Extensions {
            unicode: unicode_ext::Unicode {
                keywords: unicode_ext::Keywords::new_single(
                    RegionalSubdivision::UNICODE_EXTENSION_KEY,
                    RegionalSubdivision(
                        self.region_and_subdivision()
                            .filter(|sd| !sd.suffix.is_unknown())?,
                    )
                    .into(),
                ),
                ..Default::default()
            },
            ..Default::default()
        })
    }
}

#[test]
fn test_data_locale_to_string() {
    struct TestCase {
        pub locale: &'static str,
        pub expected: &'static str,
    }

    for cas in [
        TestCase {
            locale: "und",
            expected: "und",
        },
        TestCase {
            locale: "und-u-sd-sdd",
            expected: "und-SD-u-sd-sdd",
        },
        TestCase {
            locale: "en-ZA-u-sd-zaa",
            expected: "en-ZA-u-sd-zaa",
        },
        TestCase {
            locale: "en-ZA-u-sd-sdd",
            expected: "en-ZA",
        },
    ] {
        let locale = cas.locale.parse::<DataLocale>().unwrap();
        writeable::assert_writeable_eq!(locale, cas.expected);
    }
}

#[test]
fn test_data_locale_from_string() {
    #[derive(Debug)]
    struct TestCase {
        pub input: &'static str,
        pub success: bool,
    }

    for cas in [
        TestCase {
            input: "und",
            success: true,
        },
        TestCase {
            input: "und-u-cu-gbp",
            success: false,
        },
        TestCase {
            input: "en-ZA-u-sd-zaa",
            success: true,
        },
        TestCase {
            input: "en...",
            success: false,
        },
    ] {
        let data_locale = match (DataLocale::from_str(cas.input), cas.success) {
            (Ok(l), true) => l,
            (Err(_), false) => {
                continue;
            }
            (Ok(_), false) => {
                panic!("DataLocale parsed but it was supposed to fail: {cas:?}");
            }
            (Err(_), true) => {
                panic!("DataLocale was supposed to parse but it failed: {cas:?}");
            }
        };
        writeable::assert_writeable_eq!(data_locale, cas.input);
    }
}
