trait-kit 0.3.0

Module Standard Interface and Capability Management Center — A lightweight Rust library that provides a standard interface for module definition and Kit capability management.
Documentation 
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// Copyright (c) 2026 Kirky.X
// SPDX-License-Identifier: MIT
//! Implementation of [`I18nFormatter`] methods.

use std::cmp::Ordering;
use std::str::FromStr;

use icu::collator::Collator;
use icu::collator::options::CollatorOptions;
use icu::datetime::DateTimeFormatter;
use icu::datetime::fieldsets::YMD;
use icu::datetime::input::{Date, DateTime, Time};
use icu::decimal::DecimalFormatter;
use icu::decimal::input::Decimal;
use icu::decimal::options::DecimalFormatterOptions;
use icu::locale::Locale;
use icu::plurals::{PluralCategory, PluralRules, PluralRulesOptions};
use writeable::Writeable;

use super::{I18nError, I18nFormatter};

impl I18nFormatter {
    /// Create a new formatter for the given BCP-47 locale tag.
    ///
    /// # Errors
    /// Returns [`I18nError::InvalidLocale`] if the tag cannot be parsed,
    /// or [`I18nError::FormatError`] if ICU4X lacks compiled data for it.
    pub fn new(locale: &str) -> Result<Self, I18nError> {
        let parsed = Locale::from_str(locale).map_err(|e| I18nError::InvalidLocale {
            input: locale.to_string(),
            reason: e.to_string(),
        })?;

        let decimal_formatter =
            DecimalFormatter::try_new(parsed.clone().into(), DecimalFormatterOptions::default())
                .map_err(|e| I18nError::FormatError(e.to_string()))?;

        let plural_rules =
            PluralRules::try_new(parsed.clone().into(), PluralRulesOptions::default())
                .map_err(|e| I18nError::FormatError(e.to_string()))?;

        let collator = Collator::try_new(parsed.clone().into(), CollatorOptions::default())
            .map_err(|e| I18nError::FormatError(e.to_string()))?;

        Ok(Self {
            locale: parsed,
            decimal_formatter,
            plural_rules,
            collator,
        })
    }

    /// Format a floating-point number with locale-sensitive grouping
    /// and decimal separators.
    ///
    /// # Errors
    /// Returns [`I18nError::InvalidNumber`] for non-finite values or
    /// if the value cannot be parsed into a fixed decimal.
    pub fn format_number(&self, value: f64) -> Result<String, I18nError> {
        if !value.is_finite() {
            return Err(I18nError::InvalidNumber {
                input: value.to_string(),
                reason: "value is not finite (NaN or Infinity)".into(),
            });
        }
        let repr = format!("{value}");
        let decimal = Decimal::from_str(&repr).map_err(|e| I18nError::InvalidNumber {
            input: repr,
            reason: e.to_string(),
        })?;
        let formatted = self.decimal_formatter.format(&decimal);
        Ok(formatted.write_to_string().into_owned())
    }

    /// Format an ISO calendar date (year / month / day) using a medium
    /// length locale-specific pattern.
    ///
    /// # Errors
    /// Returns [`I18nError::DateError`] if any component is out of range,
    /// or [`I18nError::FormatError`] if the formatter cannot be constructed.
    pub fn format_date(&self, year: i32, month: u8, day: u8) -> Result<String, I18nError> {
        let date =
            Date::try_new_iso(year, month, day).map_err(|e| I18nError::DateError(e.to_string()))?;
        let time = Time::try_new(0, 0, 0, 0).map_err(|e| I18nError::DateError(e.to_string()))?;
        let datetime = DateTime { date, time };

        let dtf = DateTimeFormatter::try_new(self.locale.clone().into(), YMD::medium())
            .map_err(|e| I18nError::FormatError(e.to_string()))?;
        let formatted = dtf.format(&datetime);
        Ok(formatted.write_to_string().into_owned())
    }

    /// Return the plural category for `count` in the formatter's locale.
    ///
    /// # Errors
    /// This method does not currently fail, but returns `Result` for API
    /// consistency with the other formatting methods.
    pub fn plural_category(&self, count: u64) -> Result<PluralCategory, I18nError> {
        Ok(self.plural_rules.category_for(count))
    }

    /// Compare two strings using locale-sensitive collation rules.
    ///
    /// # Errors
    /// This method does not currently fail, but returns `Result` for API
    /// consistency with the other formatting methods.
    pub fn compare(&self, a: &str, b: &str) -> Result<Ordering, I18nError> {
        Ok(self.collator.compare(a, b))
    }
}