intl.ts

Full source

/**
 * Shared Intl object instances with lazy initialization.
 *
 * Intl constructors are expensive (~0.05-0.1ms each), so we cache instances
 * for reuse across the codebase instead of creating new ones each time.
 * Lazy initialization ensures we only pay the cost when actually needed.
 */

// Segmenters for Unicode text processing (lazily initialized)
let graphemeSegmenter: Intl.Segmenter | null = null
let wordSegmenter: Intl.Segmenter | null = null

export function getGraphemeSegmenter(): Intl.Segmenter {
  if (!graphemeSegmenter) {
    graphemeSegmenter = new Intl.Segmenter(undefined, {
      granularity: 'grapheme',
    })
  }
  return graphemeSegmenter
}

/**
 * Extract the first grapheme cluster from a string.
 * Returns '' for empty strings.
 */
export function firstGrapheme(text: string): string {
  if (!text) return ''
  const segments = getGraphemeSegmenter().segment(text)
  const first = segments[Symbol.iterator]().next().value
  return first?.segment ?? ''
}

/**
 * Extract the last grapheme cluster from a string.
 * Returns '' for empty strings.
 */
export function lastGrapheme(text: string): string {
  if (!text) return ''
  let last = ''
  for (const { segment } of getGraphemeSegmenter().segment(text)) {
    last = segment
  }
  return last
}

export function getWordSegmenter(): Intl.Segmenter {
  if (!wordSegmenter) {
    wordSegmenter = new Intl.Segmenter(undefined, { granularity: 'word' })
  }
  return wordSegmenter
}

// RelativeTimeFormat cache (keyed by style:numeric)
const rtfCache = new Map<string, Intl.RelativeTimeFormat>()

export function getRelativeTimeFormat(
  style: 'long' | 'short' | 'narrow',
  numeric: 'always' | 'auto',
): Intl.RelativeTimeFormat {
  const key = `${style}:${numeric}`
  let rtf = rtfCache.get(key)
  if (!rtf) {
    rtf = new Intl.RelativeTimeFormat('en', { style, numeric })
    rtfCache.set(key, rtf)
  }
  return rtf
}

// Timezone is constant for the process lifetime
let cachedTimeZone: string | null = null

export function getTimeZone(): string {
  if (!cachedTimeZone) {
    cachedTimeZone = Intl.DateTimeFormat().resolvedOptions().timeZone
  }
  return cachedTimeZone
}

// System locale language subtag (e.g. 'en', 'ja') is constant for the process
// lifetime. null = not yet computed; undefined = computed but unavailable (so
// a stripped-ICU environment fails once instead of retrying on every call).
let cachedSystemLocaleLanguage: string | undefined | null = null

export function getSystemLocaleLanguage(): string | undefined {
  if (cachedSystemLocaleLanguage === null) {
    try {
      const locale = Intl.DateTimeFormat().resolvedOptions().locale
      cachedSystemLocaleLanguage = new Intl.Locale(locale).language
    } catch {
      cachedSystemLocaleLanguage = undefined
    }
  }
  return cachedSystemLocaleLanguage
}