import { useEffect, useState } from 'react'

import { loadSegmenter, type Segmenter } from '../lib/segment'

// Loads the Chinese word list, once per session, and only for a writer who is
// going to use it.
//
// Modelled on useSpellChecker, and gated harder. That hook loads for everyone,
// because everyone's English gets spell-checked; this one loads a megabyte for
// the one direction that needs it, and an account practising English would
// never ask a single question of it. The gate is the writer's own setting rather
// than a guess from their text: a Mandarin native drafting English quotes
// Chinese in it constantly, and none of that is what this is for.
//
// A failure resolves to null, which every consumer already handles as "no
// segmentation" — the Chinese hover quietly does nothing rather than the editor
// refusing to open.
export function useSegmenter(enabled: boolean): Segmenter | null {
  const [segmenter, setSegmenter] = useState<Segmenter | null>(null)

  useEffect(() => {
    if (!enabled) {
      // Turning the direction back drops it. It is a megabyte of resident map
      // whose only consumer just switched off, and re-loading costs one fetch
      // that the browser cache answers.
      setSegmenter(null)
      return
    }
    let cancelled = false
    loadSegmenter().then((seg) => {
      if (!cancelled) setSegmenter(seg)
    })
    return () => {
      cancelled = true
    }
  }, [enabled])

  return segmenter
}