index.mjs

import { eastAsianWidthType } from 'get-east-asian-width'

function is_surrogate (c1, c2) {
  return c1 >= 0xD800 && c1 <= 0xDBFF && c2 >= 0xDC00 && c2 <= 0xDFFF
}

function is_hangul (c) {
  // require('unicode-10.0.0/Script/Hangul/regex')
  /* eslint-disable max-len, no-misleading-character-class */
  return /[\u1100-\u11FF\u302E\u302F\u3131-\u318E\u3200-\u321E\u3260-\u327E\uA960-\uA97C\uAC00-\uD7A3\uD7B0-\uD7C6\uD7CB-\uD7FB\uFFA0-\uFFBE\uFFC2-\uFFC7\uFFCA-\uFFCF\uFFD2-\uFFD7\uFFDA-\uFFDC]/.test(c)
  /* eslint-enable max-len */
}

function process_inlines (tokens) {
  for (let i = 0; i < tokens.length; i++) {
    if (tokens[i].type !== 'softbreak') continue

    // default last/next character to space
    let last = ' '
    let next = ' '

    for (let j = i - 1; j >= 0; j--) {
      if (tokens[j].type !== 'text') continue

      const c1 = tokens[j].content.charCodeAt(tokens[j].content.length - 2)
      const c2 = tokens[j].content.charCodeAt(tokens[j].content.length - 1)

      last = tokens[j].content.slice(is_surrogate(c1, c2) ? -2 : -1)
      break
    }

    for (let j = i + 1; j < tokens.length; j++) {
      if (tokens[j].type !== 'text') continue

      const c1 = tokens[j].content.charCodeAt(0)
      const c2 = tokens[j].content.charCodeAt(1)

      next = tokens[j].content.slice(0, is_surrogate(c1, c2) ? 2 : 1)
      break
    }

    let remove_break = false

    // remove newline if it's adjacent to ZWSP
    if (last === '\u200b' || next === '\u200b') remove_break = true

    // remove newline if both characters are fullwidth (F), wide (W) or
    // halfwidth (H), but not Hangul
    if (/^[fwh]$/.test(eastAsianWidthType(last.codePointAt(0))[0]) &&
        /^[fwh]$/.test(eastAsianWidthType(next.codePointAt(0))[0])) {
      if (!is_hangul(last) && !is_hangul(next)) remove_break = true
    }

    if (remove_break) {
      tokens[i].type    = 'text'
      tokens[i].content = ''
    }
  }
}

function cjk_breaks (state) {
  for (let blkIdx = state.tokens.length - 1; blkIdx >= 0; blkIdx--) {
    if (state.tokens[blkIdx].type !== 'inline') continue

    process_inlines(state.tokens[blkIdx].children, state)
  }
}

export default function cjk_breaks_plugin (md) {
  md.core.ruler.push('cjk_breaks', cjk_breaks)
};