app/node_modules/markdown-it/lib/rules_block/reference.mjs

import { isSpace, normalizeReference } from '../common/utils.mjs'

export default function reference (state, startLine, _endLine, silent) {
  let pos = state.bMarks[startLine] + state.tShift[startLine]
  let max = state.eMarks[startLine]
  let nextLine = startLine + 1

  // if it's indented more than 3 spaces, it should be a code block
  if (state.sCount[startLine] - state.blkIndent >= 4) { return false }

  if (state.src.charCodeAt(pos) !== 0x5B/* [ */) { return false }

  function getNextLine (nextLine) {
    const endLine = state.lineMax

    if (nextLine >= endLine || state.isEmpty(nextLine)) {
      // empty line or end of input
      return null
    }

    let isContinuation = false

    // this would be a code block normally, but after paragraph
    // it's considered a lazy continuation regardless of what's there
    if (state.sCount[nextLine] - state.blkIndent > 3) { isContinuation = true }

    // quirk for blockquotes, this line should already be checked by that rule
    if (state.sCount[nextLine] < 0) { isContinuation = true }

    if (!isContinuation) {
      const terminatorRules = state.md.block.ruler.getRules('reference')
      const oldParentType = state.parentType
      state.parentType = 'reference'

      // Some tags can terminate paragraph without empty line.
      let terminate = false
      for (let i = 0, l = terminatorRules.length; i < l; i++) {
        if (terminatorRules[i](state, nextLine, endLine, true)) {
          terminate = true
          break
        }
      }

      state.parentType = oldParentType
      if (terminate) {
        // terminated by another block
        return null
      }
    }

    const pos = state.bMarks[nextLine] + state.tShift[nextLine]
    const max = state.eMarks[nextLine]

    // max + 1 explicitly includes the newline
    return state.src.slice(pos, max + 1)
  }

  let str = state.src.slice(pos, max + 1)

  max = str.length
  let labelEnd = -1

  for (pos = 1; pos < max; pos++) {
    const ch = str.charCodeAt(pos)
    if (ch === 0x5B /* [ */) {
      return false
    } else if (ch === 0x5D /* ] */) {
      labelEnd = pos
      break
    } else if (ch === 0x0A /* \n */) {
      const lineContent = getNextLine(nextLine)
      if (lineContent !== null) {
        str += lineContent
        max = str.length
        nextLine++
      }
    } else if (ch === 0x5C /* \ */) {
      pos++
      if (pos < max && str.charCodeAt(pos) === 0x0A) {
        const lineContent = getNextLine(nextLine)
        if (lineContent !== null) {
          str += lineContent
          max = str.length
          nextLine++
        }
      }
    }
  }

  if (labelEnd < 0 || str.charCodeAt(labelEnd + 1) !== 0x3A/* : */) { return false }

  // [label]:   destination   'title'
  //         ^^^ skip optional whitespace here
  for (pos = labelEnd + 2; pos < max; pos++) {
    const ch = str.charCodeAt(pos)
    if (ch === 0x0A) {
      const lineContent = getNextLine(nextLine)
      if (lineContent !== null) {
        str += lineContent
        max = str.length
        nextLine++
      }
    } else if (isSpace(ch)) {
      /* eslint no-empty:0 */
    } else {
      break
    }
  }

  // [label]:   destination   'title'
  //            ^^^^^^^^^^^ parse this
  const destRes = state.md.helpers.parseLinkDestination(str, pos, max)
  if (!destRes.ok) { return false }

  const href = state.md.normalizeLink(destRes.str)
  if (!state.md.validateLink(href)) { return false }

  pos = destRes.pos

  // save cursor state, we could require to rollback later
  const destEndPos = pos
  const destEndLineNo = nextLine

  // [label]:   destination   'title'
  //                       ^^^ skipping those spaces
  const start = pos
  for (; pos < max; pos++) {
    const ch = str.charCodeAt(pos)
    if (ch === 0x0A) {
      const lineContent = getNextLine(nextLine)
      if (lineContent !== null) {
        str += lineContent
        max = str.length
        nextLine++
      }
    } else if (isSpace(ch)) {
      /* eslint no-empty:0 */
    } else {
      break
    }
  }

  // [label]:   destination   'title'
  //                          ^^^^^^^ parse this
  let titleRes = state.md.helpers.parseLinkTitle(str, pos, max)
  while (titleRes.can_continue) {
    const lineContent = getNextLine(nextLine)
    if (lineContent === null) break
    str += lineContent
    pos = max
    max = str.length
    nextLine++
    titleRes = state.md.helpers.parseLinkTitle(str, pos, max, titleRes)
  }
  let title

  if (pos < max && start !== pos && titleRes.ok) {
    title = titleRes.str
    pos = titleRes.pos
  } else {
    title = ''
    pos = destEndPos
    nextLine = destEndLineNo
  }

  // skip trailing spaces until the rest of the line
  while (pos < max) {
    const ch = str.charCodeAt(pos)
    if (!isSpace(ch)) { break }
    pos++
  }

  if (pos < max && str.charCodeAt(pos) !== 0x0A) {
    if (title) {
      // garbage at the end of the line after title,
      // but it could still be a valid reference if we roll back
      title = ''
      pos = destEndPos
      nextLine = destEndLineNo
      while (pos < max) {
        const ch = str.charCodeAt(pos)
        if (!isSpace(ch)) { break }
        pos++
      }
    }
  }

  if (pos < max && str.charCodeAt(pos) !== 0x0A) {
    // garbage at the end of the line
    return false
  }

  const label = normalizeReference(str.slice(1, labelEnd))
  if (!label) {
    // CommonMark 0.20 disallows empty labels
    return false
  }

  // Reference can not terminate anything. This check is for safety only.
  /* istanbul ignore if */
  if (silent) { return true }

  if (typeof state.env.references === 'undefined') {
    state.env.references = {}
  }
  if (typeof state.env.references[label] === 'undefined') {
    state.env.references[label] = { title, href }
  }

  state.line = nextLine
  return true
}