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

// Block quotes

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

export default function blockquote (state, startLine, endLine, silent) {
  let pos = state.bMarks[startLine] + state.tShift[startLine]
  let max = state.eMarks[startLine]

  const oldLineMax = state.lineMax

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

  // check the block quote marker
  if (state.src.charCodeAt(pos) !== 0x3E/* > */) { return false }

  // we know that it's going to be a valid blockquote,
  // so no point trying to find the end of it in silent mode
  if (silent) { return true }

  const oldBMarks  = []
  const oldBSCount = []
  const oldSCount  = []
  const oldTShift  = []

  const terminatorRules = state.md.block.ruler.getRules('blockquote')

  const oldParentType = state.parentType
  state.parentType = 'blockquote'
  let lastLineEmpty = false
  let nextLine

  // Search the end of the block
  //
  // Block ends with either:
  //  1. an empty line outside:
  //     ```
  //     > test
  //
  //     ```
  //  2. an empty line inside:
  //     ```
  //     >
  //     test
  //     ```
  //  3. another tag:
  //     ```
  //     > test
  //      - - -
  //     ```
  for (nextLine = startLine; nextLine < endLine; nextLine++) {
    // check if it's outdented, i.e. it's inside list item and indented
    // less than said list item:
    //
    // ```
    // 1. anything
    //    > current blockquote
    // 2. checking this line
    // ```
    const isOutdented = state.sCount[nextLine] < state.blkIndent

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

    if (pos >= max) {
      // Case 1: line is not inside the blockquote, and this line is empty.
      break
    }

    if (state.src.charCodeAt(pos++) === 0x3E/* > */ && !isOutdented) {
      // This line is inside the blockquote.

      // set offset past spaces and ">"
      let initial = state.sCount[nextLine] + 1
      let spaceAfterMarker
      let adjustTab

      // skip one optional space after '>'
      if (state.src.charCodeAt(pos) === 0x20 /* space */) {
        // ' >   test '
        //     ^ -- position start of line here:
        pos++
        initial++
        adjustTab = false
        spaceAfterMarker = true
      } else if (state.src.charCodeAt(pos) === 0x09 /* tab */) {
        spaceAfterMarker = true

        if ((state.bsCount[nextLine] + initial) % 4 === 3) {
          // '  >\t  test '
          //       ^ -- position start of line here (tab has width===1)
          pos++
          initial++
          adjustTab = false
        } else {
          // ' >\t  test '
          //    ^ -- position start of line here + shift bsCount slightly
          //         to make extra space appear
          adjustTab = true
        }
      } else {
        spaceAfterMarker = false
      }

      let offset = initial
      oldBMarks.push(state.bMarks[nextLine])
      state.bMarks[nextLine] = pos

      while (pos < max) {
        const ch = state.src.charCodeAt(pos)

        if (isSpace(ch)) {
          if (ch === 0x09) {
            offset += 4 - (offset + state.bsCount[nextLine] + (adjustTab ? 1 : 0)) % 4
          } else {
            offset++
          }
        } else {
          break
        }

        pos++
      }

      lastLineEmpty = pos >= max

      oldBSCount.push(state.bsCount[nextLine])
      state.bsCount[nextLine] = state.sCount[nextLine] + 1 + (spaceAfterMarker ? 1 : 0)

      oldSCount.push(state.sCount[nextLine])
      state.sCount[nextLine] = offset - initial

      oldTShift.push(state.tShift[nextLine])
      state.tShift[nextLine] = pos - state.bMarks[nextLine]
      continue
    }

    // Case 2: line is not inside the blockquote, and the last line was empty.
    if (lastLineEmpty) { break }

    // Case 3: another tag found.
    let terminate = false
    for (let i = 0, l = terminatorRules.length; i < l; i++) {
      if (terminatorRules[i](state, nextLine, endLine, true)) {
        terminate = true
        break
      }
    }

    if (terminate) {
      // Quirk to enforce "hard termination mode" for paragraphs;
      // normally if you call `tokenize(state, startLine, nextLine)`,
      // paragraphs will look below nextLine for paragraph continuation,
      // but if blockquote is terminated by another tag, they shouldn't
      state.lineMax = nextLine

      if (state.blkIndent !== 0) {
        // state.blkIndent was non-zero, we now set it to zero,
        // so we need to re-calculate all offsets to appear as
        // if indent wasn't changed
        oldBMarks.push(state.bMarks[nextLine])
        oldBSCount.push(state.bsCount[nextLine])
        oldTShift.push(state.tShift[nextLine])
        oldSCount.push(state.sCount[nextLine])
        state.sCount[nextLine] -= state.blkIndent
      }

      break
    }

    oldBMarks.push(state.bMarks[nextLine])
    oldBSCount.push(state.bsCount[nextLine])
    oldTShift.push(state.tShift[nextLine])
    oldSCount.push(state.sCount[nextLine])

    // A negative indentation means that this is a paragraph continuation
    //
    state.sCount[nextLine] = -1
  }

  const oldIndent = state.blkIndent
  state.blkIndent = 0

  const token_o  = state.push('blockquote_open', 'blockquote', 1)
  token_o.markup = '>'
  const lines = [startLine, 0]
  token_o.map    = lines

  state.md.block.tokenize(state, startLine, nextLine)

  const token_c  = state.push('blockquote_close', 'blockquote', -1)
  token_c.markup = '>'

  state.lineMax = oldLineMax
  state.parentType = oldParentType
  lines[1] = state.line

  // Restore original tShift; this might not be necessary since the parser
  // has already been here, but just to make sure we can do that.
  for (let i = 0; i < oldTShift.length; i++) {
    state.bMarks[i + startLine] = oldBMarks[i]
    state.tShift[i + startLine] = oldTShift[i]
    state.sCount[i + startLine] = oldSCount[i]
    state.bsCount[i + startLine] = oldBSCount[i]
  }
  state.blkIndent = oldIndent

  return true
}