wiki/client/components/editor/common/katex.js

// Test if potential opening or closing delimieter
// Assumes that there is a "$" at state.src[pos]
function isValidDelim (state, pos) {
  let prevChar
  let nextChar
  let max = state.posMax
  let canOpen = true
  let canClose = true

  prevChar = pos > 0 ? state.src.charCodeAt(pos - 1) : -1
  nextChar = pos + 1 <= max ? state.src.charCodeAt(pos + 1) : -1

  // Check non-whitespace conditions for opening and closing, and
  // check that closing delimeter isn't followed by a number
  if (prevChar === 0x20/* " " */ || prevChar === 0x09/* \t */ ||
          (nextChar >= 0x30/* "0" */ && nextChar <= 0x39/* "9" */)) {
    canClose = false
  }
  if (nextChar === 0x20/* " " */ || nextChar === 0x09/* \t */) {
    canOpen = false
  }

  return {
    canOpen: canOpen,
    canClose: canClose
  }
}

export default {
  katexInline (state, silent) {
    let start, match, token, res, pos

    if (state.src[state.pos] !== '$') { return false }

    res = isValidDelim(state, state.pos)
    if (!res.canOpen) {
      if (!silent) { state.pending += '$' }
      state.pos += 1
      return true
    }

    // First check for and bypass all properly escaped delimieters
    // This loop will assume that the first leading backtick can not
    // be the first character in state.src, which is known since
    // we have found an opening delimieter already.
    start = state.pos + 1
    match = start
    while ((match = state.src.indexOf('$', match)) !== -1) {
      // Found potential $, look for escapes, pos will point to
      // first non escape when complete
      pos = match - 1
      while (state.src[pos] === '\\') { pos -= 1 }

      // Even number of escapes, potential closing delimiter found
      if (((match - pos) % 2) === 1) { break }
      match += 1
    }

    // No closing delimter found.  Consume $ and continue.
    if (match === -1) {
      if (!silent) { state.pending += '$' }
      state.pos = start
      return true
    }

    // Check if we have empty content, ie: $$.  Do not parse.
    if (match - start === 0) {
      if (!silent) { state.pending += '$$' }
      state.pos = start + 1
      return true
    }

    // Check for valid closing delimiter
    res = isValidDelim(state, match)
    if (!res.canClose) {
      if (!silent) { state.pending += '$' }
      state.pos = start
      return true
    }

    if (!silent) {
      token = state.push('katex_inline', 'math', 0)
      token.markup = '$'
      token.content = state.src
        // Extract the math part without the $
        .slice(start, match)
        // Escape the curly braces since they will be interpreted as
        // attributes by markdown-it-attrs (the "curly_attributes"
        // core rule)
        .replaceAll("{", "{{")
        .replaceAll("}", "}}")
    }

    state.pos = match + 1
    return true
  },

  katexBlock (state, start, end, silent) {
    let firstLine; let lastLine; let next; let lastPos; let found = false; let token
    let pos = state.bMarks[start] + state.tShift[start]
    let max = state.eMarks[start]

    if (pos + 2 > max) { return false }
    if (state.src.slice(pos, pos + 2) !== '$$') { return false }

    pos += 2
    firstLine = state.src.slice(pos, max)

    if (silent) { return true }
    if (firstLine.trim().slice(-2) === '$$') {
      // Single line expression
      firstLine = firstLine.trim().slice(0, -2)
      found = true
    }

    for (next = start; !found;) {
      next++

      if (next >= end) { break }

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

      if (pos < max && state.tShift[next] < state.blkIndent) {
        // non-empty line with negative indent should stop the list:
        break
      }

      if (state.src.slice(pos, max).trim().slice(-2) === '$$') {
        lastPos = state.src.slice(0, max).lastIndexOf('$$')
        lastLine = state.src.slice(pos, lastPos)
        found = true
      }
    }

    state.line = next + 1

    token = state.push('katex_block', 'math', 0)
    token.block = true
    token.content = (firstLine && firstLine.trim() ? firstLine + '\n' : '') +
    state.getLines(start + 1, next, state.tShift[start], true) +
    (lastLine && lastLine.trim() ? lastLine : '')
    token.map = [ start, state.line ]
    token.markup = '$$'
    return true
  }
}