ultimate-vim/sources_non_forked/markdown-preview.nvim/app/pages/katex.js

// fork from https://github.com/waylonflinn/markdown-it-katex
/* Process inline math */
/*
Like markdown-it-simplemath, this is a stripped down, simplified version of:
https://github.com/runarberg/markdown-it-math
It differs in that it takes (a subset of) LaTeX as input and relies on KaTeX
for rendering output.
*/

/* jslint node: true */
'use strict'

// Test if potential opening or closing delimieter
// Assumes that there is a "$" at state.src[pos]
function isValidDelim (state, pos) {
  var prevChar; var nextChar

  var max = state.posMax

  var can_open = true

  var can_close = 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" */)) {
    can_close = false
  }
  if (nextChar === 0x20/* " " */ || nextChar === 0x09/* \t */) {
    can_open = false
  }

  return {
    can_open: can_open,
    can_close: can_close
  }
}

function math_inline (state, silent) {
  var start, match, token, res, pos, esc_count

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

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

  if (!silent) {
    token = state.push('math_inline', 'math', 0)
    token.markup = '$'
    token.content = state.src.slice(start, match)
  }

  state.pos = match + 1
  return true
}

function math_block (state, start, end, silent) {
  var firstLine; var lastLine; var next; var lastPos; var found = false; var token

  var pos = state.bMarks[start] + state.tShift[start]

  var 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('math_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
}

export default function math_plugin (md, options) {
  // Default options

  options = options || {}
  options.macros = options.macros || {}

  // set KaTeX as the renderer for markdown-it-simplemath
  var katexInline = function (latex) {
    const opt = {
      ...options
    }
    if (opt.displayMode === undefined) {
      opt.displayMode = false
    }
    try {
      return katex.renderToString(latex, opt)
    } catch (error) {
      if (opt.throwOnError) { console.log(error) }
      return latex
    }
  }

  var inlineRenderer = function (tokens, idx) {
    return katexInline(tokens[idx].content)
  }

  var katexBlock = function (latex) {
    const opt = {
      ...options
    }
    if (opt.displayMode === undefined) {
      opt.displayMode = true
    }
    try {
      return '<p>' + katex.renderToString(latex, opt) + '</p>'
    } catch (error) {
      if (opt.throwOnError) { console.log(error) }
      return latex
    }
  }

  var blockRenderer = function (tokens, idx) {
    return katexBlock(tokens[idx].content) + '\n'
  }

  md.inline.ruler.after('escape', 'math_inline', math_inline)
  md.block.ruler.after('blockquote', 'math_block', math_block, {
    alt: [ 'paragraph', 'reference', 'blockquote', 'list' ]
  })
  md.renderer.rules.math_inline = inlineRenderer
  md.renderer.rules.math_block = blockRenderer
}