SEECBC/FrontEnd/util/markdown/plugin/markdown-it-katex.js

/* eslint-disable eqeqeq */
/* eslint-disable no-unused-vars */
/* eslint-disable @typescript-eslint/no-unused-vars */
/* eslint-disable prefer-const */
/* eslint-disable camelcase */
/* 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'

const katex = require('katex')

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

function math_inline(state, silent) {
  let 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) {
  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('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
}

module.exports = function math_plugin(md, options) {
  // Default options

  options = options || {}

  // set KaTeX as the renderer for markdown-it-simplemath
  const katexInline = function (latex) {
    options.displayMode = false
    try {
      return katex.renderToString(latex, options)
    } catch (error) {
      if (options.throwOnError) {
        // eslint-disable-next-line no-console
        console.log(error)
      }
      return latex
    }
  }

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

  const katexBlock = function (latex) {
    options.displayMode = true
    try {
      return '<p>' + katex.renderToString(latex, options) + '</p>'
    } catch (error) {
      if (options.throwOnError) {
        // eslint-disable-next-line no-console
        console.log(error)
      }
      return latex
    }
  }

  const 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
}