simple-email/node_modules/cardinal/examples/highlight-diff.js

'use strict'

var fs          =  require('fs')
var path        =  require('path')
var highlighter =  require('..')
var colors      =  require('ansicolors')
var diffFile    =  path.join(__dirname, 'git-diff.txt')
var diff        =  fs.readFileSync(diffFile, 'utf-8')

// @@ is not a valid js token, so when we see it, we can be sure that we are dealing with a git or svn diff
var diffRegex = /^@@[^@]+@@$/m
var diffIndRegex = /^(@@[^@]+@@)(.*)$/
var addRemRegex = /^[+-]/
var lines = diff.split('\n')

function isDiff(lines) {
  return !!lines
    .filter(function(line) {
      return diffRegex.test(line)
    })
    .length
}

diff = isDiff(lines)

function tryHighlight(code) {
  // TODO: need to remove symbols added to get valid code
  //       this should be done by getting the splits instead of the actual code from the highlighter
  //       now we can remove first / last one after highlighting completed
  function tryAppending(appended, tryNext) {
    try {
       return highlighter.highlight(code + appended)
    } catch (e) {
      return tryNext(code)
    }
  }

  function tryRemoveLeadingComma(tryNext) {
    var success
    try {
       success = highlighter.highlight(code.replace(/^( +),(.+)$/, '$1 $2'))
       return success
    } catch (e) {
      return tryNext(code)
    }
  }

  function tryPlain() {
    try {
      return highlighter.highlight(code)
    } catch (e) {
      return tryCloseMustache()
    }
  }

  function tryCloseMustache() { return tryAppending('}', tryCloseParen) }

  function tryCloseParen() { return tryAppending('\\)', tryCloseMustacheParen) }

  function tryCloseMustacheParen() { return tryAppending('})', tryRemovingCommas) }

  function tryRemovingCommas() { return tryRemoveLeadingComma(giveUp) }

  function giveUp() { return code }

  return tryPlain()
}

function highlightDiffInd(line, matches) {
  var highlighted = colors.brightBlue(matches[1])
  var code = matches[2]
  return code ? highlighted + tryHighlight(code) : highlighted
}

function colorsAddRemove(c) {
  return addRemRegex.test(c) ? colors.yellow(c) : c
}

function highlightDiff(line) {
  var diffIndMatches = diffIndRegex.exec(line)

  return diffIndMatches
    ? highlightDiffInd(line, diffIndMatches)
    : colorsAddRemove(line[0]) + tryHighlight(line.slice(1))
}

var highlightFn = diff ? highlightDiff : tryHighlight
var highlightedLines = lines.map(highlightFn)

console.log(highlightedLines.join('\n'))