index.js

export default function parse (markdown = '') {
  // TODO: Add input checking

  const states = {
    blankline: 1,
    code: 2
  }

  const tags = {
    code: {
      open: '<pre><code>',
      close: '</code></pre>'
    }
  }

  let state = states.blankline
  let spaces = 0
  const ctx = Object.create(null)
  ctx.value = ''
  ctx.output = ''

  const lexer = /\t|\s|\n|\r|[^\t\n\r]+/y
  const output = () => {
    ctx.output += ctx.value
    ctx.value = ''
  }
  let tokens = []
  let match = ''
  let end = false
  while ((tokens = lexer.exec(markdown)) !== null) {
    match = tokens[0]
    end = lexer.lastIndex === markdown.length

    if (state === states.blankline) {
      switch (match) {
        case '\t':
          spaces += 4
          continue
        case ' ':
          spaces += 1
          continue
        default:
          if (spaces >= 4) {
            state = states.code
            spaces = 0
          }
          break
      }
    }

    if (state === states.code) {
      if (ctx.value === '') { ctx.value += tags.code.open }
      if (/\n|\r/.test(match)) {
        ctx.value += '\n'
        state = states.blankline
        continue
      }
      ctx.value += match
      if (end) {
        ctx.value += '\n' + tags.code.close
        output()
      }
    }
  }
  // // flush the last value
  // if (ctx.entry.length !== 0) {
  //   this.valueEnd(ctx);
  //   this.entryEnd(ctx);
  // }

  return ctx.output
}