postcss/lib/tokenize.es6

const SINGLE_QUOTE = '\''.charCodeAt(0)
const DOUBLE_QUOTE = '"'.charCodeAt(0)
const BACKSLASH = '\\'.charCodeAt(0)
const SLASH = '/'.charCodeAt(0)
const NEWLINE = '\n'.charCodeAt(0)
const SPACE = ' '.charCodeAt(0)
const FEED = '\f'.charCodeAt(0)
const TAB = '\t'.charCodeAt(0)
const CR = '\r'.charCodeAt(0)
const OPEN_SQUARE = '['.charCodeAt(0)
const CLOSE_SQUARE = ']'.charCodeAt(0)
const OPEN_PARENTHESES = '('.charCodeAt(0)
const CLOSE_PARENTHESES = ')'.charCodeAt(0)
const OPEN_CURLY = '{'.charCodeAt(0)
const CLOSE_CURLY = '}'.charCodeAt(0)
const SEMICOLON = ';'.charCodeAt(0)
const ASTERISK = '*'.charCodeAt(0)
const COLON = ':'.charCodeAt(0)
const AT = '@'.charCodeAt(0)

const RE_AT_END = /[ \n\t\r\f{}()'"\\;/[\]#]/g
const RE_WORD_END = /[ \n\t\r\f(){}:;@!'"\\\][#]|\/(?=\*)/g
const RE_BAD_BRACKET = /.[\\/("'\n]/
const RE_HEX_ESCAPE = /[a-f0-9]/i

export default function tokenizer (input, options = {}) {
  let css = input.css.valueOf()
  let ignore = options.ignoreErrors

  let code, next, quote, lines, last, content, escape
  let nextLine, nextOffset, escaped, escapePos, prev, n, currentToken

  let length = css.length
  let offset = -1
  let line = 1
  let pos = 0
  let buffer = []
  let returned = []

  function position () {
    return pos
  }

  function unclosed (what) {
    throw input.error('Unclosed ' + what, line, pos - offset)
  }

  function endOfFile () {
    return returned.length === 0 && pos >= length
  }

  function nextToken (opts) {
    if (returned.length) return returned.pop()
    if (pos >= length) return

    let ignoreUnclosed = opts ? opts.ignoreUnclosed : false

    code = css.charCodeAt(pos)
    if (
      code === NEWLINE || code === FEED ||
      (code === CR && css.charCodeAt(pos + 1) !== NEWLINE)
    ) {
      offset = pos
      line += 1
    }

    switch (code) {
      case NEWLINE:
      case SPACE:
      case TAB:
      case CR:
      case FEED:
        next = pos
        do {
          next += 1
          code = css.charCodeAt(next)
          if (code === NEWLINE) {
            offset = next
            line += 1
          }
        } while (
          code === SPACE ||
          code === NEWLINE ||
          code === TAB ||
          code === CR ||
          code === FEED
        )

        currentToken = ['space', css.slice(pos, next)]
        pos = next - 1
        break

      case OPEN_SQUARE:
      case CLOSE_SQUARE:
      case OPEN_CURLY:
      case CLOSE_CURLY:
      case COLON:
      case SEMICOLON:
      case CLOSE_PARENTHESES:
        let controlChar = String.fromCharCode(code)
        currentToken = [controlChar, controlChar, line, pos - offset]
        break

      case OPEN_PARENTHESES:
        prev = buffer.length ? buffer.pop()[1] : ''
        n = css.charCodeAt(pos + 1)
        if (
          prev === 'url' &&
          n !== SINGLE_QUOTE && n !== DOUBLE_QUOTE &&
          n !== SPACE && n !== NEWLINE && n !== TAB &&
          n !== FEED && n !== CR
        ) {
          next = pos
          do {
            escaped = false
            next = css.indexOf(')', next + 1)
            if (next === -1) {
              if (ignore || ignoreUnclosed) {
                next = pos
                break
              } else {
                unclosed('bracket')
              }
            }
            escapePos = next
            while (css.charCodeAt(escapePos - 1) === BACKSLASH) {
              escapePos -= 1
              escaped = !escaped
            }
          } while (escaped)

          currentToken = ['brackets', css.slice(pos, next + 1),
            line, pos - offset,
            line, next - offset
          ]

          pos = next
        } else {
          next = css.indexOf(')', pos + 1)
          content = css.slice(pos, next + 1)

          if (next === -1 || RE_BAD_BRACKET.test(content)) {
            currentToken = ['(', '(', line, pos - offset]
          } else {
            currentToken = ['brackets', content,
              line, pos - offset,
              line, next - offset
            ]
            pos = next
          }
        }

        break

      case SINGLE_QUOTE:
      case DOUBLE_QUOTE:
        quote = code === SINGLE_QUOTE ? '\'' : '"'
        next = pos
        do {
          escaped = false
          next = css.indexOf(quote, next + 1)
          if (next === -1) {
            if (ignore || ignoreUnclosed) {
              next = pos + 1
              break
            } else {
              unclosed('string')
            }
          }
          escapePos = next
          while (css.charCodeAt(escapePos - 1) === BACKSLASH) {
            escapePos -= 1
            escaped = !escaped
          }
        } while (escaped)

        content = css.slice(pos, next + 1)
        lines = content.split('\n')
        last = lines.length - 1

        if (last > 0) {
          nextLine = line + last
          nextOffset = next - lines[last].length
        } else {
          nextLine = line
          nextOffset = offset
        }

        currentToken = ['string', css.slice(pos, next + 1),
          line, pos - offset,
          nextLine, next - nextOffset
        ]

        offset = nextOffset
        line = nextLine
        pos = next
        break

      case AT:
        RE_AT_END.lastIndex = pos + 1
        RE_AT_END.test(css)
        if (RE_AT_END.lastIndex === 0) {
          next = css.length - 1
        } else {
          next = RE_AT_END.lastIndex - 2
        }

        currentToken = ['at-word', css.slice(pos, next + 1),
          line, pos - offset,
          line, next - offset
        ]

        pos = next
        break

      case BACKSLASH:
        next = pos
        escape = true
        while (css.charCodeAt(next + 1) === BACKSLASH) {
          next += 1
          escape = !escape
        }
        code = css.charCodeAt(next + 1)
        if (
          escape &&
          code !== SLASH &&
          code !== SPACE &&
          code !== NEWLINE &&
          code !== TAB &&
          code !== CR &&
          code !== FEED
        ) {
          next += 1
          if (RE_HEX_ESCAPE.test(css.charAt(next))) {
            while (RE_HEX_ESCAPE.test(css.charAt(next + 1))) {
              next += 1
            }
            if (css.charCodeAt(next + 1) === SPACE) {
              next += 1
            }
          }
        }

        currentToken = ['word', css.slice(pos, next + 1),
          line, pos - offset,
          line, next - offset
        ]

        pos = next
        break

      default:
        if (code === SLASH && css.charCodeAt(pos + 1) === ASTERISK) {
          next = css.indexOf('*/', pos + 2) + 1
          if (next === 0) {
            if (ignore || ignoreUnclosed) {
              next = css.length
            } else {
              unclosed('comment')
            }
          }

          content = css.slice(pos, next + 1)
          lines = content.split('\n')
          last = lines.length - 1

          if (last > 0) {
            nextLine = line + last
            nextOffset = next - lines[last].length
          } else {
            nextLine = line
            nextOffset = offset
          }

          currentToken = ['comment', content,
            line, pos - offset,
            nextLine, next - nextOffset
          ]

          offset = nextOffset
          line = nextLine
          pos = next
        } else {
          RE_WORD_END.lastIndex = pos + 1
          RE_WORD_END.test(css)
          if (RE_WORD_END.lastIndex === 0) {
            next = css.length - 1
          } else {
            next = RE_WORD_END.lastIndex - 2
          }

          currentToken = ['word', css.slice(pos, next + 1),
            line, pos - offset,
            line, next - offset
          ]

          buffer.push(currentToken)

          pos = next
        }

        break
    }

    pos++
    return currentToken
  }

  function back (token) {
    returned.push(token)
  }

  return {
    back,
    nextToken,
    endOfFile,
    position
  }
}