path: root/src/css/cssparser.nim

import std/options

import html/domexception
import types/opt
import utils/twtstr

type
  CSSTokenType* = enum
    cttIdent, cttFunction, cttAtKeyword, cttHash, cttString,
    cttBadString, cttUrl, cttBadUrl, cttDelim, cttNumber, cttINumber,
    cttPercentage, cttDimension, cttIDimension, cttWhitespace, cttCdo,
    cttCdc, cttColon, cttSemicolon, cttComma, cttRbracket, cttLbracket,
    cttLparen, cttRparen, cttLbrace, cttRbrace

  CSSTokenizerState = object
    at: int
    buf: string

  CSSParseState = object
    tokens: seq[CSSComponentValue]
    at: int

  tflaga = enum
    tflagaUnrestricted, tflagaId

  CSSComponentValue* = ref object of RootObj

  CSSToken* = ref object of CSSComponentValue
    case t*: CSSTokenType
    of cttIdent, cttFunction, cttAtKeyword, cttHash, cttString, cttUrl:
      tflaga*: tflaga
      value*: string
    of cttDelim:
      cvalue*: char
    of cttNumber, cttINumber, cttPercentage, cttDimension, cttIDimension:
      nvalue*: float32
      unit*: string
    else: discard

  CSSRule* = ref object of CSSComponentValue
    prelude*: seq[CSSComponentValue]
    oblock*: CSSSimpleBlock

  CSSAtRule* = ref object of CSSRule
    name*: string

  CSSQualifiedRule* = ref object of CSSRule

  CSSDeclaration* = ref object of CSSComponentValue
    name*: string
    value*: seq[CSSComponentValue]
    important*: bool

  CSSFunctionType* = enum
    cftUnknown = "-cha-unknown"
    cftNot = "not"
    cftIs = "is"
    cftWhere = "where"
    cftNthChild = "nth-child"
    cftNthLastChild = "nth-last-child"
    cftLang = "lang"
    cftRgb = "rgb"
    cftRgba = "rgba"
    cftChaAnsi = "-cha-ansi"
    cftUrl = "url"
    cftSrc = "src"
    cftVar = "var"
    cftHsl = "hsl"
    cftHsla = "hsla"
    cftCalc = "calc"
    cftCounter = "counter"

  CSSFunction* = ref object of CSSComponentValue
    name*: CSSFunctionType
    value*: seq[CSSComponentValue]

  CSSSimpleBlock* = ref object of CSSComponentValue
    token*: CSSToken
    value*: seq[CSSComponentValue]

  CSSRawStylesheet* = object
    value*: seq[CSSRule]

  CSSAnB* = tuple[A, B: int32]

# For debugging
proc `$`*(c: CSSComponentValue): string =
  result = ""
  if c of CSSToken:
    let c = CSSToken(c)
    case c.t:
    of cttFunction, cttAtKeyword:
      result &= $c.t & c.value & '\n'
    of cttUrl:
      result &= "url(" & c.value & ")"
    of cttHash:
      result &= '#' & c.value
    of cttIdent:
      result &= c.value
    of cttString:
      result &= ("\"" & c.value & "\"")
    of cttDelim:
      if c.cvalue != char(128):
        result &= c.cvalue
      else:
        result &= "<UNICODE>"
    of cttDimension, cttNumber:
      result &= $c.nvalue & c.unit
    of cttINumber, cttIDimension:
      result &= $int32(c.nvalue) & c.unit
    of cttPercentage:
      result &= $c.nvalue & "%"
    of cttColon:
      result &= ":"
    of cttWhitespace:
      result &= " "
    of cttSemicolon:
      result &= ";\n"
    of cttComma:
      result &= ","
    else:
      result &= $c.t & '\n'
  elif c of CSSDeclaration:
    let decl = CSSDeclaration(c)
    result &= decl.name
    result &= ": "
    for s in decl.value:
      result &= $s
    if decl.important:
      result &= " !important"
    result &= ";"
  elif c of CSSFunction:
    result &= $CSSFunction(c).name & "("
    for s in CSSFunction(c).value:
      result &= $s
    result &= ")"
  elif c of CSSSimpleBlock:
    case CSSSimpleBlock(c).token.t
    of cttLbrace: result &= "{\n"
    of cttLparen: result &= "("
    of cttLbracket: result &= "["
    else: discard
    for s in CSSSimpleBlock(c).value:
      result &= $s
    case CSSSimpleBlock(c).token.t
    of cttLbrace: result &= "\n}"
    of cttLparen: result &= ")"
    of cttLbracket: result &= "]"
    else: discard
  elif c of CSSRule:
    if c of CSSAtRule:
      result &= CSSAtRule(c).name & " "
    result &= $CSSRule(c).prelude & "\n"
    result &= $CSSRule(c).oblock

func `==`*(a: CSSComponentValue; b: CSSTokenType): bool =
  return a of CSSToken and CSSToken(a).t == b

const IdentStart = AsciiAlpha + NonAscii + {'_'}
const Ident = IdentStart + AsciiDigit + {'-'}

proc consume(state: var CSSTokenizerState): char =
  let c = state.buf[state.at]
  inc state.at
  return c

proc seek(state: var CSSTokenizerState; n: int) =
  state.at += n

proc consumeRChar(state: var CSSTokenizerState): char =
  let u = state.buf.nextUTF8(state.at)
  if u < 0x80:
    return char(u)
  return char(128)

proc reconsume(state: var CSSTokenizerState) =
  dec state.at

func peek(state: CSSTokenizerState; i: int = 0): char =
  return state.buf[state.at + i]

func has(state: CSSTokenizerState; i: int = 0): bool =
  return state.at + i < state.buf.len

# next, next(1)
proc startsWithIdentSequenceDash(state: var CSSTokenizerState): bool =
  return state.has() and state.peek() in IdentStart + {'-'} or
    state.has(1) and state.peek() == '\\' and state.peek(1) != '\n'

# next, next(1), next(2)
proc startsWithIdentSequence(state: var CSSTokenizerState): bool =
  if not state.has():
    return false
  case state.peek()
  of '-':
    return state.has(1) and state.peek(1) in IdentStart + {'-'} or
      state.has(2) and state.peek(1) == '\\' and state.peek(2) != '\n'
  of IdentStart:
    return true
  of '\\':
    return state.has(1) and state.peek(1) != '\n'
  else:
    return false

proc skipWhitespace(state: var CSSTokenizerState) =
  while state.has() and state.peek() in AsciiWhitespace:
    state.seek(1)

proc consumeEscape(state: var CSSTokenizerState): string =
  if not state.has():
    return "\uFFFD"
  let c = state.consume()
  if c in AsciiHexDigit:
    var num = uint32(hexValue(c))
    var i = 0
    while i <= 5 and state.has():
      let c = state.consume()
      if hexValue(c) == -1:
        state.reconsume()
        break
      num *= 0x10
      num += uint32(hexValue(c))
      inc i
    if state.has() and state.peek() in AsciiWhitespace:
      state.seek(1)
    if num == 0 or num > 0x10FFFF or num in 0xD800u32..0xDFFFu32:
      return "\uFFFD"
    else:
      return num.toUTF8()
  else:
    return $c #NOTE this assumes the caller doesn't care about non-ascii

proc consumeString(state: var CSSTokenizerState; ending: char): CSSToken =
  var s = ""
  while state.has():
    let c = state.consume()
    case c
    of '\n':
      state.reconsume()
      return CSSToken(t: cttBadString)
    of '\\':
      if not state.has():
        continue
      elif state.peek() == '\n':
        state.seek(1)
      else:
        s &= consumeEscape(state)
    elif c == ending:
      break
    else:
      s &= c
  return CSSToken(t: cttString, value: s)

proc consumeIdentSequence(state: var CSSTokenizerState): string =
  var s = ""
  while state.has():
    let c = state.consume()
    if c == '\\' and state.has() and state.peek() != '\n':
      s &= state.consumeEscape()
    elif c in Ident:
      s &= c
    else:
      state.reconsume()
      break
  return s

proc consumeNumber(state: var CSSTokenizerState):
    tuple[isInt: bool; val: float32] =
  var isInt = true
  var repr = ""
  if state.has() and state.peek() in {'+', '-'}:
    repr &= state.consume()
  while state.has() and state.peek() in AsciiDigit:
    repr &= state.consume()
  if state.has(1) and state.peek() == '.' and state.peek(1) in AsciiDigit:
    repr &= state.consume()
    repr &= state.consume()
    isInt = false
    while state.has() and state.peek() in AsciiDigit:
      repr &= state.consume()
  if state.has(1) and state.peek() in {'E', 'e'} and
        state.peek(1) in AsciiDigit or
      state.has(2) and state.peek() in {'E', 'e'} and
        state.peek(1) in {'-', '+'} and state.peek(2) in AsciiDigit:
    repr &= state.consume()
    if state.peek() in {'-', '+'}:
      repr &= state.consume()
      repr &= state.consume()
    else:
      repr &= state.consume()
    isInt = false
    while state.has() and state.peek() in AsciiDigit:
      repr &= state.consume()
  let val = parseFloat32(repr)
  return (isInt, val)

proc consumeNumericToken(state: var CSSTokenizerState): CSSToken =
  let (isInt, val) = state.consumeNumber()
  if state.startsWithIdentSequence():
    let unit = state.consumeIdentSequence()
    if isInt:
      return CSSToken(t: cttIDimension, nvalue: val, unit: unit)
    return CSSToken(t: cttDimension, nvalue: val, unit: unit)
  if state.has() and state.peek() == '%':
    state.seek(1)
    return CSSToken(t: cttPercentage, nvalue: val)
  if isInt:
    return CSSToken(t: cttINumber, nvalue: val)
  return CSSToken(t: cttNumber, nvalue: val)

proc consumeBadURL(state: var CSSTokenizerState) =
  while state.has():
    let c = state.consume()
    if c == ')':
      break
    if c == '\\' and state.has() and state.peek() != '\n':
      discard state.consumeEscape()

const NonPrintable = {
  '\0'..char(0x08), '\v', char(0x0E)..char(0x1F), char(0x7F)
}

proc consumeURL(state: var CSSTokenizerState): CSSToken =
  let res = CSSToken(t: cttUrl)
  state.skipWhitespace()
  while state.has():
    let c = state.consume()
    case c
    of ')':
      return res
    of '"', '\'', '(', NonPrintable:
      state.consumeBadURL()
      return CSSToken(t: cttBadUrl)
    of AsciiWhitespace:
      state.skipWhitespace()
      if not state.has():
        return res
      if state.peek() == ')':
        state.seek(1)
        return res
      state.consumeBadURL()
      return CSSToken(t: cttBadUrl)
    of '\\':
      if state.has() and state.peek() != '\n':
        res.value &= state.consumeEscape()
      else:
        state.consumeBadURL()
        return CSSToken(t: cttBadUrl)
    else:
      res.value &= c
  return res

proc consumeIdentLikeToken(state: var CSSTokenizerState): CSSToken =
  let s = state.consumeIdentSequence()
  if s.equalsIgnoreCase("url") and state.has() and state.peek() == '(':
    state.seek(1)
    while state.has(1) and state.peek() in AsciiWhitespace and
        state.peek(1) in AsciiWhitespace:
      state.seek(1)
    if state.has() and state.peek() in {'"', '\''} or
        state.has(1) and state.peek() in {'"', '\''} + AsciiWhitespace and
        state.peek(1) in {'"', '\''}:
      return CSSToken(t: cttFunction, value: s)
    return state.consumeURL()
  if state.has() and state.peek() == '(':
    state.seek(1)
    return CSSToken(t: cttFunction, value: s)
  return CSSToken(t: cttIdent, value: s)

proc nextToken(state: var CSSTokenizerState): bool =
  while state.has(1) and state.peek() == '/' and state.peek(1) == '*':
    state.seek(2)
    while state.has() and not (state.has(1) and state.peek() == '*' and
        state.peek(1) == '/'):
      state.seek(1)
    if state.has(1):
      state.seek(1)
    if state.has():
      state.seek(1)
  return state.has()

proc consumeToken(state: var CSSTokenizerState): CSSToken =
  let c = state.consume()
  case c
  of AsciiWhitespace:
    state.skipWhitespace()
    return CSSToken(t: cttWhitespace)
  of '"', '\'':
    return consumeString(state, c)
  of '#':
    if state.has() and state.peek() in Ident or
        state.has(1) and state.peek() == '\\' and state.peek(1) != '\n':
      let flag = if state.startsWithIdentSequence():
        tflagaId
      else:
        tflagaUnrestricted
      return CSSToken(
        t: cttHash,
        value: state.consumeIdentSequence(),
        tflaga: flag
      )
    else:
      state.reconsume()
      return CSSToken(t: cttDelim, cvalue: state.consumeRChar())
  of '(': return CSSToken(t: cttLparen)
  of ')': return CSSToken(t: cttRparen)
  of '{': return CSSToken(t: cttLbrace)
  of '}': return CSSToken(t: cttRbrace)
  of '+':
    # starts with a number
    if state.has() and state.peek() in AsciiDigit or
        state.has(1) and state.peek() == '.' and state.peek(1) in AsciiDigit:
      state.reconsume()
      return state.consumeNumericToken()
    else:
      return CSSToken(t: cttDelim, cvalue: c)
  of ',': return CSSToken(t: cttComma)
  of '-':
    # starts with a number
    if state.has() and state.peek() in AsciiDigit or
        state.has(1) and state.peek() == '.' and state.peek(1) in AsciiDigit:
      state.reconsume()
      return state.consumeNumericToken()
    elif state.has(1) and state.peek() == '-' and state.peek(1) == '>':
      state.seek(2)
      return CSSToken(t: cttCdc)
    elif state.startsWithIdentSequenceDash():
      state.reconsume()
      return state.consumeIdentLikeToken()
    else:
      return CSSToken(t: cttDelim, cvalue: c)
  of '.':
    # starts with a number
    if state.has() and state.peek() in AsciiDigit:
      state.reconsume()
      return state.consumeNumericToken()
    else:
      return CSSToken(t: cttDelim, cvalue: c)
  of ':': return CSSToken(t: cttColon)
  of ';': return CSSToken(t: cttSemicolon)
  of '<':
    if state.has(2) and state.peek() == '!' and state.peek(1) == '-' and
        state.peek(2) == '-':
      state.seek(3)
      return CSSToken(t: cttCdo)
    else:
      return CSSToken(t: cttDelim, cvalue: c)
  of '@':
    if state.startsWithIdentSequence():
      let name = state.consumeIdentSequence()
      return CSSToken(t: cttAtKeyword, value: name)
    else:
      return CSSToken(t: cttDelim, cvalue: c)
  of '[': return CSSToken(t: cttLbracket)
  of '\\':
    if state.has() and state.peek() != '\n':
      state.reconsume()
      return state.consumeIdentLikeToken()
    else:
      return CSSToken(t: cttDelim, cvalue: c)
  of ']': return CSSToken(t: cttRbracket)
  of AsciiDigit:
    state.reconsume()
    return state.consumeNumericToken()
  of IdentStart:
    state.reconsume()
    return state.consumeIdentLikeToken()
  else:
    state.reconsume()
    return CSSToken(t: cttDelim, cvalue: state.consumeRChar())

proc tokenizeCSS(ibuf: string): seq[CSSComponentValue] =
  result = @[]
  var state = CSSTokenizerState(buf: ibuf)
  while state.nextToken():
    result.add(state.consumeToken())

proc consume(state: var CSSParseState): CSSComponentValue =
  result = state.tokens[state.at]
  inc state.at

proc reconsume(state: var CSSParseState) =
  dec state.at

func has(state: CSSParseState): bool =
  return state.at < state.tokens.len

func peek(state: CSSParseState): CSSComponentValue =
  return state.tokens[state.at]

proc skipWhitespace(state: var CSSParseState) =
  while state.has() and state.peek() == cttWhitespace:
    discard state.consume()

proc consumeComponentValue(state: var CSSParseState): CSSComponentValue

proc consumeSimpleBlock(state: var CSSParseState; tok: CSSToken):
    CSSSimpleBlock =
  var ending: CSSTokenType
  case tok.t
  of cttLbrace: ending = cttRbrace
  of cttLparen: ending = cttRparen
  of cttLbracket: ending = cttRbracket
  else: doAssert false
  result = CSSSimpleBlock(token: tok)
  while state.has():
    let tok = state.consume()
    if tok == ending:
      break
    elif tok == cttLbrace or tok == cttLbracket or tok == cttLparen:
      result.value.add(state.consumeSimpleBlock(CSSToken(tok)))
    else:
      state.reconsume()
      result.value.add(state.consumeComponentValue())

proc consumeFunction(state: var CSSParseState): CSSFunction =
  let t = CSSToken(state.consume())
  let name = parseEnumNoCase[CSSFunctionType](t.value).get(cftUnknown)
  let res = CSSFunction(name: name)
  while state.has():
    let t = state.consume()
    if t == cttRparen:
      break
    state.reconsume()
    res.value.add(state.consumeComponentValue())
  return res

proc consumeComponentValue(state: var CSSParseState): CSSComponentValue =
  let t = state.consume()
  if t == cttLbrace or t == cttLbracket or t == cttLparen:
    return state.consumeSimpleBlock(CSSToken(t))
  elif t == cttFunction:
    state.reconsume()
    return state.consumeFunction()
  return t

proc consumeQualifiedRule(state: var CSSParseState): Option[CSSQualifiedRule] =
  var r = CSSQualifiedRule()
  while state.has():
    let t = state.consume()
    if t of CSSSimpleBlock and CSSSimpleBlock(t).token == cttLbrace:
      r.oblock = CSSSimpleBlock(t)
      return some(r)
    elif t == cttLbrace:
      r.oblock = state.consumeSimpleBlock(CSSToken(t))
      return some(r)
    else:
      state.reconsume()
      r.prelude.add(state.consumeComponentValue())
  return none(CSSQualifiedRule)

proc consumeAtRule(state: var CSSParseState): CSSAtRule =
  let t = CSSToken(state.consume())
  result = CSSAtRule(name: t.value)
  while state.has():
    let t = state.consume()
    if t of CSSSimpleBlock:
      result.oblock = CSSSimpleBlock(t)
      break
    elif t == cttSemicolon:
      break
    elif t == cttLbrace:
      result.oblock = state.consumeSimpleBlock(CSSToken(t))
      break
    else:
      state.reconsume()
      result.prelude.add(state.consumeComponentValue())

proc consumeDeclaration(state: var CSSParseState): Option[CSSDeclaration] =
  let t = CSSToken(state.consume())
  var decl = CSSDeclaration(name: t.value)
  state.skipWhitespace()
  if not state.has() or state.peek() != cttColon:
    return none(CSSDeclaration)
  discard state.consume()
  state.skipWhitespace()
  while state.has():
    decl.value.add(state.consumeComponentValue())
  var i = decl.value.len - 1
  var j = 2
  var k = 0
  var l = 0
  while i >= 0 and j > 0:
    if decl.value[i] != cttWhitespace:
      dec j
      if decl.value[i] == cttIdent and k == 0:
        if CSSToken(decl.value[i]).value.equalsIgnoreCase("important"):
          inc k
          l = i
      elif k == 1 and decl.value[i] == cttDelim:
        if CSSToken(decl.value[i]).cvalue == '!':
          decl.important = true
          decl.value.delete(l)
          decl.value.delete(i)
          break
    dec i
  while decl.value.len > 0 and decl.value[^1] == cttWhitespace:
    decl.value.setLen(decl.value.len - 1)
  return some(decl)

# > Note: Despite the name, this actually parses a mixed list of
# > declarations and at-rules, as CSS 2.1 does for @page. Unexpected
# > at-rules (which could be all of them, in a given context) are
# > invalid and should be ignored by the consumer.
#
# Currently we never use nested at-rules, so the result of consumeAtRule
# is just discarded. This should be changed if we ever need nested at
# rules (e.g. add a flag to include at rules).
proc consumeDeclarations(state: var CSSParseState): seq[CSSDeclaration] =
  result = @[]
  while state.has():
    let t = state.consume()
    if t == cttWhitespace or t == cttSemicolon:
      continue
    elif t == cttAtKeyword:
      state.reconsume()
      discard state.consumeAtRule() # see above
    elif t == cttIdent:
      var tempList = @[t]
      while state.has() and state.peek() != cttSemicolon:
        tempList.add(state.consumeComponentValue())
      var tempState = CSSParseState(at: 0, tokens: tempList)
      let decl = tempState.consumeDeclaration()
      if decl.isSome:
        result.add(decl.get)
    else:
      state.reconsume()
      while state.has() and state.peek() != cttSemicolon:
        discard state.consumeComponentValue()

proc consumeListOfRules(state: var CSSParseState; topLevel = false):
    seq[CSSRule] =
  while state.has():
    let t = state.consume()
    if t == cttWhitespace:
      continue
    elif t == cttCdo or t == cttCdc:
      if topLevel:
        continue
      state.reconsume()
      let q = state.consumeQualifiedRule()
      if q.isSome:
        result.add(q.get)
    elif t == cttAtKeyword:
      state.reconsume()
      result.add(state.consumeAtRule())
    else:
      state.reconsume()
      let q = state.consumeQualifiedRule()
      if q.isSome:
        result.add(q.get)

proc parseStylesheet(state: var CSSParseState): CSSRawStylesheet =
  return CSSRawStylesheet(value: state.consumeListOfRules(true))

proc parseStylesheet*(ibuf: string): CSSRawStylesheet =
  var state = CSSParseState(tokens: tokenizeCSS(ibuf))
  return state.parseStylesheet()

proc parseListOfRules(state: var CSSParseState): seq[CSSRule] =
  return state.consumeListOfRules()

proc parseListOfRules*(cvals: seq[CSSComponentValue]): seq[CSSRule] =
  var state = CSSParseState(tokens: cvals)
  return state.parseListOfRules()

proc parseRule(state: var CSSParseState): DOMResult[CSSRule] =
  state.skipWhitespace()
  if not state.has():
    return errDOMException("Unexpected EOF", "SyntaxError")
  var res = if state.peek() == cttAtKeyword:
    state.consumeAtRule()
  else:
    let q = state.consumeQualifiedRule()
    if q.isNone:
      return errDOMException("No qualified rule found!", "SyntaxError")
    q.get
  state.skipWhitespace()
  if state.has():
    return errDOMException("EOF not reached", "SyntaxError")
  return ok(res)

proc parseRule*(ibuf: string): DOMResult[CSSRule] =
  var state = CSSParseState(tokens: tokenizeCSS(ibuf))
  return state.parseRule()

proc parseDeclarations*(cvals: seq[CSSComponentValue]): seq[CSSDeclaration] =
  var state = CSSParseState(tokens: cvals)
  return state.consumeDeclarations()

proc parseDeclarations*(ibuf: string): seq[CSSDeclaration] =
  return parseDeclarations(tokenizeCSS(ibuf))

proc parseComponentValue(state: var CSSParseState):
    DOMResult[CSSComponentValue] =
  state.skipWhitespace()
  if not state.has():
    return errDOMException("Unexpected EOF", "SyntaxError")
  let res = state.consumeComponentValue()
  state.skipWhitespace()
  if state.has():
    return errDOMException("EOF not reached", "SyntaxError")
  return ok(res)

proc parseComponentValue*(ibuf: string): DOMResult[CSSComponentValue] =
  var state = CSSParseState(tokens: tokenizeCSS(ibuf))
  return state.parseComponentValue()

proc parseComponentValues(state: var CSSParseState): seq[CSSComponentValue] =
  result = @[]
  while state.has():
    result.add(state.consumeComponentValue())

proc parseComponentValues*(ibuf: string): seq[CSSComponentValue] =
  var state = CSSParseState(tokens: tokenizeCSS(ibuf))
  return state.parseComponentValues()

proc nextCommaSepComponentValue(state: var CSSParseState;
    s: out seq[CSSComponentValue]): bool =
  s = @[]
  while state.has():
    let cvl = state.consumeComponentValue()
    if cvl == cttComma:
      break
    s.add(cvl)
  return s.len > 0

iterator parseCommaSepComponentValues*(cvals: seq[CSSComponentValue]):
    seq[CSSComponentValue] =
  var state = CSSParseState(tokens: cvals)
  var s: seq[CSSComponentValue]
  while state.nextCommaSepComponentValue(s):
    yield move(s)

proc parseAnB*(state: var CSSParseState): Option[CSSAnB] =
  template is_eof: bool =
    not state.has() or not (state.peek() of CSSToken)
  template fail_eof =
    if is_eof:
      return none(CSSAnB)
  template get_plus: bool =
    let tok = state.peek()
    if tok == cttDelim and CSSToken(tok).cvalue == '+':
      discard state.consume()
      true
    else:
      false
  template get_tok: CSSToken =
    state.skipWhitespace()
    fail_eof
    CSSToken(state.consume())
  template get_tok_nows: CSSToken =
    fail_eof
    CSSToken(state.consume())
  template fail_plus =
    if is_plus:
      return none(CSSAnB)
  template parse_sub_int(sub: string; skip: int): int32 =
    let s = sub.substr(skip)
    let x = parseInt32(s)
    if x.isNone:
      return none(CSSAnB)
    x.get
  template fail_non_integer(tok: CSSToken; res: Option[CSSAnB]) =
    if tok.t != cttINumber:
      state.reconsume()
      return res
    if int64(tok.nvalue) > high(int):
      state.reconsume()
      return res
  template fail_non_signless_integer(tok: CSSToken; res: Option[CSSAnB]) =
    fail_non_integer tok, res #TODO check if signless?

  fail_eof
  state.skipWhitespace()
  fail_eof
  let is_plus = get_plus
  let tok = get_tok_nows
  case tok.t
  of cttIdent:
    case tok.value
    of "odd":
      fail_plus
      return some((2i32, 1i32))
    of "even":
      fail_plus
      return some((2i32, 0i32))
    of "n", "N":
      state.skipWhitespace()
      if is_eof:
        return some((1i32, 0i32))
      let tok2 = get_tok_nows
      if tok2.t == cttDelim:
        let sign = case tok2.cvalue
        of '+': 1i32
        of '-': -1i32
        else: return none(CSSAnB)
        let tok3 = get_tok
        fail_non_signless_integer tok3, some((1i32, 0i32))
        return some((1i32, sign * int32(tok3.nvalue)))
      else:
        fail_non_integer tok2, some((1i32, 0i32))
        return some((1i32, int32(tok2.nvalue)))
    of "-n", "-N":
      fail_plus
      state.skipWhitespace()
      if is_eof:
        return some((-1i32, 0i32))
      let tok2 = get_tok_nows
      if tok2.t == cttDelim:
        let sign = case tok2.cvalue
        of '+': 1i32
        of '-': -1i32
        else: return none(CSSAnB)
        let tok3 = get_tok
        fail_non_signless_integer tok3, some((-1i32, 0i32))
        return some((-1i32, sign * int32(tok3.nvalue)))
      else:
        fail_non_integer tok2, some((-1i32, 0i32))
        return some((-1i32, int32(tok2.nvalue)))
    of "n-", "N-":
      let tok2 = get_tok
      fail_non_signless_integer tok2, none(CSSAnB)
      return some((1i32, -int32(tok2.nvalue)))
    of "-n-", "-N-":
      fail_plus
      let tok2 = get_tok
      fail_non_signless_integer tok2, none(CSSAnB)
      return some((-1i32, -int32(tok2.nvalue)))
    elif tok.value.startsWithIgnoreCase("n-"):
      return some((1i32, -parse_sub_int(tok.value, "n-".len)))
    elif tok.value.startsWithIgnoreCase("-n-"):
      fail_plus
      return some((-1i32, -parse_sub_int(tok.value, "n-".len)))
    else:
      return none(CSSAnB)
  of cttINumber:
    fail_plus
    # <integer>
    return some((0i32, int32(tok.nvalue)))
  of cttIDimension:
    fail_plus
    case tok.unit
    of "n", "N":
      # <n-dimension>
      state.skipWhitespace()
      if is_eof:
        return some((int32(tok.nvalue), 0i32))
      let tok2 = get_tok_nows
      if tok2.t == cttDelim:
        let sign = case tok2.cvalue
        of '+': 1i32
        of '-': -1i32
        else: return none(CSSAnB)
        let tok3 = get_tok
        fail_non_signless_integer tok3, some((int32(tok.nvalue), 0i32))
        return some((int32(tok.nvalue), sign * int32(tok3.nvalue)))
      else:
        fail_non_integer tok2, some((int32(tok.nvalue), 0i32))
        return some((int32(tok.nvalue), int32(tok2.nvalue)))
    of "n-", "N-":
      # <ndash-dimension>
      let tok2 = get_tok
      fail_non_signless_integer tok2, none(CSSAnB)
      return some((int32(tok.nvalue), -int32(tok2.nvalue)))
    elif tok.unit.startsWithIgnoreCase("n-"):
      # <ndashdigit-dimension>
      return some((int32(tok.nvalue), -parse_sub_int(tok.unit, "n-".len)))
    else:
      return none(CSSAnB)
  else:
    return none(CSSAnB)

proc parseAnB*(cvals: seq[CSSComponentValue]): (Option[CSSAnB], int) =
  var state = CSSParseState(tokens: cvals)
  let anb = state.parseAnB()
  return (anb, state.at)