parse-css.js

"use strict";
(function (global, factory) {
  if (typeof exports === 'object' && typeof module === 'object') {
    // CommonJS/Node.js
    Object.assign(exports, factory());
  } else if (typeof define === 'function' && define.amd) {
    // AMD
    define(factory);
  } else {
    // browser global
    global = typeof globalThis !== 'undefined' ? globalThis : global || self;
    global.parseCss = factory();
  }
}(this, function (exports) {

const config = {
  tokenizeErrorHandler: null,
  parseErrorHandler: null,
};

function between(num, first, last) { return num >= first && num <= last; }
function digit(code) { return between(code, 0x30,0x39); }
function hexdigit(code) { return digit(code) || between(code, 0x41,0x46) || between(code, 0x61,0x66); }
function uppercaseletter(code) { return between(code, 0x41,0x5a); }
function lowercaseletter(code) { return between(code, 0x61,0x7a); }
function letter(code) { return uppercaseletter(code) || lowercaseletter(code); }
function nonascii(code) {
  return (
    code == 0xb7 ||
    between(code, 0xc0, 0xd6) ||
    between(code, 0xd8, 0xf6) ||
    between(code, 0xf8, 0x37d) ||
    between(code, 0x37f, 0x1fff) ||
    code == 0x200c ||
    code == 0x200d ||
    code == 0x203f ||
    code == 0x2040 ||
    between(code, 0x2070, 0x218f) ||
    between(code, 0x2c00, 0x2fef) ||
    between(code, 0x3001, 0xd7ff) ||
    between(code, 0xf900, 0xfdcf) ||
    between(code, 0xfdf0, 0xfffd) ||
    code >= 0x10000
  );
}
function namestartchar(code) { return letter(code) || nonascii(code) || code == 0x5f; }
function namechar(code) { return namestartchar(code) || digit(code) || code == 0x2d; }
function nonprintable(code) { return between(code, 0,8) || code == 0xb || between(code, 0xe,0x1f) || code == 0x7f; }
function newline(code) { return code == 0xa; }
function whitespace(code) { return newline(code) || code == 9 || code == 0x20; }
function badescape(code) { return newline(code) || isNaN(code); }
function surrogate(code) { return between(code, 0xd800, 0xdfff); }

var maximumallowedcodepoint = 0x10ffff;

class InvalidCharacterError extends Error {
  constructor(message) {
    super();
    this.name = "InvalidCharacterError";
    this.message = message;
  }
}

class SpecError extends Error {
  constructor(...args) {
    super(...args);
    this.name = "SpecError";
  }
}

function preprocess(str) {
  // Turn a string into an array of code points,
  // following the preprocessing cleanup rules.
  var codepoints = [];
  for(var i = 0; i < str.length; i++) {
    var code = str.codePointAt(i);
    if (code == 0xd && str.charCodeAt(i+1) == 0xa) {
      code = 0xa; i++;
    } else if (code == 0xd || code == 0xc) {
      code = 0xa;
    } else if (code == 0x0 || between(code, 0xd800, 0xdfff)) {
      code = 0xfffd;
    } else if (code > 0xffff) {
      i++;
    }
    codepoints.push(code);
  }
  return codepoints;
}

function asciiCaselessMatch(s1, s2) {
  return s1.toLowerCase() == s2.toLowerCase();
}

function tokenize(str) {
  str = preprocess(str);
  var i = -1;
  var tokens = [];
  var code;

  // Line number information.
  var line = 0;
  var column = 0;
  // The only use of lastLineLength is in reconsume().
  var lastLineLength = 0;
  var incrLineno = function() {
    line += 1;
    lastLineLength = column;
    column = 0;
  };
  var locStart = {line:line, column:column};

  var codepoint = function(i) {
    if(i >= str.length) {
      return -1;
    }
    return str[i];
  }
  var next = function(num) {
    if(num === undefined)
      num = 1;
    if(num > 3)
      throw new SpecError("no more than three codepoints of lookahead.");
    return codepoint(i+num);
  };
  var consume = function(num) {
    if(num === undefined)
      num = 1;
    i += num;
    code = codepoint(i);
    if(newline(code)) incrLineno();
    else column += num;
    //console.log('Consume '+i+' '+String.fromCharCode(code) + ' 0x' + code.toString(16));
    return true;
  };
  var reconsume = function() {
    i -= 1;
    if (newline(code)) {
      line -= 1;
      column = lastLineLength;
    } else {
      column -= 1;
    }
    locStart.line = line;
    locStart.column = column;
    return true;
  };
  var eof = function(codepoint) {
    if(codepoint === undefined) codepoint = code;
    return codepoint == -1;
  };
  var donothing = function() {};
  var parseerror = function() {
    if (typeof config.tokenizeErrorHandler === 'function') {
      return config.tokenizeErrorHandler(i, code);
    }
    console.log("Parse error at index " + i + ", processing codepoint 0x" + code.toString(16) + ".");
    return true;
  };

  var consumeAToken = function() {
    consumeComments();
    consume();
    if(whitespace(code)) {
      while(whitespace(next())) consume();
      return new WhitespaceToken;
    }
    else if(code == 0x22) return consumeAStringToken();
    else if(code == 0x23) {
      if(namechar(next()) || areAValidEscape(next(1), next(2))) {
        const isIdent = wouldStartAnIdentifier(next(1), next(2), next(3));
        return new HashToken(consumeAName(), isIdent);
      } else {
        return new DelimToken(code);
      }
    }
    else if(code == 0x27) return consumeAStringToken();
    else if(code == 0x28) return new OpenParenToken();
    else if(code == 0x29) return new CloseParenToken();
    else if(code == 0x2b) {
      if(startsWithANumber()) {
        reconsume();
        return consumeANumericToken();
      } else {
        return new DelimToken(code);
      }
    }
    else if(code == 0x2c) return new CommaToken();
    else if(code == 0x2d) {
      if(startsWithANumber()) {
        reconsume();
        return consumeANumericToken();
      } else if(next(1) == 0x2d && next(2) == 0x3e) {
        consume(2);
        return new CDCToken();
      } else if(startsWithAnIdentifier()) {
        reconsume();
        return consumeAnIdentlikeToken();
      } else {
        return new DelimToken(code);
      }
    }
    else if(code == 0x2e) {
      if(startsWithANumber()) {
        reconsume();
        return consumeANumericToken();
      } else {
        return new DelimToken(code);
      }
    }
    else if(code == 0x3a) return new ColonToken;
    else if(code == 0x3b) return new SemicolonToken;
    else if(code == 0x3c) {
      if(next(1) == 0x21 && next(2) == 0x2d && next(3) == 0x2d) {
        consume(3);
        return new CDOToken();
      } else {
        return new DelimToken(code);
      }
    }
    else if(code == 0x40) {
      if(wouldStartAnIdentifier(next(1), next(2), next(3))) {
        return new AtKeywordToken(consumeAName());
      } else {
        return new DelimToken(code);
      }
    }
    else if(code == 0x5b) return new OpenSquareToken();
    else if(code == 0x5c) {
      if(startsWithAValidEscape()) {
        reconsume();
        return consumeAnIdentlikeToken();
      } else {
        parseerror();
        return new DelimToken(code);
      }
    }
    else if(code == 0x5d) return new CloseSquareToken();
    else if(code == 0x7b) return new OpenCurlyToken();
    else if(code == 0x7d) return new CloseCurlyToken();
    else if(digit(code)) {
      reconsume();
      return consumeANumericToken();
    }
    else if(namestartchar(code)) {
      reconsume();
      return consumeAnIdentlikeToken();
    }
    else if(eof()) return new EOFToken();
    else return new DelimToken(code);
  };

  var consumeComments = function() {
    while(next(1) == 0x2f && next(2) == 0x2a) {
      consume(2);
      while(true) {
        consume();
        if(code == 0x2a && next() == 0x2f) {
          consume();
          break;
        } else if(eof()) {
          parseerror();
          return;
        }
      }
    }
  };

  var consumeANumericToken = function() {
    var {value, isInteger, sign} = consumeANumber();
    if(wouldStartAnIdentifier(next(1), next(2), next(3))) {
      const unit = consumeAName();
      return new DimensionToken(value, isInteger, unit, sign);
    } else if(next() == 0x25) {
      consume();
      return new PercentageToken(value, sign);
    } else {
      return new NumberToken(value, isInteger, sign);
    }
  };

  var consumeAnIdentlikeToken = function() {
    var str = consumeAName();
    if(str.toLowerCase() == "url" && next() == 0x28) {
      consume();
      while(whitespace(next(1)) && whitespace(next(2))) consume();
      if(next() == 0x22 || next() == 0x27) {
        return new FunctionToken(str);
      } else if(whitespace(next()) && (next(2) == 0x22 || next(2) == 0x27)) {
        return new FunctionToken(str);
      } else {
        return consumeAURLToken();
      }
    } else if(next() == 0x28) {
      consume();
      return new FunctionToken(str);
    } else {
      return new IdentToken(str);
    }
  };

  var consumeAStringToken = function(endingCodePoint) {
    if(endingCodePoint === undefined) endingCodePoint = code;
    var string = "";
    while(consume()) {
      if(code == endingCodePoint || eof()) {
        return new StringToken(string);
      } else if(newline(code)) {
        parseerror();
        reconsume();
        return new BadStringToken();
      } else if(code == 0x5c) {
        if(eof(next())) {
          donothing();
        } else if(newline(next())) {
          consume();
        } else {
          string += String.fromCodePoint(consumeEscape())
        }
      } else {
        string += String.fromCodePoint(code);
      }
    }
  };

  var consumeAURLToken = function() {
    var token = new URLToken("");
    while(whitespace(next())) consume();
    if(eof(next())) return token;
    while(consume()) {
      if(code == 0x29 || eof()) {
        return token;
      } else if(whitespace(code)) {
        while(whitespace(next())) consume();
        if(next() == 0x29 || eof(next())) {
          consume();
          return token;
        } else {
          consumeTheRemnantsOfABadURL();
          return new BadURLToken();
        }
      } else if(code == 0x22 || code == 0x27 || code == 0x28 || nonprintable(code)) {
        parseerror();
        consumeTheRemnantsOfABadURL();
        return new BadURLToken();
      } else if(code == 0x5c) {
        if(startsWithAValidEscape()) {
          token.value += String.fromCodePoint(consumeEscape());
        } else {
          parseerror();
          consumeTheRemnantsOfABadURL();
          return new BadURLToken();
        }
      } else {
        token.value += String.fromCodePoint(code);
      }
    }
  };

  var consumeEscape = function() {
    // Assume the the current character is the \
    // and the next code point is not a newline.
    consume();
    if(hexdigit(code)) {
      // Consume 1-6 hex digits
      var digits = [code];
      for(var total = 0; total < 5; total++) {
        if(hexdigit(next())) {
          consume();
          digits.push(code);
        } else {
          break;
        }
      }
      if(whitespace(next())) consume();
      var value = parseInt(digits.map(function(x){return String.fromCharCode(x);}).join(''), 16);
      if (value === 0x0 || between(value, 0xd800, 0xdfff) || value > maximumallowedcodepoint ) value = 0xfffd;
      return value;
    } else if(eof()) {
      return 0xfffd;
    } else {
      return code;
    }
  };

  var areAValidEscape = function(c1, c2) {
    if(c1 != 0x5c) return false;
    if(newline(c2)) return false;
    return true;
  };
  var startsWithAValidEscape = function() {
    return areAValidEscape(code, next());
  };

  var wouldStartAnIdentifier = function(c1, c2, c3) {
    if(c1 == 0x2d) {
      return namestartchar(c2) || c2 == 0x2d || areAValidEscape(c2, c3);
    } else if(namestartchar(c1)) {
      return true;
    } else if(c1 == 0x5c) {
      return areAValidEscape(c1, c2);
    } else {
      return false;
    }
  };
  var startsWithAnIdentifier = function() {
    return wouldStartAnIdentifier(code, next(1), next(2));
  };

  var wouldStartANumber = function(c1, c2, c3) {
    if(c1 == 0x2b || c1 == 0x2d) {
      if(digit(c2)) return true;
      if(c2 == 0x2e && digit(c3)) return true;
      return false;
    } else if(c1 == 0x2e) {
      if(digit(c2)) return true;
      return false;
    } else if(digit(c1)) {
      return true;
    } else {
      return false;
    }
  };
  var startsWithANumber = function() {
    return wouldStartANumber(code, next(1), next(2));
  };

  var consumeAName = function() {
    var result = "";
    while(consume()) {
      if(namechar(code)) {
        result += String.fromCodePoint(code);
      } else if(startsWithAValidEscape()) {
        result += String.fromCodePoint(consumeEscape());
      } else {
        reconsume();
        return result;
      }
    }
  };

  var consumeANumber = function() {
    let isInteger = true;
    let sign;
    let numberPart = "";
    let exponentPart = "";
    if(next() == 0x2b || next() == 0x2d) {
      consume();
      sign = String.fromCodePoint(code);
      numberPart += sign;
    }
    while(digit(next())) {
      consume();
      numberPart += String.fromCodePoint(code);
    }
    if(next(1) == 0x2e && digit(next(2))) {
      consume();
      numberPart += ".";
      while(digit(next())) {
        consume();
        numberPart += String.fromCodePoint(code);
      }
      isInteger = false;
    }
    var c1 = next(1), c2 = next(2), c3 = next(3);
    const eDigit = (c1 == 0x45 || c1 == 0x65) && digit(c2);
    const eSignDigit = (c1 == 0x45 || c1 == 0x65) && (c2 == 0x2b || c2 == 0x2d) && digit(c3);
    if(eDigit || eSignDigit) {
      consume();
      if(eSignDigit) {
        consume();
        exponentPart += String.fromCodePoint(code);
      }
      while(digit(next())) {
        consume();
        exponentPart += String.fromCodePoint(code);
      }
      isInteger = false;
    }

    // parse with native engine to prevent a precision issue
    // (e.g. 12E-1 becomes 1.2000000000000002)
    let value = Number(numberPart + (exponentPart ? 'e' + exponentPart : ''));
    // let value = +numberPart;
    // if(exponentPart) value = value * Math.pow(10, +exponentPart);

    return {value, isInteger, sign};
  };

  var consumeTheRemnantsOfABadURL = function() {
    while(consume()) {
      if(code == 0x29 || eof()) {
        return;
      } else if(startsWithAValidEscape()) {
        consumeEscape();
        donothing();
      } else {
        donothing();
      }
    }
  };



  var iterationCount = 0;
  while (true) {
    var token = consumeAToken();
    tokens.push(token);
    if (token instanceof EOFToken) {
      break;
    }
    iterationCount++;
    if(iterationCount > str.length*2) throw new Error("I'm infinite-looping!");
  }
  return tokens;
}

class CSSParserToken {
  constructor(type) {
    this.type = type;
  }

  toJSON() { return {type:this.type}; }
  toString() { return this.type; }
  toSource() { throw new Error("Not implemented."); }
}
//toJSON()
//toString()
//toSource()

class BadStringToken extends CSSParserToken {
  constructor() {
    super("BADSTRING");
  }
  toSource() { return '"\n'; }
}

class BadURLToken extends CSSParserToken {
  constructor() {
    super("BADURL");
  }
  toSource() { return "url(BAD URL)"}
}
BadURLToken.prototype.tokenType = "BADURL";

class WhitespaceToken extends CSSParserToken {
  constructor() {
    super("WHITESPACE");
  }
  toString() { return "WS"; }
  toSource() { return " "; }
}

class CDOToken extends CSSParserToken {
  constructor() {
    super("CDO");
  }
  toSource() { return "<!--"; }
}

class CDCToken extends CSSParserToken {
  constructor() {
    super("CDC");
  }
  toSource() { return "-->"; }
}

class ColonToken extends CSSParserToken {
  constructor() {
    super("COLON");
  }
  toSource() { return ":"; }
}

class SemicolonToken extends CSSParserToken {
  constructor() {
    super("SEMICOLON");
  }
  toSource() { return ";" };
}

class CommaToken extends CSSParserToken {
  constructor() {
    super("COMMA");
  }
  toSource() { return "," }
}

class OpenCurlyToken extends CSSParserToken {
  constructor() {
    super("OPEN-CURLY");
    this.grouping = true;
    this.mirror = CloseCurlyToken;
  }
  toSource() { return "{"; }
}

class CloseCurlyToken extends CSSParserToken {
  constructor() {
    super("CLOSE-CURLY");
  }
  toSource() { return "}"; }
}

class OpenSquareToken extends CSSParserToken {
  constructor() {
    super("OPEN-SQUARE");
    this.grouping = true;
    this.mirror = CloseSquareToken;
  }
  toSource() { return "["; }
}

class CloseSquareToken extends CSSParserToken {
  constructor() {
    super("CLOSE-SQUARE");
  }
  toSource() { return "]"; }
}

class OpenParenToken extends CSSParserToken {
  constructor() {
    super("OPEN-PAREN");
    this.grouping = true;
    this.mirror = CloseParenToken;
  }
  toSource() { return "("; }
}

class CloseParenToken extends CSSParserToken {
  constructor() {
    super("CLOSE-PAREN");
  }
  toSource() { return ")"; }
}

class EOFToken extends CSSParserToken {
  constructor() {
    super("EOF");
  }
  toSource() { return ""; }
}

class DelimToken extends CSSParserToken {
  constructor(val) {
    super("DELIM");
    if(typeof val == "number") {
      val = String.fromCodePoint(val);
    } else {
      val = String(val);
    }
    this.value = val;
  }
  toString() { return `DELIM(${this.value})`; }
  toJSON() { return {type:this.type, value:this.value}; }
  toSource() {
    if(this.value == "\\") return "\\\n";
    return this.value;
  }
}

class IdentToken extends CSSParserToken {
  constructor(val) {
    super("IDENT");
    this.value = val;
  }
  toString() { return `IDENT(${this.value})`; }
  toJSON() { return {type:this.type, value:this.value}; }
  toSource() { return escapeIdent(this.value); }
}

class FunctionToken extends CSSParserToken {
  constructor(val) {
    super("FUNCTION");
    this.value = val;
    this.mirror = CloseParenToken;
  }
  toString() { return `FUNCTION(${this.value})`; }
  toJSON() { return {type:this.type, value:this.value}; }
  toSource() { return escapeIdent(this.value) + "("; }
}

class AtKeywordToken extends CSSParserToken {
  constructor(val) {
    super("AT-KEYWORD");
    this.value = val;
  }
  toString() { return `AT(${this.value})`; }
  toJSON() { return {type:this.type, value:this.value }; }
  toSource() { return "@" + escapeIdent(this.value); }
}

class HashToken extends CSSParserToken {
  constructor(val, isIdent) {
    super("HASH");
    this.value = val;
    this.isIdent = isIdent;
  }
  toString() { return `HASH(${this.value})`; }
  toJSON() { return {type:this.type, value:this.value, isIdent:this.isIdent}; }
  toSource() {
    if(this.isIdent) {
      return "#" + escapeIdent(this.value);
    }
    return "#" + escapeHash(this.value);
  }
}

class StringToken extends CSSParserToken {
  constructor(val) {
    super("STRING");
    this.value = val;
  }
  toString() { return `STRING(${this.value})`; }
  toJSON() { return {type:this.type, value:this.value}; }
  toSource() { return `"${escapeString(this.value)}"`; }
}

class URLToken extends CSSParserToken {
  constructor(val) {
    super("URL");
    this.value = val;
  }
  toString() { return `URL(${this.value})`; }
  toJSON() { return {type:this.type, value:this.value}; }
  toSource() { return `url("${escapeString(this.value)}")`; }
}

class NumberToken extends CSSParserToken {
  constructor(val, isInteger, sign=undefined) {
    super("NUMBER");
    this.value = val;
    this.isInteger = isInteger;
    this.sign = sign;
  }
  toString() {
    const name = this.isInteger ? "INT" : "NUMBER";
    const sign = this.sign == "+" ? "+" : "";
    return `${name}(${sign}${this.value})`;
  }
  toJSON() { return {type:this.type, value:this.value, isInteger:this.isInteger, sign:this.sign}; }
  toSource() { return formatNumber(this.value, this.sign); }
}

class PercentageToken extends CSSParserToken {
  constructor(val, sign=undefined) {
    super("PERCENTAGE");
    this.value = val;
    this.sign = sign;
  }
  toString() {
    const sign = this.sign == "+" ? "+" : "";
    return `PERCENTAGE(${sign}${this.value})`;
  }
  toJSON() { return {type:this.type, value:this.value, sign:this.sign}; }
  toSource() { return `${formatNumber(this.value, this.sign)}%`; }
}

class DimensionToken extends CSSParserToken {
  constructor(val, isInteger, unit, sign=undefined) {
    super("DIMENSION");
    this.value = val;
    this.isInteger = isInteger;
    this.unit = unit;
    this.sign = sign;
  }
  toString() {
    const sign = this.sign == "+" ? "+" : "";
    return `DIM(${sign}${this.value}, ${this.unit})`;
  }
  toJSON() { return {type:this.type, value:this.value, isInteger:this.isInteger, unit:this.unit, sign:this.sign}; }
  toSource() {
    let unit = escapeIdent(this.unit);
    if(unit[0].toLowerCase() == "e" && (unit[1] == "-" || digit(unit[1].charCodeAt(0)))) {
      // Unit is ambiguous with scinot
      // Remove the leading "e", replace with escape.
      unit = "\\65 " + unit.slice(1, unit.length);
    }
    return `${formatNumber(this.value, this.sign)}${unit}`;
  }
}

function escapeIdent(string) {
  return Array.from(String(string), (e,i)=>{
    const code = e.codePointAt(0);
    if(i == 0) {
      if(namestartchar(code)) return e;
      return escapeIdentCode(code);
    }
    if(namechar(code)) return e;
    return escapeIdentCode(code);
  }).join("");
}

function escapeIdentCode(code) {
  if(digit(code) || letter(code)) {
    return `\\${code.toString(16)} `;
  }
  return "\\"+String.fromCodePoint(code);
}

function escapeHash(string) {
  // Escapes the value (after the #) of a hash.
  return Array.from(String(string), e=>{
    const code = e.codePointAt(0);
    if(namechar(code)) return e;
    return escapeIdentCode(code);
  }).join("");
}

function escapeString(string) {
  // Escapes the contents (between the quotes) of a string
  return Array.from(String(string), e=>{
    const code = e.codePointAt(0);
    if(between(code, 0x0, 0x1f)
      || code == 0x7f
      || code == 0x22
      || code == 0x5c
    ) {
      return "\\" + code.toString(16) + " ";
    }
    return e;
  }).join("");
}

function formatNumber(num, sign=undefined) {
  // TODO: Fix this to match CSS stringification behavior.
  return (sign == "+" ? "+" : "") + String(num);
}

class TokenStream {
  constructor(tokens) {
    // Assume that tokens is an array.
    this.tokens = tokens;
    this.i = 0;
    this.marks = [];
  }
  nextToken() {
    if(this.i < this.tokens.length) return this.tokens[this.i];
    return new EOFToken();
  }
  empty() {
    return this.i >= this.tokens.length;
  }
  consumeToken() {
    const tok = this.nextToken();
    this.i++;
    return tok;
  }
  discardToken() {
    this.i++;
  }
  mark() {
    this.marks.push(this.i);
    return this;
  }
  restoreMark() {
    if(this.marks.length) {
      this.i = this.marks.pop();
      return this;
    }
    throw new Error("No marks to restore.");
  }
  discardMark() {
    if(this.marks.length) {
      this.marks.pop();
      return this;
    }
    throw new Error("No marks to restore.");
  }
  discardWhitespace() {
    while(this.nextToken() instanceof WhitespaceToken) {
      this.discardToken();
    }
    return this;
  }
}

function parseerror(stream, msg) {
  const index = stream.i;
  const token = stream.tokens[index];
  if (typeof config.parseErrorHandler === 'function') {
    return config.parseErrorHandler(index, token, msg);
  }
  console.log("Parse error at token " + index + ": " + token + ".\n" + msg);
  return true;
}

function consumeAStylesheetsContents(s) {
  const rules = [];
  while(1) {
    const token = s.nextToken();
    if(token instanceof WhitespaceToken) {
      s.discardToken();
    } else if(token instanceof EOFToken) {
      return rules;
    } else if(token instanceof CDOToken || token instanceof CDCToken) {
      s.discardToken();
    } else if(token instanceof AtKeywordToken) {
      const rule = consumeAnAtRule(s)
      if(rule) rules.push(rule);
    } else {
      const rule = consumeAQualifiedRule(s);
      if(rule) rules.push(rule);
    }
  }
}

function consumeAnAtRule(s, nested=false) {
  const token = s.consumeToken();
  if(!(token instanceof AtKeywordToken))
    throw new Error("consumeAnAtRule() called with an invalid token stream state.");
  const rule = new AtRule(token.value);
  while(1) {
    const token = s.nextToken();
    if(token instanceof SemicolonToken || token instanceof EOFToken) {
      s.discardToken();
      return filterValid(rule);
    } else if(token instanceof CloseCurlyToken) {
      if(nested) return filterValid(rule);
      else {
        parseerror(s, "Hit an unmatched } in the prelude of an at-rule.");
        rule.prelude.push(s.consumeToken());
      }
    } else if(token instanceof OpenCurlyToken) {
      [rule.declarations, rule.rules] = consumeABlock(s);
      return filterValid(rule);
    } else {
      rule.prelude.push(consumeAComponentValue(s));
    }
  }
}

function consumeAQualifiedRule(s, nested=false, stopToken=EOFToken) {
  var rule = new QualifiedRule();
  while(1) {
    const token = s.nextToken();
    if(token instanceof EOFToken || token instanceof stopToken) {
      parseerror(s, "Hit EOF or semicolon when trying to parse the prelude of a qualified rule.");
      return;
    } else if(token instanceof CloseCurlyToken) {
      parseerror(s, "Hit an unmatched } in the prelude of a qualified rule.");
      if(nested) return;
      else {
        rule.prelude.push(s.consumeToken());
      }
    } else if(token instanceof OpenCurlyToken) {
      if(looksLikeACustomProperty(rule.prelude)) {
        consumeTheRemnantsOfABadDeclaration(s, nested);
        return;
      }
      [rule.declarations, rule.rules] = consumeABlock(s);
      return filterValid(rule);
    } else {
      rule.prelude.push(consumeAComponentValue(s));
    }
  }
}

function looksLikeACustomProperty(tokens) {
  let foundDashedIdent = false;
  for(const token of tokens) {
    if(token instanceof WhitespaceToken) continue;
    if(!foundDashedIdent && token instanceof IdentToken && token.value.slice(0, 2) == "--") {
      foundDashedIdent = true;
      continue;
    }
    if(foundDashedIdent && token instanceof ColonToken) {
      return true;
    }
    return false;
  }
  return false;
}

function consumeABlock(s) {
  if(!(s.nextToken() instanceof OpenCurlyToken)) {
    throw new Error("consumeABlock() called with an invalid token stream state.");
  }
  s.discardToken();
  const [decls, rules] = consumeABlocksContents(s);
  s.discardToken();
  return [decls, rules];
}

function consumeABlocksContents(s) {
  const decls = [];
  const rules = [];
  while(1) {
    const token = s.nextToken();
    if(token instanceof WhitespaceToken || token instanceof SemicolonToken) {
      s.discardToken();
    } else if(token instanceof EOFToken || token instanceof CloseCurlyToken) {
      return [decls, rules];
    } else if(token instanceof AtKeywordToken) {
      const rule = consumeAnAtRule(s, true);
      if(rule) rules.push(rule);
    } else {
      s.mark();
      const decl = consumeADeclaration(s, true);
      if(decl) {
        decls.push(decl);
        s.discardMark();
        continue;
      }
      s.restoreMark();
      const rule = consumeAQualifiedRule(s, true, SemicolonToken);
      if(rule) rules.push(rule);
    }
  }
}

function consumeADeclaration(s, nested=false) {
  let decl;
  if(s.nextToken() instanceof IdentToken) {
    decl = new Declaration(s.consumeToken().value);
  } else {
    consumeTheRemnantsOfABadDeclaration(s, nested);
    return;
  }
  s.discardWhitespace();
  if(s.nextToken() instanceof ColonToken) {
    s.discardToken();
  } else {
    consumeTheRemnantsOfABadDeclaration(s, nested);
    return;
  }
  s.discardWhitespace();
  decl.value = consumeAListOfComponentValues(s, nested, SemicolonToken);

  var foundImportant = false;
  for(var i = decl.value.length - 1; i >= 0; i--) {
    if(decl.value[i] instanceof WhitespaceToken) {
      continue;
    } else if(!foundImportant && decl.value[i] instanceof IdentToken && asciiCaselessMatch(decl.value[i].value, "important")) {
      foundImportant = true;
    } else if(foundImportant && decl.value[i] instanceof DelimToken && decl.value[i].value == "!") {
      decl.value.length = i;
      decl.important = true;
      break;
    } else {
      break;
    }
  }

  var i = decl.value.length - 1;
  while(decl.value[i] instanceof WhitespaceToken) {
    decl.value.length = i;
    i--;
  }
  return filterValid(decl);
}

function consumeTheRemnantsOfABadDeclaration(s, nested) {
  while(1) {
    const token = s.nextToken();
    if(token instanceof EOFToken || token instanceof SemicolonToken) {
      s.discardToken();
      return;
    } else if(token instanceof CloseCurlyToken) {
      if(nested) return;
      else s.discardToken();
    } else {
      consumeAComponentValue(s);
    }
  }
}

function consumeAListOfComponentValues(s, nested=false, stopToken=EOFToken) {
  const values = [];
  while(1) {
    const token = s.nextToken();
    if(token instanceof EOFToken || token instanceof stopToken) {
      return values;
    } else if(token instanceof CloseCurlyToken) {
      if(nested) return values;
      else {
        parseerror(s, "Hit an unmatched } in a declaration value.");
        values.push(s.consumeToken());
      }
    } else {
      values.push(consumeAComponentValue(s));
    }
  }
}

function consumeAComponentValue(s) {
  const token = s.nextToken();
  if(token instanceof OpenCurlyToken || token instanceof OpenSquareToken || token instanceof OpenParenToken)
    return consumeASimpleBlock(s);
  if(token instanceof FunctionToken)
    return consumeAFunction(s);
  return s.consumeToken();
}

function consumeASimpleBlock(s) {
  if(!s.nextToken().mirror) {
    throw new Error("consumeASimpleBlock() called with an invalid token stream state.");
  }
  const start = s.nextToken();
  const block = new SimpleBlock(start.toSource());
  s.discardToken();
  while(1) {
    const token = s.nextToken();
    if(token instanceof EOFToken || token instanceof start.mirror) {
      s.discardToken();
      return block;
    } else {
      block.value.push(consumeAComponentValue(s));
    }
  }
}

function consumeAFunction(s) {
  if(!(s.nextToken() instanceof FunctionToken)) {
    throw new Error("consumeAFunction() called with an invalid token stream state.");
  }
  var func = new Func(s.consumeToken().value);
  while(1) {
    const token = s.nextToken();
    if(token instanceof EOFToken || token instanceof CloseParenToken) {
      s.discardToken();
      return func;
    } else {
      func.value.push(consumeAComponentValue(s));
    }
  }
}

function isValidInContext(construct, context) {
  // Trivial validator, without any special CSS knowledge.

  // All at-rules are valid, who cares.
  if(construct.type == "AT-RULE") return true;

  // Exclude qualified rules that ended up with a semicolon
  // in their prelude.
  // (Can only happen at the top level of a stylesheet.)
  if(construct.type == "QUALIFIED-RULE") {
    for(const val of construct.prelude) {
      if(val.type == "SEMICOLON") return false;
    }
    return true;
  }

  // Exclude properties that ended up with a {}-block
  // in their value, unless they're custom.
  if(construct.type == "DECLARATION") {
    if(construct.name.slice(0, 2) == "--") return true;
    for(const val of construct.value) {
      if(val.type == "BLOCK" && val.name == "{") return false;
    }
    return true;
  }
}

function filterValid(construct, context) {
  if(isValidInContext(construct, context)) return construct;
  return;
}

function normalizeInput(input) {
  if(typeof input == "string")
    return new TokenStream(tokenize(input));
  if(input instanceof TokenStream)
    return input;
  if(input.length !== undefined)
    return new TokenStream(input);
  else throw SyntaxError(input);
}

function parseAStylesheet(s) {
  s = normalizeInput(s);
  var sheet = new Stylesheet();
  sheet.rules = consumeAStylesheetsContents(s);
  return sheet;
}

function parseAStylesheetsContents(s) {
  s = normalizeInput(s);
  return consumeAStylesheetsContents(s);
}

function parseABlocksContents(s) {
  s = normalizeInput(s);
  return consumeABlocksContents(s);
}

function parseARule(s) {
  s = normalizeInput(s);
  let rule;
  s.discardWhitespace();
  if(s.nextToken() instanceof EOFToken) throw SyntaxError();
  if(s.nextToken() instanceof AtKeywordToken) {
    rule = consumeAnAtRule(s);
  } else {
    rule = consumeAQualifiedRule(s);
    if(!rule) throw SyntaxError();
  }
  s.discardWhitespace();
  if(s.nextToken() instanceof EOFToken) return rule;
  throw SyntaxError();
}

function parseADeclaration(s) {
  s = normalizeInput(s);
  s.discardWhitespace();
  const decl = consumeADeclaration(s);
  if(decl) return decl
  throw SyntaxError();
}

function parseAComponentValue(s) {
  s = normalizeInput(s);
  s.discardWhitespace();
  if(s.empty()) throw SyntaxError();
  const val = consumeAComponentValue(s);
  s.discardWhitespace();
  if(s.empty()) return val;
  throw SyntaxError();
}

function parseAListOfComponentValues(s) {
  s = normalizeInput(s);
  return consumeAListOfComponentValues(s);
}

function parseACommaSeparatedListOfComponentValues(s) {
  s = normalizeInput(s);
  const groups = [];
  while(!s.empty()) {
    groups.push(consumeAListOfComponentValues(s, false, CommaToken));
    s.discardToken();
  }
  return groups;
}


class CSSParserRule {
  constructor(type) { this.type = type; }
  toString(indent) {
    return JSON.stringify(this,null,indent);
  }
}

class Stylesheet extends CSSParserRule {
  constructor() {
    super("STYLESHEET");
    this.rules = [];
    return this;
  }
  toJSON() {
    return {
      type: this.type,
      rules: this.rules,
    }
  }
  toSource() {
    return this.rules.map(x=>x.toSource()).join("\n");
  }
}

class AtRule extends CSSParserRule {
  constructor(name) {
    super("AT-RULE");
    this.name = name;
    this.prelude = [];
    this.declarations = null;
    this.rules = null;
    return this;
  }
  toJSON() {
    return {
      type: this.type,
      name: this.name,
      prelude: this.prelude,
      declarations: this.declarations,
      rules: this.rules,
    }
  }
  toSource(indent=0) {
    let s = printIndent(indent) + "@" + escapeIdent(this.name);
    s += this.prelude.map(x=>x.toSource()).join("");
    if(this.declarations == null) {
      s += ";\n";
      return s;
    }
    s += "{\n";
    if(this.declarations.length) {
      s += this.declarations.map(x=>x.toSource(indent+1)).join("\n") + "\n";
    }
    if(this.rules.length) {
      s += this.rules.map(x=>x.toSource(indent+1)).join("\n") + "\n";
    }
    s += printIndent(indent) + "}";
    return s;
  }
}

class QualifiedRule extends CSSParserRule {
  constructor() {
    super("QUALIFIED-RULE");
    this.prelude = [];
    this.declarations = [];
    this.rules = [];
    return this;
  }
  toJSON() {
    return {
      type: this.type,
      prelude: this.prelude,
      declarations: this.declarations,
      rules: this.rules,
    }
  }
  toSource(indent=0) {
    let s = printIndent(indent);
    s += this.prelude.map(x=>x.toSource()).join("");
    s += "{\n";
    if(this.declarations.length) {
      s += this.declarations.map(x=>x.toSource(indent+1)).join("\n") + "\n";
    }
    if(this.rules.length) {
      s += this.rules.map(x=>x.toSource(indent+1)).join("\n") + "\n";
    }
    s += printIndent(indent) + "}";
    return s;
  }
}

class Declaration extends CSSParserRule {
  constructor(name) {
    super("DECLARATION")
    this.name = name;
    this.value = [];
    this.important = false;
    return this;
  }
  toJSON() {
    return {
      type: this.type,
      name: this.name,
      value: this.value,
      important: this.important,
    }
  }
  toSource(indent=0) {
    let s = printIndent(indent) + escapeIdent(this.name) + ": ";
    s += this.value.map(x=>x.toSource()).join("");
    if(this.important) {
      s += "!important";
    }
    s += ";";
    return s;
  }
}

class SimpleBlock extends CSSParserRule {
  constructor(type) {
    super("BLOCK");
    this.name = type;
    this.value = [];
    return this;
  }
  toJSON() {
    return {
      type: this.type,
      name: this.name,
      value: this.value,
    }
  }
  toSource() {
    const mirror = {"{":"}", "[":"]", "(":")"};
    return this.name + this.value.map(x=>x.toSource()).join("") + mirror[this.name];
  }
}

class Func extends CSSParserRule {
  constructor(name) {
    super("FUNCTION");
    this.name = name;
    this.value = [];
    return this;
  }
  toJSON() {
    return {
      type: this.type,
      name: this.name,
      value: this.value,
    }
  }
  toSource() {
    return escapeIdent(this.name) + "(" + this.value.map(x=>x.toSource()).join("") + ")";
  }
}

function printIndent(level) {
  return "\t".repeat(level);
}

return {
  config,
  tokenize,
  IdentToken,
  FunctionToken,
  AtKeywordToken,
  HashToken,
  StringToken,
  BadStringToken,
  URLToken,
  BadURLToken,
  DelimToken,
  NumberToken,
  PercentageToken,
  DimensionToken,
  WhitespaceToken,
  CDOToken,
  CDCToken,
  ColonToken,
  SemicolonToken,
  CommaToken,
  OpenParenToken,
  CloseParenToken,
  OpenSquareToken,
  CloseSquareToken,
  OpenCurlyToken,
  CloseCurlyToken,
  EOFToken,
  CSSParserToken,
  CSSParserRule,
  Stylesheet,
  AtRule,
  QualifiedRule,
  Declaration,
  SimpleBlock,
  Func,
  parseAStylesheet,
  parseAStylesheetsContents,
  parseABlocksContents,
  parseARule,
  parseADeclaration,
  parseAComponentValue,
  parseAListOfComponentValues,
  parseACommaSeparatedListOfComponentValues,
};

}));