/* Tokenizer for JavaScript code */

const tokenizeJavaScript = (function () {
  // Advance the stream until the given character (not preceded by a
  // backslash) is encountered, or the end of the line is reached.
  function nextUntilUnescaped(source, end) {
    let escaped = false;
    while (!source.endOfLine()) {
      const next = source.next();
      if (next == end && !escaped)
        return false;
      escaped = !escaped && next == "\\";
    }
    return escaped;
  }

  // A map of JavaScript's keywords. The a/b/c keyword distinction is
  // very rough, but it gives the parser enough information to parse
  // correct code correctly (we don't care that much how we parse
  // incorrect code). The style information included in these objects
  // is used by the highlighter to pick the correct CSS style for a
  // token.
  const keywords = function () {
    function result(type, style) {
      return {type: type, style: "js-" + style};
    }

    // keywords that take a parenthised expression, and then a
    // statement (if)
    const keywordA = result("keyword a", "keyword");
    // keywords that take just a statement (else)
    const keywordB = result("keyword b", "keyword");
    // keywords that optionally take an expression, and form a
    // statement (return)
    const keywordC = result("keyword c", "keyword");
    const operator = result("operator", "keyword");
    const atom = result("atom", "atom");
    return {
      "if": keywordA,
      "while": keywordA,
      "with": keywordA,
      "else": keywordB,
      "do": keywordB,
      "try": keywordB,
      "finally": keywordB,
      "return": keywordC,
      "break": keywordC,
      "continue": keywordC,
      "new": keywordC,
      "delete": keywordC,
      "throw": keywordC,
      "in": operator,
      "typeof": operator,
      "instanceof": operator,
      "var": result("var", "keyword"),
      "function": result("function", "keyword"),
      "catch": result("catch", "keyword"),
      "for": result("for", "keyword"),
      "switch": result("switch", "keyword"),
      "case": result("case", "keyword"),
      "default": result("default", "keyword"),
      "true": atom,
      "false": atom,
      "null": atom,
      "undefined": atom,
      "NaN": atom,
      "Infinity": atom
    };
  }();

  // Some helper regexps
  const isOperatorChar = /[+\-*&%=<>!?|]/;
  const isHexDigit = /[0-9A-Fa-f]/;
  const isWordChar = /[\w\$_]/;

  // Wrapper around jsToken that helps maintain parser state (whether
  // we are inside of a multi-line comment and whether the next token
  // could be a regular expression).
  function jsTokenState(inside, regexp) {
    return function (source, setState) {
      const newInside = inside;
      const type = jsToken(inside, regexp, source, function (c) {
        newInside = c;
      });
      const newRegexp = type.type == "operator" || type.type == "keyword c" || type.type.match(/^[\[{}\(,;:]$/);
      if (newRegexp != regexp || newInside != inside)
        setState(jsTokenState(newInside, newRegexp));
      return type;
    };
  }

  // The token reader, intended to be used by the tokenizer from
  // tokenize.js (through jsTokenState). Advances the source stream
  // over a token, and returns an object containing the type and style
  // of that token.
  function jsToken(inside, regexp, source, setInside) {
    function readHexNumber() {
      source.next(); // skip the 'x'
      source.nextWhileMatches(isHexDigit);
      return {type: "number", style: "js-atom"};
    }

    function readNumber() {
      source.nextWhileMatches(/[0-9]/);
      if (source.equals(".")) {
        source.next();
        source.nextWhileMatches(/[0-9]/);
      }
      if (source.equals("e") || source.equals("E")) {
        source.next();
        if (source.equals("-"))
          source.next();
        source.nextWhileMatches(/[0-9]/);
      }
      return {type: "number", style: "js-atom"};
    }

    // Read a word, look it up in keywords. If not found, it is a
    // variable, otherwise it is a keyword of the type found.
    function readWord() {
      source.nextWhileMatches(isWordChar);
      const word = source.get();
      const known = keywords.hasOwnProperty(word) && keywords.propertyIsEnumerable(word) && keywords[word];
      return known ? {type: known.type, style: known.style, content: word} :
          {type: "variable", style: "js-variable", content: word};
    }

    function readRegexp() {
      nextUntilUnescaped(source, "/");
      source.nextWhileMatches(/[gi]/);
      return {type: "regexp", style: "js-string"};
    }

    // Mutli-line comments are tricky. We want to return the newlines
    // embedded in them as regular newline tokens, and then continue
    // returning a comment token for every line of the comment. So
    // some state has to be saved (inside) to indicate whether we are
    // inside a /* */ sequence.
    function readMultilineComment(start) {
      let newInside = "/*";
      let maybeEnd = (start == "*");
      while (true) {
        if (source.endOfLine())
          break;
        const next = source.next();
        if (next == "/" && maybeEnd) {
          newInside = null;
          break;
        }
        maybeEnd = (next == "*");
      }
      setInside(newInside);
      return {type: "comment", style: "js-comment"};
    }

    function readOperator() {
      source.nextWhileMatches(isOperatorChar);
      return {type: "operator", style: "js-operator"};
    }

    function readString(quote) {
      const endBackSlash = nextUntilUnescaped(source, quote);
      setInside(endBackSlash ? quote : null);
      return {type: "string", style: "js-string"};
    }

    // Fetch the next token. Dispatches on first character in the
    // stream, or first two characters when the first is a slash.
    if (inside == "\"" || inside == "'")
      return readString(inside);
    const ch = source.next();
    if (inside == "/*")
      return readMultilineComment(ch);
    else if (ch == "\"" || ch == "'")
      return readString(ch);
    // with punctuation, the type of the token is the symbol itself
    else if (/[\[\]{}\(\),;\:\.]/.test(ch))
      return {type: ch, style: "js-punctuation"};
    else if (ch == "0" && (source.equals("x") || source.equals("X")))
      return readHexNumber();
    else if (/[0-9]/.test(ch))
      return readNumber();
    else if (ch == "/") {
      if (source.equals("*")) {
        source.next();
        return readMultilineComment(ch);
      } else if (source.equals("/")) {
        nextUntilUnescaped(source, null);
        return {type: "comment", style: "js-comment"};
      } else if (regexp)
        return readRegexp();
      else
        return readOperator();
    } else if (isOperatorChar.test(ch))
      return readOperator();
    else
      return readWord();
  }

  // The external interface to the tokenizer.
  return function (source, startState) {
    return tokenizer(source, startState || jsTokenState(false, true));
  };
})();
