var OPERATORS = {
    'null':function(self){return null;},
    'true':function(self){return true;},
    'false':function(self){return false;},
    $undefined:noop,
    '+':function(self, a,b){return (isDefined(a)?a:0)+(isDefined(b)?b:0);},
    '-':function(self, a,b){return (isDefined(a)?a:0)-(isDefined(b)?b:0);},
    '*':function(self, a,b){return a*b;},
    '/':function(self, a,b){return a/b;},
    '%':function(self, a,b){return a%b;},
    '^':function(self, a,b){return a^b;},
    '=':noop,
    '==':function(self, a,b){return a==b;},
    '!=':function(self, a,b){return a!=b;},
    '<':function(self, a,b){return a<b;},
    '>':function(self, a,b){return a>b;},
    '<=':function(self, a,b){return a<=b;},
    '>=':function(self, a,b){return a>=b;},
    '&&':function(self, a,b){return a&&b;},
    '||':function(self, a,b){return a||b;},
    '&':function(self, a,b){return a&b;},
//    '|':function(self, a,b){return a|b;},
    '|':function(self, a,b){return b(self, a);},
    '!':function(self, a){return !a;}
};
var ESCAPE = {"n":"\n", "f":"\f", "r":"\r", "t":"\t", "v":"\v", "'":"'", '"':'"'};

function lex(text, parseStringsForObjects){
  var dateParseLength = parseStringsForObjects ? DATE_ISOSTRING_LN : -1,
      tokens = [],
      token,
      index = 0,
      json = [],
      ch,
      lastCh = ':'; // can start regexp

  while (index < text.length) {
    ch = text.charAt(index);
    if (is('"\'')) {
      readString(ch);
    } else if (isNumber(ch) || is('.') && isNumber(peek())) {
      readNumber();
    } else if (isIdent(ch)) {
      readIdent();
      // identifiers can only be if the preceding char was a { or ,
      if (was('{,') && json[0]=='{' &&
         (token=tokens[tokens.length-1])) {
        token.json = token.text.indexOf('.') == -1;
      }
    } else if (is('(){}[].,;:')) {
      tokens.push({
        index:index,
        text:ch,
        json:(was(':[,') && is('{[')) || is('}]:,')
      });
      if (is('{[')) json.unshift(ch);
      if (is('}]')) json.shift();
      index++;
    } else if (isWhitespace(ch)) {
      index++;
      continue;
    } else {
      var ch2 = ch + peek(),
          fn = OPERATORS[ch],
          fn2 = OPERATORS[ch2];
      if (fn2) {
        tokens.push({index:index, text:ch2, fn:fn2});
        index += 2;
      } else if (fn) {
        tokens.push({index:index, text:ch, fn:fn, json: was('[,:') && is('+-')});
        index += 1;
      } else {
        throwError("Unexpected next character ", index, index+1);
      }
    }
    lastCh = ch;
  }
  return tokens;

  function is(chars) {
    return chars.indexOf(ch) != -1;
  }

  function was(chars) {
    return chars.indexOf(lastCh) != -1;
  }

  function peek() {
    return index + 1 < text.length ? text.charAt(index + 1) : false;
  }
  function isNumber(ch) {
    return '0' <= ch && ch <= '9';
  }
  function isWhitespace(ch) {
    return ch == ' ' || ch == '\r' || ch == '\t' ||
           ch == '\n' || ch == '\v' || ch == '\u00A0'; // IE treats non-breaking space as \u00A0
  }
  function isIdent(ch) {
    return 'a' <= ch && ch <= 'z' ||
           'A' <= ch && ch <= 'Z' ||
           '_' == ch || ch == '$';
  }
  function isExpOperator(ch) {
    return ch == '-' || ch == '+' || isNumber(ch);
  }

  function throwError(error, start, end) {
    end = end || index;
    throw Error("Lexer Error: " + error + " at column" +
        (isDefined(start)
            ? "s " + start +  "-" + index + " [" + text.substring(start, end) + "]"
            : " " + end) +
        " in expression [" + text + "].");
  }

  function readNumber() {
    var number = "";
    var start = index;
    while (index < text.length) {
      var ch = lowercase(text.charAt(index));
      if (ch == '.' || isNumber(ch)) {
        number += ch;
      } else {
        var peekCh = peek();
        if (ch == 'e' && isExpOperator(peekCh)) {
          number += ch;
        } else if (isExpOperator(ch) &&
            peekCh && isNumber(peekCh) &&
            number.charAt(number.length - 1) == 'e') {
          number += ch;
        } else if (isExpOperator(ch) &&
            (!peekCh || !isNumber(peekCh)) &&
            number.charAt(number.length - 1) == 'e') {
          throwError('Invalid exponent');
        } else {
          break;
        }
      }
      index++;
    }
    number = 1 * number;
    tokens.push({index:start, text:number, json:true,
      fn:function(){return number;}});
  }
  function readIdent() {
    var ident = "";
    var start = index;
    var fn;
    while (index < text.length) {
      var ch = text.charAt(index);
      if (ch == '.' || isIdent(ch) || isNumber(ch)) {
        ident += ch;
      } else {
        break;
      }
      index++;
    }
    fn = OPERATORS[ident];
    tokens.push({
      index:start,
      text:ident,
      json: fn,
      fn:fn||extend(getterFn(ident), {
        assign:function(self, value){
          return setter(self, ident, value);
        }
      })
    });
  }

  function readString(quote) {
    var start = index;
    index++;
    var string = "";
    var rawString = quote;
    var escape = false;
    while (index < text.length) {
      var ch = text.charAt(index);
      rawString += ch;
      if (escape) {
        if (ch == 'u') {
          var hex = text.substring(index + 1, index + 5);
          if (!hex.match(/[\da-f]{4}/i))
            throwError( "Invalid unicode escape [\\u" + hex + "]");
          index += 4;
          string += String.fromCharCode(parseInt(hex, 16));
        } else {
          var rep = ESCAPE[ch];
          if (rep) {
            string += rep;
          } else {
            string += ch;
          }
        }
        escape = false;
      } else if (ch == '\\') {
        escape = true;
      } else if (ch == quote) {
        index++;
        tokens.push({index:start, text:rawString, string:string, json:true,
          fn:function(){
            return (string.length == dateParseLength)
              ? angular['String']['toDate'](string)
              : string;
          }});
        return;
      } else {
        string += ch;
      }
      index++;
    }
    throwError("Unterminated quote", start);
  }
}

/////////////////////////////////////////

function parser(text, json){
  var ZERO = valueFn(0),
      tokens = lex(text, json),
      assignment = _assignment,
      assignable = logicalOR,
      functionCall = _functionCall,
      fieldAccess = _fieldAccess,
      objectIndex = _objectIndex,
      filterChain = _filterChain,
      functionIdent = _functionIdent,
      pipeFunction = _pipeFunction;
  if(json){
    // The extra level of aliasing is here, just in case the lexer misses something, so that
    // we prevent any accidental execution in JSON.
    assignment = logicalOR;
    functionCall =
      fieldAccess =
      objectIndex =
      assignable =
      filterChain =
      functionIdent =
      pipeFunction =
        function (){ throwError("is not valid json", {text:text, index:0}); };
  }
  return {
      assertAllConsumed: assertAllConsumed,
      assignable: assignable,
      primary: primary,
      statements: statements,
      validator: validator,
      formatter: formatter,
      filter: filter,
      //TODO: delete me, since having watch in UI is logic in UI. (leftover form getangular)
      watch: watch
  };

  ///////////////////////////////////
  function throwError(msg, token) {
    throw Error("Parse Error: Token '" + token.text +
      "' " + msg + " at column " +
      (token.index + 1) + " of expression [" +
      text + "] starting at [" + text.substring(token.index) + "].");
  }

  function peekToken() {
    if (tokens.length === 0)
      throw Error("Unexpected end of expression: " + text);
    return tokens[0];
  }

  function peek(e1, e2, e3, e4) {
    if (tokens.length > 0) {
      var token = tokens[0];
      var t = token.text;
      if (t==e1 || t==e2 || t==e3 || t==e4 ||
          (!e1 && !e2 && !e3 && !e4)) {
        return token;
      }
    }
    return false;
  }

  function expect(e1, e2, e3, e4){
    var token = peek(e1, e2, e3, e4);
    if (token) {
      if (json && !token.json) {
        index = token.index;
        throwError("is not valid json", token);
      }
      tokens.shift();
      this.currentToken = token;
      return token;
    }
    return false;
  }

  function consume(e1){
    if (!expect(e1)) {
      throwError("is unexpected, expecting [" + e1 + "]", peek());
    }
  }

  function unaryFn(fn, right) {
    return function(self) {
      return fn(self, right(self));
    };
  }

  function binaryFn(left, fn, right) {
    return function(self) {
      return fn(self, left(self), right(self));
    };
  }

  function hasTokens () {
    return tokens.length > 0;
  }

  function assertAllConsumed(){
    if (tokens.length !== 0) {
      throwError("is extra token not part of expression", tokens[0]);
    }
  }

  function statements(){
    var statements = [];
    while(true) {
      if (tokens.length > 0 && !peek('}', ')', ';', ']'))
        statements.push(filterChain());
      if (!expect(';')) {
        return function (self){
          var value;
          for ( var i = 0; i < statements.length; i++) {
            var statement = statements[i];
            if (statement)
              value = statement(self);
          }
          return value;
        };
      }
    }
  }

  function _filterChain(){
    var left = expression();
    var token;
    while(true) {
      if ((token = expect('|'))) {
        left = binaryFn(left, token.fn, filter());
      } else {
        return left;
      }
    }
  }

  function filter(){
    return pipeFunction(angularFilter);
  }

  function validator(){
    return pipeFunction(angularValidator);
  }

  function formatter(){
    var token = expect();
    var formatter = angularFormatter[token.text];
    var argFns = [];
    if (!formatter) throwError('is not a valid formatter.', token);
    while(true) {
      if ((token = expect(':'))) {
        argFns.push(expression());
      } else {
        return valueFn({
          format:invokeFn(formatter.format),
          parse:invokeFn(formatter.parse)
        });
      }
    }
    function invokeFn(fn){
      return function(self, input){
        var args = [input];
        for ( var i = 0; i < argFns.length; i++) {
          args.push(argFns[i](self));
        }
        return fn.apply(self, args);
      };
    }
  }

  function _pipeFunction(fnScope){
    var fn = functionIdent(fnScope);
    var argsFn = [];
    var token;
    while(true) {
      if ((token = expect(':'))) {
        argsFn.push(expression());
      } else {
        var fnInvoke = function(self, input){
          var args = [input];
          for ( var i = 0; i < argsFn.length; i++) {
            args.push(argsFn[i](self));
          }
          return fn.apply(self, args);
        };
        return function(){
          return fnInvoke;
        };
      }
    }
  }

  function expression(){
    return assignment();
  }

  function _assignment(){
    var left = logicalOR();
    var right;
    var token;
    if (token = expect('=')) {
      if (!left.assign) {
        throwError("implies assignment but [" +
          text.substring(0, token.index) + "] can not be assigned to", token);
      }
      right = logicalOR();
      return function(self){
        return left.assign(self, right(self));
      };
    } else {
      return left;
    }
  }

  function logicalOR(){
    var left = logicalAND();
    var token;
    while(true) {
      if ((token = expect('||'))) {
        left = binaryFn(left, token.fn, logicalAND());
      } else {
        return left;
      }
    }
  }

  function logicalAND(){
    var left = equality();
    var token;
    if ((token = expect('&&'))) {
      left = binaryFn(left, token.fn, logicalAND());
    }
    return left;
  }

  function equality(){
    var left = relational();
    var token;
    if ((token = expect('==','!='))) {
      left = binaryFn(left, token.fn, equality());
    }
    return left;
  }

  function relational(){
    var left = additive();
    var token;
    if (token = expect('<', '>', '<=', '>=')) {
      left = binaryFn(left, token.fn, relational());
    }
    return left;
  }

  function additive(){
    var left = multiplicative();
    var token;
    while(token = expect('+','-')) {
      left = binaryFn(left, token.fn, multiplicative());
    }
    return left;
  }

  function multiplicative(){
    var left = unary();
    var token;
    while(token = expect('*','/','%')) {
      left = binaryFn(left, token.fn, unary());
    }
    return left;
  }

  function unary(){
    var token;
    if (expect('+')) {
      return primary();
    } else if (token = expect('-')) {
      return binaryFn(ZERO, token.fn, unary());
    } else if (token = expect('!')) {
      return unaryFn(token.fn, unary());
    } else {
      return primary();
    }
  }

  function _functionIdent(fnScope) {
    var token = expect();
    var element = token.text.split('.');
    var instance = fnScope;
    var key;
    for ( var i = 0; i < element.length; i++) {
      key = element[i];
      if (instance)
        instance = instance[key];
    }
    if (typeof instance != $function) {
      throwError("should be a function", token);
    }
    return instance;
  }

  function primary() {
    var primary;
    if (expect('(')) {
      var expression = filterChain();
      consume(')');
      primary = expression;
    } else if (expect('[')) {
      primary = arrayDeclaration();
    } else if (expect('{')) {
      primary = object();
    } else {
      var token = expect();
      primary = token.fn;
      if (!primary) {
        throwError("not a primary expression", token);
      }
    }
    var next;
    while (next = expect('(', '[', '.')) {
      if (next.text === '(') {
        primary = functionCall(primary);
      } else if (next.text === '[') {
        primary = objectIndex(primary);
      } else if (next.text === '.') {
        primary = fieldAccess(primary);
      } else {
        throwError("IMPOSSIBLE");
      }
    }
    return primary;
  }

  function _fieldAccess(object) {
    var field = expect().text;
    var getter = getterFn(field);
    return extend(function (self){
      return getter(object(self));
    }, {
      assign:function(self, value){
        return setter(object(self), field, value);
      }
    });
  }

  function _objectIndex(obj) {
    var indexFn = expression();
    consume(']');
    return extend(
      function (self){
        var o = obj(self);
        var i = indexFn(self);
        return (o) ? o[i] : undefined;
      }, {
        assign:function(self, value){
          return obj(self)[indexFn(self)] = value;
        }
      });
  }

  function _functionCall(fn) {
    var argsFn = [];
    if (peekToken().text != ')') {
      do {
        argsFn.push(expression());
      } while (expect(','));
    }
    consume(')');
    return function (self){
      var args = [];
      for ( var i = 0; i < argsFn.length; i++) {
        args.push(argsFn[i](self));
      }
      var fnPtr = fn(self) || noop;
      // IE stupidity!
      return fnPtr.apply
          ? fnPtr.apply(self, args)
          : fnPtr(args[0], args[1], args[2], args[3], args[4]);
    };
  }

  // This is used with json array declaration
  function arrayDeclaration () {
    var elementFns = [];
    if (peekToken().text != ']') {
      do {
        elementFns.push(expression());
      } while (expect(','));
    }
    consume(']');
    return function (self){
      var array = [];
      for ( var i = 0; i < elementFns.length; i++) {
        array.push(elementFns[i](self));
      }
      return array;
    };
  }

  function object () {
    var keyValues = [];
    if (peekToken().text != '}') {
      do {
        var token = expect(),
        key = token.string || token.text;
        consume(":");
        var value = expression();
        keyValues.push({key:key, value:value});
      } while (expect(','));
    }
    consume('}');
    return function (self){
      var object = {};
      for ( var i = 0; i < keyValues.length; i++) {
        var keyValue = keyValues[i];
        var value = keyValue.value(self);
        object[keyValue.key] = value;
      }
      return object;
    };
  }

  //TODO: delete me, since having watch in UI is logic in UI. (leftover form getangular)
  function watch () {
    var decl = [];
    while(hasTokens()) {
      decl.push(watchDecl());
      if (!expect(';')) {
        assertAllConsumed();
      }
    }
    assertAllConsumed();
    return function (self){
      for ( var i = 0; i < decl.length; i++) {
        var d = decl[i](self);
        self.addListener(d.name, d.fn);
      }
    };
  }

  function watchDecl () {
    var anchorName = expect().text;
    consume(":");
    var expressionFn;
    if (peekToken().text == '{') {
      consume("{");
      expressionFn = statements();
      consume("}");
    } else {
      expressionFn = expression();
    }
    return function(self) {
      return {name:anchorName, fn:expressionFn};
    };
  }
}