ko.expressionRewriting = (function () {
    var javaScriptReservedWords = ["true", "false", "null", "undefined"];

    // Matches something that can be assigned to--either an isolated identifier or something ending with a property accessor
    // This is designed to be simple and avoid false negatives, but could produce false positives (e.g., a+b.c).
    // This also will not properly handle nested brackets (e.g., obj1[obj2['prop']]; see #911).
    var javaScriptAssignmentTarget = /^(?:[$_a-z][$\w]*|(.+)(\.\s*[$_a-z][$\w]*|\[.+\]))$/i;

    function getWriteableValue(expression) {
        if (ko.utils.arrayIndexOf(javaScriptReservedWords, expression) >= 0)
            return false;
        var match = expression.match(javaScriptAssignmentTarget);
        return match === null ? false : match[1] ? ('Object(' + match[1] + ')' + match[2]) : expression;
    }

    // The following regular expressions will be used to split an object-literal string into tokens

        // These two match strings, either with double quotes or single quotes
    var stringDouble = '"(?:[^"\\\\]|\\\\.)*"',
        stringSingle = "'(?:[^'\\\\]|\\\\.)*'",
        // Matches a regular expression (text enclosed by slashes), but will also match sets of divisions
        // as a regular expression (this is handled by the parsing loop below).
        stringRegexp = '/(?:[^/\\\\]|\\\\.)*/\w*',
        // These characters have special meaning to the parser and must not appear in the middle of a
        // token, except as part of a string.
        specials = ',"\'{}()/:[\\]',
        // Match text (at least two characters) that does not contain any of the above special characters,
        // although some of the special characters are allowed to start it (all but the colon and comma).
        // The text can contain spaces, but leading or trailing spaces are skipped.
        everyThingElse = '[^\\s:,/][^' + specials + ']*[^\\s' + specials + ']',
        // Match any non-space character not matched already. This will match colons and commas, since they're
        // not matched by "everyThingElse", but will also match any other single character that wasn't already
        // matched (for example: in "a: 1, b: 2", each of the non-space characters will be matched by oneNotSpace).
        oneNotSpace = '[^\\s]',

        // Create the actual regular expression by or-ing the above strings. The order is important.
        bindingToken = RegExp(stringDouble + '|' + stringSingle + '|' + stringRegexp + '|' + everyThingElse + '|' + oneNotSpace, 'g'),

        // Match end of previous token to determine whether a slash is a division or regex.
        divisionLookBehind = /[\])"'A-Za-z0-9_$]+$/,
        keywordRegexLookBehind = {'in':1,'return':1,'typeof':1};

    function parseObjectLiteral(objectLiteralString) {
        // Trim leading and trailing spaces from the string
        var str = ko.utils.stringTrim(objectLiteralString);

        // Trim braces '{' surrounding the whole object literal
        if (str.charCodeAt(0) === 123) str = str.slice(1, -1);

        // Split into tokens
        var result = [], toks = str.match(bindingToken), key, values, depth = 0;

        if (toks) {
            // Append a comma so that we don't need a separate code block to deal with the last item
            toks.push(',');

            for (var i = 0, tok; tok = toks[i]; ++i) {
                var c = tok.charCodeAt(0);
                // A comma signals the end of a key/value pair if depth is zero
                if (c === 44) { // ","
                    if (depth <= 0) {
                        if (key)
                            result.push(values ? {key: key, value: values.join('')} : {'unknown': key});
                        key = values = depth = 0;
                        continue;
                    }
                // Simply skip the colon that separates the name and value
                } else if (c === 58) { // ":"
                    if (!values)
                        continue;
                // A set of slashes is initially matched as a regular expression, but could be division
                } else if (c === 47 && i && tok.length > 1) {  // "/"
                    // Look at the end of the previous token to determine if the slash is actually division
                    var match = toks[i-1].match(divisionLookBehind);
                    if (match && !keywordRegexLookBehind[match[0]]) {
                        // The slash is actually a division punctuator; re-parse the remainder of the string (not including the slash)
                        str = str.substr(str.indexOf(tok) + 1);
                        toks = str.match(bindingToken);
                        toks.push(',');
                        i = -1;
                        // Continue with just the slash
                        tok = '/';
                    }
                // Increment depth for parentheses, braces, and brackets so that interior commas are ignored
                } else if (c === 40 || c === 123 || c === 91) { // '(', '{', '['
                    ++depth;
                } else if (c === 41 || c === 125 || c === 93) { // ')', '}', ']'
                    --depth;
                // The key must be a single token; if it's a string, trim the quotes
                } else if (!key && !values) {
                    key = (c === 34 || c === 39) /* '"', "'" */ ? tok.slice(1, -1) : tok;
                    continue;
                }
                if (values)
                    values.push(tok);
                else
                    values = [tok];
            }
        }
        return result;
    }

    // Two-way bindings include a write function that allow the handler to update the value even if it's not an observable.
    var twoWayBindings = {};

    function preProcessBindings(bindingsStringOrKeyValueArray, bindingOptions) {
        bindingOptions = bindingOptions || {};

        function processKeyValue(key, val) {
            var writableVal;
            function callPreprocessHook(obj) {
                return (obj && obj['preprocess']) ? (val = obj['preprocess'](val, key, processKeyValue)) : true;
            }
            if (!bindingParams) {
                if (!callPreprocessHook(ko['getBindingHandler'](key)))
                    return;

                if (twoWayBindings[key] && (writableVal = getWriteableValue(val))) {
                    // For two-way bindings, provide a write method in case the value
                    // isn't a writable observable.
                    propertyAccessorResultStrings.push("'" + key + "':function(_z){" + writableVal + "=_z}");
                }
            }
            // Values are wrapped in a function so that each value can be accessed independently
            if (makeValueAccessors) {
                val = 'function(){return ' + val + ' }';
            }
            resultStrings.push("'" + key + "':" + val);
        }

        var resultStrings = [],
            propertyAccessorResultStrings = [],
            makeValueAccessors = bindingOptions['valueAccessors'],
            bindingParams = bindingOptions['bindingParams'],
            keyValueArray = typeof bindingsStringOrKeyValueArray === "string" ?
                parseObjectLiteral(bindingsStringOrKeyValueArray) : bindingsStringOrKeyValueArray;

        ko.utils.arrayForEach(keyValueArray, function(keyValue) {
            processKeyValue(keyValue.key || keyValue['unknown'], keyValue.value);
        });

        if (propertyAccessorResultStrings.length)
            processKeyValue('_ko_property_writers', "{" + propertyAccessorResultStrings.join(",") + " }");

        return resultStrings.join(",");
    }

    return {
        bindingRewriteValidators: [],

        twoWayBindings: twoWayBindings,

        parseObjectLiteral: parseObjectLiteral,

        preProcessBindings: preProcessBindings,

        keyValueArrayContainsKey: function(keyValueArray, key) {
            for (var i = 0; i < keyValueArray.length; i++)
                if (keyValueArray[i]['key'] == key)
                    return true;
            return false;
        },

        // Internal, private KO utility for updating model properties from within bindings
        // property:            If the property being updated is (or might be) an observable, pass it here
        //                      If it turns out to be a writable observable, it will be written to directly
        // allBindings:         An object with a get method to retrieve bindings in the current execution context.
        //                      This will be searched for a '_ko_property_writers' property in case you're writing to a non-observable
        // key:                 The key identifying the property to be written. Example: for { hasFocus: myValue }, write to 'myValue' by specifying the key 'hasFocus'
        // value:               The value to be written
        // checkIfDifferent:    If true, and if the property being written is a writable observable, the value will only be written if
        //                      it is !== existing value on that writable observable
        writeValueToProperty: function(property, allBindings, key, value, checkIfDifferent) {
            if (!property || !ko.isObservable(property)) {
                var propWriters = allBindings.get('_ko_property_writers');
                if (propWriters && propWriters[key])
                    propWriters[key](value);
            } else if (ko.isWriteableObservable(property) && (!checkIfDifferent || property.peek() !== value)) {
                property(value);
            }
        }
    };
})();

ko.exportSymbol('expressionRewriting', ko.expressionRewriting);
ko.exportSymbol('expressionRewriting.bindingRewriteValidators', ko.expressionRewriting.bindingRewriteValidators);
ko.exportSymbol('expressionRewriting.parseObjectLiteral', ko.expressionRewriting.parseObjectLiteral);
ko.exportSymbol('expressionRewriting.preProcessBindings', ko.expressionRewriting.preProcessBindings);

// Making bindings explicitly declare themselves as "two way" isn't ideal in the long term (it would be better if
// all bindings could use an official 'property writer' API without needing to declare that they might). However,
// since this is not, and has never been, a public API (_ko_property_writers was never documented), it's acceptable
// as an internal implementation detail in the short term.
// For those developers who rely on _ko_property_writers in their custom bindings, we expose _twoWayBindings as an
// undocumented feature that makes it relatively easy to upgrade to KO 3.0. However, this is still not an official
// public API, and we reserve the right to remove it at any time if we create a real public property writers API.
ko.exportSymbol('expressionRewriting._twoWayBindings', ko.expressionRewriting.twoWayBindings);

// For backward compatibility, define the following aliases. (Previously, these function names were misleading because
// they referred to JSON specifically, even though they actually work with arbitrary JavaScript object literal expressions.)
ko.exportSymbol('jsonExpressionRewriting', ko.expressionRewriting);
ko.exportSymbol('jsonExpressionRewriting.insertPropertyAccessorsIntoJson', ko.expressionRewriting.preProcessBindings);
