/**
 * <p>The JSON module adds support for serializing JavaScript objects into
 * JSON strings and parsing JavaScript objects from strings in JSON format.</p>
 *
 * <p>The JSON namespace is added to your YUI instance including static methods
 * Y.JSON.parse(..) and Y.JSON.stringify(..).</p>
 *
 * <p>The functionality and method signatures follow the ECMAScript 5
 * specification.  In browsers with native JSON support, the native
 * implementation is used.</p>
 *
 * <p>The <code>json</code> module is a rollup of <code>json-parse</code> and
 * <code>json-stringify</code>.</p>
 *
 * <p>As their names suggest, <code>json-parse</code> adds support for parsing
 * JSON data (Y.JSON.parse) and <code>json-stringify</code> for serializing
 * JavaScript data into JSON strings (Y.JSON.stringify).  You may choose to
 * include either of the submodules individually if you don't need the
 * complementary functionality, or include the rollup for both.</p>
 *
 * @module json
 * @main json
 * @class JSON
 * @static
 */

/**
 * Provides Y.JSON.parse method to accept JSON strings and return native
 * JavaScript objects.
 *
 * @module json
 * @submodule json-parse
 * @for JSON
 * @static
 */


    /**
     * Replace certain Unicode characters that JavaScript may handle incorrectly
     * during eval--either by deleting them or treating them as line
     * endings--with escape sequences.
     * IMPORTANT NOTE: This regex will be used to modify the input if a match is
     * found.
     *
     * @property _UNICODE_EXCEPTIONS
     * @type {RegExp}
     * @private
     */
var _UNICODE_EXCEPTIONS = /[\u0000\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,


    /**
     * First step in the safety evaluation.  Regex used to replace all escape
     * sequences (i.e. "\\", etc) with '@' characters (a non-JSON character).
     *
     * @property _ESCAPES
     * @type {RegExp}
     * @private
     */
    _ESCAPES = /\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g,

    /**
     * Second step in the safety evaluation.  Regex used to replace all simple
     * values with ']' characters.
     *
     * @property _VALUES
     * @type {RegExp}
     * @private
     */
    _VALUES  = /"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g,

    /**
     * Third step in the safety evaluation.  Regex used to remove all open
     * square brackets following a colon, comma, or at the beginning of the
     * string.
     *
     * @property _BRACKETS
     * @type {RegExp}
     * @private
     */
    _BRACKETS = /(?:^|:|,)(?:\s*\[)+/g,

    /**
     * Final step in the safety evaluation.  Regex used to test the string left
     * after all previous replacements for invalid characters.
     *
     * @property _UNSAFE
     * @type {RegExp}
     * @private
     */
    _UNSAFE = /[^\],:{}\s]/,

    /**
     * Replaces specific unicode characters with their appropriate \unnnn
     * format. Some browsers ignore certain characters during eval.
     *
     * @method escapeException
     * @param c {String} Unicode character
     * @return {String} the \unnnn escapement of the character
     * @private
     */
    _escapeException = function (c) {
        return '\\u'+('0000'+(+(c.charCodeAt(0))).toString(16)).slice(-4);
    },

    /**
     * Traverses nested objects, applying a reviver function to each (key,value)
     * from the scope if the key:value's containing object.  The value returned
     * from the function will replace the original value in the key:value pair.
     * If the value returned is undefined, the key will be omitted from the
     * returned object.
     *
     * @method _revive
     * @param data {MIXED} Any JavaScript data
     * @param reviver {Function} filter or mutation function
     * @return {MIXED} The results of the filtered data
     * @private
     */
    _revive = function (data, reviver) {
        var walk = function (o,key) {
            var k,v,value = o[key];
            if (value && typeof value === 'object') {
                for (k in value) {
                    if (value.hasOwnProperty(k)) {
                        v = walk(value, k);
                        if (v === undefined) {
                            delete value[k];
                        } else {
                            value[k] = v;
                        }
                    }
                }
            }
            return reviver.call(o,key,value);
        };

        return typeof reviver === 'function' ? walk({'':data},'') : data;
    };

/**
 * Parse a JSON string, returning the native JavaScript representation.
 *
 * @param s {string} JSON string data
 * @param reviver {function} (optional) function(k,v) passed each key value
 *          pair of object literals, allowing pruning or altering values
 * @return {MIXED} the native JavaScript representation of the JSON string
 * @throws SyntaxError
 * @method parse
 * @static
 */
// JavaScript implementation in lieu of native browser support.  Based on
// the json2.js library from http://json.org
Y.JSON.parse = function (s,reviver) {
    if (typeof s !== 'string') {
        s += '';
    }

    // Replace certain Unicode characters that are otherwise handled
    // incorrectly by some browser implementations.
    // NOTE: This modifies the input if such characters are found!
    s = s.replace(_UNICODE_EXCEPTIONS, _escapeException);

    // Test for any remaining invalid characters
    if (!_UNSAFE.test(s.replace(_ESCAPES,'@').
                        replace(_VALUES,']').
                        replace(_BRACKETS,''))) {

        // Eval the text into a JavaScript data structure, apply any
        // reviver function, and return
        return _revive(eval('(' + s + ')'), reviver);
    }

    throw new SyntaxError('JSON.parse');
};

// Property available for testing if the implementation being used
// is native or a shim
Y.JSON.parse.isShim = true;
