/**
 * @prototype Hash
 * This prototype contains methods to manipulate the hash of the web page
 */
function Hash() {}

/**
 * get an object value with all parameters in the hash
 * @return {Object} query    object containing key/values
 */
Hash.prototype.getQuery = function () {
    var hash = window.location.hash.substring(1); // skip the # character
    var params = hash.split('&');
    var query = {};
    for (var i = 0, iMax = params.length; i < iMax; i++) {
        var keyvalue = params[i].split('=');
        if (keyvalue.length == 2) {
            var key = decodeURIComponent(keyvalue[0]);
            var value = decodeURIComponent(keyvalue[1]);
            query[key] = value;
        }
    }
    return query;
};

/**
 * Register a callback function which will be called when the hash of the web
 * page changes.
 * @param {String} key
 * @param {function} callback   Will be called with the new value as parameter
 */
Hash.prototype.onChange = function (key, callback) {
    this.prevHash = '';
    var me = this;
    if (!me.callbacks) {
        me.callbacks = [];
    }
    me.callbacks.push({
        'key': key,
        'value': undefined,
        'callback': callback
    });

    function checkForChanges() {
        for (var i = 0; i < me.callbacks.length; i++) {
            var obj = me.callbacks[i];
            var value = me.getValue(obj.key);
            var changed = (value !== obj.value);
            obj.value = value;
            if (changed) {
                obj.callback(value);
            }
        }
    }

    // source: http://stackoverflow.com/questions/2161906/handle-url-anchor-change-event-in-js
    if ('onhashchange' in window) {
        window.onhashchange = function () {
            checkForChanges();
        }
    }
    else {
        // onhashchange event not supported
        me.prevHash = window.location.hash;
        window.setInterval(function () {
            var hash = window.location.hash;
            if (hash != me.prevHash) {
                me.prevHash = hash;
                checkForChanges();
            }
        }, 500);
    }
};


/**
 * Set hash parameters
 * @param {Object} query    object with strings
 */
Hash.prototype.setQuery = function (query) {
    var hash = '';

    for (var key in query) {
        if (query.hasOwnProperty(key)) {
            var value = query[key];
            if (value != undefined) {
                if (hash.length) {
                    hash += '&';
                }
                hash += encodeURIComponent(key);
                hash += '=';
                hash += encodeURIComponent(query[key]);
            }
        }
    }

    window.location.hash = (hash.length ? ('#' + hash) : '');
};


/**
 * Retrieve a parameter value from the hash
 * @param {String} key
 * @return {String | undefined} value   undefined when the value is not found
 */
Hash.prototype.getValue = function (key) {
    var query = this.getQuery();
    return query[key];
};

/**
 * Set an hash parameter
 * @param {String} key
 * @param {String} value
 */
Hash.prototype.setValue = function (key, value) {
    var query = this.getQuery();
    query[key] = value;
    this.setQuery(query);
};

/**
 * Remove an hash parameter
 * @param {String} key
 */
Hash.prototype.removeValue = function (key) {
    var query = this.getQuery();
    if (query[key]) {
        delete query[key];
        this.setQuery(query);
    }
};