var LinkedSelect = function() { this.initialize.apply(this, arguments) };
LinkedSelect.prototype = {
    initialize: function(master, slave, options) {
        this.master = (typeof master == 'string') ? _$(master).el[0] : master;
        this.slave = (typeof slave == 'string') ? _$(slave).el[0] : slave;
        this.options = options || {};
        this.actionURL = this.options.url;
        
        var self = this;
        YAHOO.util.Event.addListener(this.master, 'change', function() {
            self.updateSlave();
        });
        
        if (this.options.updateNow) this.updateSlave();
    },
    
    updateSlave: function() {
        if (!this.actionURL) throw new Error('No update URL specified for LinkedSelect');
        
        var list = this.master, data = {};
        data[list.name] = list.value;
        if (this.options.alsoPasses)
            this.options.alsoPasses.forEach(function(field) {
                data[field.name] = field.value;
            });
        
        var query = '';
        for (var key in data)
            query += (query ? '&' : '') + encodeURIComponent(key) +
                '=' + encodeURIComponent(data[key]);
        
        YAHOO.util.Connect.asyncRequest('GET', this.actionURL + '?' + query, {
            scope: this,
            success: function(transport) {
                var value = this.slave.value;
                updateSelect(this.slave, transport.responseText);
                
                var option = this.slave.options[0];
                for (var i = 0, n = this.slave.options.length; i < n; i++) {
                    if (this.slave.options[i].value == value)
                        option = this.slave.options[i];
                }
                if (option) option.selected = true;
                
                if (this.options.afterUpdate)
                    this.options.afterUpdate();
            }
        });
    }
};

/**
 * Changes the innerHTML of a drop-down menu.
 * See http://code.google.com/p/ojay/source/browse/tags/0.1.2/source/core/dom_insertion.js
 * @param {HTMLElement} select
 * @param {String} html
 */
function updateSelect(select, html) {
    var div = document.createElement('div');
    div.innerHTML = '<select>' + html.replace(/\s*\n\s*/g, '') + '</select>';
    select.innerHTML = '';
    Array.from(div.firstChild.childNodes).forEach(function(node) {
        select.appendChild(node);
    });
};