// *** Service Calling Proxy Class
// Thanks to Rick for this:
//http://www.west-wind.com/weblog/posts/324917.aspx

function serviceProxy(serviceUrl)

{
    var _I = this;
    this.serviceUrl = serviceUrl;
    // *** Call a wrapped object
    this.invoke = function(method, data, callback, error, bare) {
    
        // *** Convert input data into JSON - REQUIRES Json2.js
        var json = JSON2.stringify(data); 
        // *** The service endpoint URL   
        var url = _I.serviceUrl + method;

        $.ajax( { 
                    url: url,
                    data: json,
                    type: "POST",
                    processData: false,
                    contentType: "application/json",
                    timeout: 10000,
                    dataType: "text",  // not "json" we'll parse
                    success: 
                    function(res) 
                    {                                   

                        if (!callback) return;
 
                        // *** Use json library so we can fix up MS AJAX dates
                        var result = JSON2.parse(res);
                        // *** Bare message IS result
                        if (bare)
                        { callback(result); return; }
                        // *** Wrapped message contains top level object node
                        // *** strip it off
                        for(var property in result)
                        {
                            callback( result[property] );
                            break;
                        }                   

                    },

                    error:  function(xhr) {

                        if (!error) return;

                        if (xhr.responseText)

                        {

                            var err = JSON2.parse(xhr.responseText);

                            if (err)

                                error(err); 

                            else    

                                error( { Message: "Unknown server error." })

                        }

                        return;

                    }

                });   

    }

}