/*
url-loading object and a request queue built on top of it
*/

/* namespacing object */
var net = new Object();

net.READY_STATE_UNINITIALIZED = 0;
net.READY_STATE_LOADING = 1;
net.READY_STATE_LOADED = 2;
net.READY_STATE_INTERACTIVE = 3;
net.READY_STATE_COMPLETE = 4;


/*--- content loader object for cross-browser requests ---*/
net.ContentLoader = function() {
    this.req = null;

    if (window.XMLHttpRequest) {
        this.req = new XMLHttpRequest();
    } else if (window.ActiveXObject) {
        this.req = new ActiveXObject("Microsoft.XMLHTTP");
    }
}

net.ContentLoader.prototype = {
    sendRequest:function(url, onload, onerror, method, params, contentType, username, password, headers) {
        this.onload = onload;
        this.onerror = (onerror) ? onerror : this.defaultError;
        if (!method) {
            method = "GET";
        }

        if (!contentType && method == "POST") {
            contentType = 'application/x-www-form-urlencoded';
        }
        if (this.req) {
            try {
                var loader = this;
                this.req.onreadystatechange = function() {
                    loader.onReadyState.call(loader);
                }
                this.req.open(method, url, true);
                if (contentType) {
                    this.req.setRequestHeader('Content-Type', contentType);
                }
                if (headers) {
                    var keys = headers.keys();
                    for (var i = 0; i < keys.length; i++) {
                        var key = keys[i];
                        this.req.setRequestHeader(key, headers.get(key));
                    }
                }

                this.req.send(params);
            } catch (err) {                
                this.onerror.call(this);
            }
        } else {
            alert('XMLHTTPRequest object not instantiated');
        }
    },

    onReadyState:function() {
        var ready = this.req.readyState;
        if (ready == net.READY_STATE_COMPLETE) {
            var httpStatus = this.req.status;
            if (httpStatus == 200 || httpStatus == 0) {
                this.onload.call(this);
            } else {
                this.onerror.call(this);
            }
        }
    },

    defaultError:function() {
        alert("error fetching data!"
                + "\n\nreadyState:" + this.req.readyState
                + "\nstatus: " + this.req.status
                + "\nheaders: " + this.req.getAllResponseHeaders());
    }
}



/*--- queue system for efficient transfer of many small commands in a single request ---*/
net.cmdQueues = new Array();


net.CommandQueue = function(id, url, onUpdate, freq) {
    this.id = id;
    net.cmdQueues[id] = this;
    this.url = url;
    this.queued = new Array();
    this.sent = new Array();
    this.onUpdate = onUpdate;
    if (freq) {
        this.repeat(freq);
    }
    this.lastUpdateTime = 0;
}

net.CommandQueue.STATUS_QUEUED = -1;
net.CommandQueue.STATE_UNINITIALIZED = net.READY_STATE_UNINITIALIZED;
net.CommandQueue.STATE_LOADING = net.READY_STATE_LOADING;
net.CommandQueue.STATE_LOADED = net.READY_STATE_LOADED;
net.CommandQueue.STATE_INTERACTIVE = net.READY_STATE_INTERACTIVE;
net.CommandQueue.STATE_COMPLETE = net.READY_STATE_COMPLETE;
net.CommandQueue.STATE_PROCESSED = 5;

net.CommandQueue.PRIORITY_NORMAL = 0;
net.CommandQueue.PRIORITY_IMMEDIATE = 1;


net.CommandQueue.prototype = {
    addCommand:function(command) {
        if (this.isCommand(command)) {
            this.queue.append(command, true);
            if (command.priority == net.CommandQueue.PRIORITY_IMMEDIATE) {
                this.fireRequest();
            }
        }
    },

    fireRequest:function() {
        if (!this.onUpdate && this.queued.length == 0) {
            return;
        }
        var data = "lastUpdate=" + this.lastUpdateTime + "&data=";
        for (var i = 0; i < this.queued.length; i++) {
            var cmd = this.queued[i];
            if (this.isCommand(cmd)) {
                data += cmd.toRequestString();
                this.sent[cmd.id] = cmd;
            }
        }
        this.queued = new Array();
        this.loader = new net.ContentLoader(
                this.url,
                net.CommandQueue.onload,
                net.CommandQueue.onerror,
                "POST", data
                );
    },

    isCommand:function(obj) {
        return (
                obj.implementsProp("id")
                        && obj.implementsProp("priority")
                        && obj.implementsFunc("toRequestString")
                        && obj.implementsFunc("parseResponse")
                );
    },

    repeat:function(freq) {
        this.unrepeat();
        if (freq > 0) {
            this.freq = freq;
            var cmd = "net.cmdQueues[" + this.id + "].fireRequest()";
            this.repeater = setInterval(cmd, freq * 1000);
        }
    },

    unrepeat:function() {
        if (this.repeater) {
            clearInterval(this.repeater);
        }
        this.repeater = null;
    }
}

net.CommandQueue.onload = function() {
    var xmlDoc = this.req.responseXML;
    var elDocRoot = xmlDoc.getElementsByTagName("responses")[0];
    var lastUpdate = elDocRoot.attributes.getNamedItem("updateTime");
    if (parseInt(lastUpdate) > this.lastUpdateTime) {
        this.lastUpdateTime = lastUpdate;
    }
    if (elDocRoot) {
        for (i = 0; i < elDocRoot.childNodes.length; i++) {
            elChild = elDocRoot.childNodes[i];
            if (elChild.nodeName == "command") {
                var attrs = elChild.attributes;
                var id = attrs.getNamedItem("id").value;
                var command = net.commandQueue.sent[id];
                if (command) {
                    command.parseResponse(elChild);
                }
            } else if (elChild.nodeName == "update") {
                if (this.implementsFunc("onUpdate")) {
                    this.onUpdate.call(this, elChild);
                }
            }
        }
    }
}

net.CommandQueue.onerror = function() {
    alert("problem sending the data to the server");
}