/*
 * ***** BEGIN LICENSE BLOCK *****
 * Copyright (c) 2011-2012 VMware, Inc.
 *
 * For the license see COPYING.
 * ***** END LICENSE BLOCK *****
 */

// The simplest and most robust transport, using the well-know cross
// domain hack - JSONP. This transport is quite inefficient - one
// mssage could use up to one http request. But at least it works almost
// everywhere.
// Known limitations:
//   o you will get a spinning cursor
//   o for Konqueror a dumb timer is needed to detect errors


var JsonPTransport = SockJS['jsonp-polling'] = function(ri, trans_url) {
    utils.polluteGlobalNamespace();
    var that = this;
    that.ri = ri;
    that.trans_url = trans_url;
    that.send_constructor(jsonPGenericSender);
    that._schedule_recv();
};

// Inheritnace
JsonPTransport.prototype = new BufferedSender();

JsonPTransport.prototype._schedule_recv = function() {
    var that = this;
    var callback = function(data) {
        that._recv_stop = null;
        if (data) {
            // no data - heartbeat;
            if (!that._is_closing) {
                that.ri._didMessage(data);
            }
        }
        // The message can be a close message, and change is_closing state.
        if (!that._is_closing) {
            that._schedule_recv();
        }
    };
    that._recv_stop = jsonPReceiverWrapper(that.trans_url + '/jsonp',
                                           jsonPGenericReceiver, callback);
};

JsonPTransport.enabled = function() {
    return true;
};

JsonPTransport.need_body = true;


JsonPTransport.prototype.doCleanup = function() {
    var that = this;
    that._is_closing = true;
    if (that._recv_stop) {
        that._recv_stop();
    }
    that.ri = that._recv_stop = null;
    that.send_destructor();
};


// Abstract away code that handles global namespace pollution.
var jsonPReceiverWrapper = function(url, constructReceiver, user_callback) {
    var id = 'a' + utils.random_string(6);
    var url_id = url + '?c=' + escape(WPrefix + '.' + id);

    // Unfortunately it is not possible to abort loading of the
    // script. We need to keep track of frake close frames.
    var aborting = 0;

    // Callback will be called exactly once.
    var callback = function(frame) {
        switch(aborting) {
        case 0:
            // Normal behaviour - delete hook _and_ emit message.
            delete _window[WPrefix][id];
            user_callback(frame);
            break;
        case 1:
            // Fake close frame - emit but don't delete hook.
            user_callback(frame);
            aborting = 2;
            break;
        case 2:
            // Got frame after connection was closed, delete hook, don't emit.
            delete _window[WPrefix][id];
            break;
        }
    };

    var close_script = constructReceiver(url_id, callback);
    _window[WPrefix][id] = close_script;
    var stop = function() {
        if (_window[WPrefix][id]) {
            aborting = 1;
            _window[WPrefix][id](utils.closeFrame(1000, "JSONP user aborted read"));
        }
    };
    return stop;
};
