ampidentity.js

var centralLocation = "http://central.com/~tav/central.html",
    centralChannel,
    messageId = 0,
    messageQueue = [],
    callbackRegistry = {},
    firstContact = false;

function createCentralChannel() {
    if (centralChannel) {
        return;
    }
    centralChannel = document.createElement('iframe');
    document.body.appendChild(centralChannel);
    centralChannel.src = centralLocation;
}

function createChannel(dest) {
    var channel = document.createElement('iframe');
    document.body.appendChild(channel);
    channel.src = dest;
}

var identity = {
    getProvider: function(callback) {
        sendMessage({"do": "getProvider"}, callback);
    },
    setProvider: function(callback) {
        sendMessage({"do": "setProvider"}, callback);
    }
};

if (window.location.host === 'central.com') {

    var onMessage = function (event) {
        var msg = JSON.parse(event.data);
        var cmd = msg['do'];
        if (!cmd) {
            return;
        } else if (cmd === "setProvider") {
            var currentProvider = localStorage['provider'];
            if (!currentProvider) {
                alert("Setting provider to " + event.origin);
                localStorage['provider'] = event.origin;
            } else if (currentProvider !== event.origin) {
                alert('Boo!!');
            }
        } else if (cmd === "getProvider") {
            sendMessage(msg.id, localStorage['provider'], event.origin);
        }
    };

    var sendMessage = function (id, msg, scope) {
        if (window.parent) {
            msg = JSON.stringify({'id': id, 'data': msg});
            window.parent.postMessage(msg, scope);
        }
    };

    $(function () {
        sendMessage('y0!', "we're alive!", "*");
    });

    
} else {

    var sendMessage = function (msg, callback) {
        createCentralChannel();
        var id = msg['id'] = messageId++;
        msg = JSON.stringify(msg);
        if (callback) {
            callbackRegistry[id] = callback;
        }
        if (!firstContact) {
            messageQueue.push(msg);
        } else {
            centralChannel.contentWindow.postMessage(msg, centralLocation);
        }
    };

    var onMessage = function (event) {
        var msg = JSON.parse(event.data);
        var id = msg.id;
        var data = msg.data;
        // alert("incoming " + data);
        if (id === "confirm") {
        }
        firstContact = true;
        var callback = callbackRegistry[id];
        if (callback) {
            callback(data);
        }
        while (messageQueue.length) {
            centralChannel.contentWindow.postMessage(messageQueue.shift(), centralLocation);
        }
    };

}

if (typeof window.addEventListener !== 'undefined') { 
    window.addEventListener('message', onMessage, false); 
} else if (typeof window.attachEvent !== 'undefined') { 
    window.attachEvent('onmessage', onMessage); 
}