View source for Pancake/French Toast/Message API

=== User stories ===

==== As a front-end developer, I need a way to tell the native app to open a new layer containing a specific layer state. ====

  FrenchToast.openApplicationView(url)

==== As a front-end developer, I need a way to tell the native app to open a URL in the viewer. ====

  FrenchToast.openPublicView(url)

''I don't think we need the name parameter. I don't think we want layers to be able to talk directly to each other. Instead, I believe we can stick to a service-oriented architecture based on URLs.'' -[[Gbrander]]

==== As a front-end developer, I need the app to tell me when a layer has received focus so that I can check for updates and refresh data if necessary. ====

What about a DOM event?

  window.addEventListener('layerFocus', fn)

'' Focus isn't quite the same as active/visible. On the desktop, focus doesn't happen until an element in the window receives focus. I'm not sure how that plays out on touch devices. I think we want visibility''

''There is an actual API for this: [http://dvcs.w3.org/hg/webperf/raw-file/tip/specs/PageVisibility/Overview.html PageVisibility] but we would have to investigate browser support. As I understand it, our "layers" are going to be window object in UiWebViews or their equivalent, so this seems like the right place to start. I would rather polyfill this though than invent our own.'' 

* http://davidwalsh.name/page-visibility
* https://developer.mozilla.org/en-US/docs/DOM/Using_the_Page_Visibility_API
* https://github.com/ai/visibility.js

==== As a front-end developer, I need a way to securely ''verify that the user is authenticated'' so that I do not expose confidential information. ====

  // find out if the current session is valid
  FrenchToast.getSession()
  
  // to start browserid
  FrenchToast.startBrowserId(callback)
  
  // to validate the browserid token
  FrenchToast.validateBrowserIdReceipt(receipt, callback)

''Can somebody who worked on the session stuff in the past verify that these could satisfy the user story?'' - [[Gbrander]]

''What about the way it works today are we wanting to fix? This functionality currently resides in the misnamed/misplaced [https://github.com/mozillapancake/pancake-ft-client/blob/app-skeleton/js/lib/signin.js lib/signin]. ISTM that the modules under service/* could be FrenchToast.*. Lets talk.'' - [[Sfoster]]

==== As a front-end developer, I need access to a shared store that persists across sessions. All layers should have access to this store. ====

Use standard localStorage to serialize/deserialize persisted app data.

  window.localStorage
  JSON.stringify
  JSON.parse

''Can we confirm that the same localStorage is available between UIWebViews'' - [[Gbrander]]

=== Discussion ===

''I don't think we need a general message mechanism to talk to the app. I also don't think we need to be able to send messages to specific layers from specific layers. In general, I would like to make the coupling between layers loose, and based on requesting URLs be opened. The layer itself can decide what to do with the URL.'' -[[Gbrander]]

''Agreed that urls should be the primary messaging mechanism. We also have storage events which (browser-support willing) should allow us to signal state changes like login/logout across windows/layers. I suspect there's still a need for the native/js messaging though.