Charm browser story needs in-browser environment

[Gary Poster]

The charm browser story needs every gui instance to have their own in-memory environment. This should be a new implementation of app/store/env.js that is a drop-in replacement. It should respond correctly to commands, and also pump out the delta stream as needed to make the app work.

Initially, we only need to be able to choose at start-up time (in the app config.js) whether we have an in-memory environment or a "real" environment. In the future we will want to be able to dynamically switch these, and even instantiate multiple in-memory environments for other purposes. You shouldn't have to worry about this now, except to make the in-memory environment stand-alone and nicely tested.

After you tackle this, please make a separate bug/card to make this configuration available to the juju-gui charm. At least at the moment, that is a nice-to-have (low priority).

[Gary Poster (gary)]

Nice to have: the in-browser environment will use local persistent storage, specifically https://developer.mozilla.org/en-US/docs/IndexedDB . If you do this, make sure that the user does not get requested to store a DB until we actually need it. IWBNI you designed the system such that we can support multiple local environments in the future with a single user acceptance for all of them.