Inversion of control between Platform and App

[swirlds-automation]

This issue is outdated. The relation between Platform and App has already been refactored.

The main goal of this epic is to provide an API that makes it as easy + flexible as possible for an app developer to create an app that depend on the platform. In such case an app can have not only 1 platform but can 1-N platforms.

Current state

Today the platform is started by a main or by the browser and will start an application. This behavior is complex for app developers. Next to this there is a hard connection to the Browser that must be an optional component.

API idea

We discussed several ideas on the DevCon and the current idea looks like this:

It must be super easy for a developer to create an app and use the platform. The most easiest case should look like this:

class App {

    public static void main(String[] args) {
        final GlobalContext context = GlobalContextFactory.create();
        final Platform platform = PlatformFactory.create(context);
        platform.start();
    }
}

This code hides some details like the PlatformContext. A more complex example might look like this:

class App {

    public static void main(String[] args) {
        final GlobalContext globalContext = GlobalContextFactory.create("path/to/global.properties");
        final PlatformContext platformContext = PlatformContextFactory.create(globalContext, "path/to/app.properties");
        final Platform platform = PlatformFactory.create(platformContext);
        platform.start();
    }
}

Next to have this usecase (that uses the platform as a library) we still need to support the Browser and the functionallity to start & stop apps dynamically. Here is the example fake code from the DevCon:

class App implements Browsable {

    private Platform platform;

    @Override
    public void start(final GlobalContext globalContext ) {
        final PlatformContext platformContext = PlatformContextFactory.create(globalContext, "path/to/app.properties");
        platform = PlatformFactory.create(platformContext);
        platform.start();
    }

    @Override
    public void stop() {
        platform.stop();
    }

}

[swirlds-automation]

This epic is highly related to #5267 since the platform context and global context are needed _{author:hendrikebbers, createdAt:2022-09-15T20:49:43Z, updatedAt=2022-09-15T20:49:43Z}

[swirlds-automation]

We had an additional round of discussion (@netopyr @nathanklick @hendrikebbers ) and decided that the platform should be used like a library. That means that we do not will provide a workflow like it is sketched with the Browsable interface. An app developer will create a platform instance "by hand". We discussed that it will make sense to rename the Browser to "Developer Tools" and handle it like that. Everything that has a portal like usecase should be added in future and do not belong to the "Developer Tools". Maybe that would be not even a desktop app but an web app, who knows.. _{author:hendrikebbers, createdAt:2022-09-16T15:07:50Z, updatedAt=2022-09-16T15:07:50Z}

[swirlds-automation]

_{migrated from: url=https://github.com/swirlds/swirlds-platform/issues/6027 author:hendrikebbers, #:6027, createdAt:2022-09-15T19:59:30Z, updatedAt=2023-02-17T22:22:59Z labels=Epic,Migration:Base}