g

import Toybox.Lang;

(:background) function isBackground() as Boolean {
    // return evcc.isBackground;
    return true; // for testing purposes
}

class A_FG extends A_BG {
    function initialize() {
        A_BG.initialize();
    }

    function notNeededInBackground() as Void {
        // [NOTE 1]
        // this assumes that B_BG has an empty implementation
        // of notNeededInBackground(), for convenience
        _b.notNeededInBackground();
        // if not, use the following code instead:
        // (_b as B_FG).notNeededInBackground();
    }
}

(:background) class A_BG {
    protected var _b as B_BG;

    function initialize() {
        // some complicated logic
        _b = B_BG.create();
        // some complicated logic
    }

    function neededInBackground() as Void {
        _b.neededInBackground();
    }
}

//! Do not directly call `new B_FG()`; use B_BG.create() instead
class B_FG extends B_BG {
    // would've been nice if this could've been protected
    function initialize(_doNotCallDirectly as Number, _seriouslyDontDoIt as Symbol) {
        B_BG.initialize(42, :initialize);
    }

    function notNeededInBackground() as Void {
        // do stuff
        // ...
    }
}


//! Do not directly call `new B_BG()`; use B_BG.create() instead
(:background) class B_BG {
    // would've been nice if this could've been protected
    function initialize(_doNotCallDirectly as Number, _seriouslyDontDoIt as Symbol) {
        // ...
    }

    (:typecheck(disableBackgroundCheck))
    static public function create() as B_BG {
        if (isBackground()) {
            return new B_BG(42, :initialize);
        } else {
            return new B_FG(42, :initialize);
        }
    }

    function neededInBackground() as Void {
        // do stuff
        // ...
    }

    // empty stub function
    // See [NOTE 1] above
    function notNeededInBackground() as Void {
        // do nothing
    }
}