I have a non-trivial component which requires a bunch of internal and
external collaborators to work. This component is itself re-usable.
What I really want to do is have ReusableComponent be a component in a
system so it can pull its external collaborators. However,
ReusableComponent constructs its own services etc. so it really want to be
(or at least have access to) a system.
For example, let's say I have the following:
(defrecord InternalToReusableComponent [bus]
(component/Lifecycle
(start [this]...))
(defrecord ReusableComponent [bus logger]
(component/Lifecycle
(start [this]
this)
....))
(defn reusable-component-system [external-collaborator]
(component/system-map
:bus (....)
:logger (....)
:reusable-component (component/using (map->ReusableComponent {}) [:bus
:logger external-collaborator]))
Fine - I now have a system from which I can pull the reusable component.
However, where does 'external-collaborator' come from? Obviously there is a
larger system which I want this component to be part of so I can do:
(defn larger-system []
(component/system-map
:external-collaborator (...)
:reusable-component (component/using (some-magic-glue)
[:external-collaborator])))
I am struggling to see what (some-magic-glue) should be. I imagine it needs
to be something like:
(defrecord SystemAdaptor [external-collaborator internal-system]
component/Lifecycle
(start [this]
(let [internal-system (or internal-system (reusable-component-system
external-collaborator))
internal-system (component/start internal-system)]
(assoc this :internal-system internal-system)))
(stop [this]
(let [internal-system (:internal-system this)
internal-system (component/stop internal-system]
(assoc this :internal-system internal-system)))
but it all feels a bit yuck.
I can't merge the two systems because the reusable component is chocka full
of very fine grained command handlers and both the internal and external
systems will have their own 'bus' for example. I could namespace the keys
but that again feels painful...
Hope that is clear - and I look forward to your thoughts :).
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