Use an ECS for event management

[conradludgate]

I've been a bit busy recently, there's an idea I wanted to work on but so far haven't had the time. Thought I'd put it here instead.

Currently this crate is based on explicit event handlers and emits. It's also seemingly mirroring some inheritance based design.

What came to mind is that hermes-five is somewhat like a game engine. The devices are like NPC characters in a game world, which respond to events in order to move around. One of the leading database engines in Rust at the moment is Bevy. Cut out all the audio and visual and you are left with https://docs.rs/bevy_ecs/latest/bevy_ecs/.

I haven't actually attempted refactoring hermes-five to use bevy yet, but it's an interesting idea to me. When I have time I will attempt it just to see. I don't know if the API will really be that great, but I want to see nonetheless.

There's also some scripting support in some third party crates that would be interesting to explore
https://github.com/jarkonik/bevy_scriptum
https://github.com/makspll/bevy_mod_scripting

[dclause]

For clarity, i will refer to a dev using Hermes-Five as User and to someone using the UI of Hermes-Studio as EndUser .

Quick take:
It is true that a robot can be seen as a PNJ (or a game where devices are the PNJs). In this context, using Bevy gains the maturity of entity-component and plugin-system and all other things in Bevy. However, I have compatibility concerns with the current project scope and technical feasibilty due to some pecific requirements. Beyond feasibility, I wonder if Bevy could be completely hidden behind Hermes-Five so that the User does not have to learn Rust, Hermes-Five and Bevy (a huge stack all-together) to start his hobbyist simple project.

Concerns
In no particular order, but hopefully still comprehensible:

• Async, Scheduler versus API Rest/websocket (axum) compatibility
  Currently, Hermes-Studio exists in the form of a decoupled vueJS project over Hermes-Five, with the backend be a REST+Websocket API using Axum, a database, and some custom logic. How would that work along with Bevy ?
  More specifically: Can Bevy’s world.run() coexist non-blocking, along with a webserver ?

• The purpose of Hermes-Five is for developer Users to focus on there robot. The API is done to maximize you thinking in term of hardware (board, devices, etc..) and how they connect together. Can Bevy be hidden behind Hermes-Five in a nice way so that the API (and the examples in the project) look similar to now.
  More specifically: Can we stay an Hermes project using Bevy underneath, or does developers robot becomes a Bevy project ? How would look like the current User facing API ? Would it be pure Lua script to be written (injected underneath into Hermes-Bevy system) ?

• Memory / CPU footprint:
  Hermes Five / Studio purpose is to run inside the robot. Therefore I would like to check how having both bevy event-loop + the axum event-loop could overload the processor leading to excessive current consumption in a robot or too much usage on low-capability CPUs like RaspberryZero

• Async callbacks and event:
  I do suppose that in a video games multiples NPCs can respond in parallel to a same user input event (run the sound, change the music, reaction of NPCs, etc...) so I suppose all my event related code can be turned into Bevy's event system. However, from what I see in the examples that is strongly typed, so I might have the same limitation as per our current try at typing events, and thus also have problems with the various device "onChange" events.

• Role of Hermes-Five vs Hermes-Studio vs Bevy
  From what I understand from your post, Bevy kind of makes Hermes-Five actually useless. Because the whole point would be to move toward Hermes-Studio, which means Hermes-Five is no longer needed underneath. Hermes-Studio would work over Bevy, not Hermes-Five. Bevy would provide the input, the output, the plugin system, the scripting, probably even the UI ? And Hermes-Five becomes useless a that point. For the EndUser its fine, but that means we don't have a simple developer API for the hobbyist User.

• Bevy vs extensible UI
  What UI is Bevy using ? egui, doxide, or custom something ? Can it generate a browser based UI ? Can I build anything in SVG, html/Css or other inside that ? For instance my Hermes-Studio timeline https://raw.githubusercontent.com/dclause/hermes-studio/refs/heads/develop/docs/public/samples/timeline_connected.png
  If not, than it means it has to be couple with yet another GUI engine or expose an API for decoupled UI.

• Bevy vs input system
  In Hermes-Five, every input/ouput goes though the Transport Layer. This means, devices do constant polling on the transport layer
  (see https://github.com/dclause/hermes-five/blob/develop/hermes-five/src/devices/input/digital.rs) to check the new value of the hardware pin, and trigger onChange event to the User facing API. Is this compatible with Bevy input system ?
  More specifically: Can we implement input device polling in the form of Bevy input device, like a "Gamepad, Mouse or TouchScreen" is.

Experiments needed:

• Bevy+Axum server
• Bevy + serial polling input
• Benchmark CPU/memory usage
• Does it deprecates Hermes-Five as the fondation of Hermes-Studio ?
• Bevy + webUI

The minimal feasability test would consists of having the embedded led of an Arduino board to blink when connected to a computer.