State Machine Redux

Purpose

This project is a simplified state machine with add-ons for complexity as needed. It is designed to be usable for everything from games to business logic cases. It is a light-weight framework that can be extended.

Installation

All libraries are available on maven central.

Library	Purpose	Version
smr	Core Library
smr-metrics	Metrics addon
smr-yml	YAML support

Build out

The goal is to put together a state machine that is self-contained. Once it has the features needed for it, then provide a way for the state machine to work with multiple contexts; each context has its own existing state and a context can transition between states with the callbacks being notified. Though that complexity is not needed. You can simply use the state machine as a single state self-determined. This is perfect for situations where there is only one in the system, such as managing the state of an application starting, or a player in a game.

But when you want to apply a state machine broadly to many objects, each with their own state but they function the same, that's where we want to model one state machine with many concurrent contexts.

The mistake with the original implementation was that this complex pattern was built first, making it impossible to understand the simple use-case.

TODO

1. Ability to create the state machine definition from a file.
2. Hooks at each stage.
   1. Metrics extension
3. Publish library to maven
4. Consider a State Machine Engine to handle multiple contexts for the same state machine.

Example

Simple example where we focus on a single state machine and the context is defined in the code.

  // Setup State machine
   StateMachine sm = StateMachine.builder()
       .addState(IDLE).addState(RUN).addState(JUMP)
       .setInitialState(IDLE)
       .addTransition(IDLE, SPACEBAR, JUMP)
       .addTransition(RUN, SPACEBAR, JUMP)
       .addTransition(JUMP, END_ACTION, IDLE)
       .addTransition(RUN, END_ACTION, IDLE)
       .addTransition(IDLE, ACTION_BUTTON, RUN)
       .build();

    sm.enable(IDLE, Event.TICK, (c)->idleModeDisplay());
    sm.enable(RUN, Event.TICK, (c)->runModeDisplay());
    sm.enable(RUN, Event.TICK, (c)->runModeDisplay());
    sm.enable(JUMP, Event.ENTER, (c)->startAnimation("jump"));
    sm.enable(RUN, Event.ENTER, (c)->startAnimation("run"));

An example where the context for the state that is changing is external to the state machine: