StateMachine is a general purpose finite-state machine written in Kotlin.

Integration

At the project level build.gradle, add a maven repo pointing to https://jitpack.io, e.g.:

allprojects {
    repositories {
        google()
        maven { url "https://jitpack.io" } // this is it
        jcenter()
    }
}

At a module level build.gradle, add the following dependency:

implementation 'com.github.vitkhudenko:state_machine:0.3.9'

Usage

A sample configuration, assuming your app has Session class, that defines specific to your app events and states (Session.Event and Session.State enums):

val sessionStateMachine = StateMachine.Builder<Session.Event, Session.State>()
    .setInitialState(Session.State.ACTIVE)
    .addTransition(
        StateMachine.Transition(
            event = Session.Event.LOGIN,
            statePath = listOf(Session.State.INACTIVE, Session.State.ACTIVE)
        )
    )
    .addTransition(
        StateMachine.Transition(
            event = Session.Event.LOGOUT,
            statePath = listOf(Session.State.ACTIVE, Session.State.INACTIVE)
        )
    )
    .addTransition(
        StateMachine.Transition(
            event = Session.Event.LOGOUT_AND_FORGET,
            statePath = listOf(Session.State.ACTIVE, Session.State.FORGOTTEN)
        )
    )
    .build()

Meaning of the above sample configuration is that:

• There are 3 possible session states (ACTIVE, INACTIVE and FORGOTTEN).
• There are 3 possible events (LOGIN, LOGOUT and LOGOUT_AND_FORGET).
• StateMachine's initial state is ACTIVE.
• There are 3 possible state machine transitions:

Event	State path
LOGIN	INACTIVE -> ACTIVE
LOGOUT	ACTIVE -> INACTIVE
LOGOUT_AND_FORGET	ACTIVE -> FORGOTTEN

To move the sample sessionStateMachine to a new state your app should call consumeEvent() method:

// moves state machine from ACTIVE to INACTIVE state
sessionStateMachine.consumeEvent(Session.Event.LOGOUT)

State changes are propagated via StateMachine.Listener.

sessionStateMachine.addListener(object : StateMachine.Listener<Session.State> {
    override fun onStateChanged(oldState: Session.State, newState: Session.State) {
        // do something
    }
})

// or in a more concise way
sessionStateMachine.addListener { oldState, newState -> /* do something */ }

It is also possible to define transitions in a more concise way:

val sessionStateMachine = StateMachine.Builder<Session.Event, Session.State>()
    // ..
    .addTransitions(
        Session.Event.LOGIN to listOf(Session.State.INACTIVE, Session.State.ACTIVE),
        Session.Event.LOGOUT to listOf(Session.State.ACTIVE, Session.State.INACTIVE),
        Session.Event.LOGOUT_AND_FORGET to listOf(Session.State.ACTIVE, Session.State.FORGOTTEN)
    )

Test coverage

Test Coverage report

Threading

The StateMachine implementation is thread-safe. Public API methods are declared as synchronized.

The StateMachine is a synchronous tool, meaning it neither creates threads, nor uses thread pools or handlers.

License

MIT License

Copyright (c) 2019 Vitaliy Khudenko

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.