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State machine in Kotlin
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| class StateMachine(private val initialState: State) { | |
| interface Event | |
| interface State | |
| class Edge(private val triggerEvent: Event, private val targetState: State) { | |
| private val actionList = mutableListOf<(Edge) -> Unit>() | |
| fun action(action: (Edge) -> Unit) { | |
| actionList.add(action) | |
| } | |
| //Invoke when you go down the edge to another state | |
| fun enterEdge(): State { | |
| actionList.forEach { it(this) } | |
| return targetState | |
| } | |
| fun canHandleEvent(event: Event): Boolean = (event == triggerEvent) | |
| } | |
| class StateWrapper(val state: State) { | |
| private val edgeList = mutableListOf<Edge>() | |
| fun edge(event: Event, targetState: State, init: Edge.() -> Unit = {}) { | |
| edgeList.add(Edge(event, targetState).apply { init() }) | |
| } | |
| private val stateEnterAction = mutableListOf<(State) -> Unit>() | |
| //Add an action which will be called when the state is entered | |
| fun action(action: (State) -> Unit) { | |
| stateEnterAction.add(action) | |
| } | |
| fun enterState() { | |
| stateEnterAction.forEach { it(this.state) } | |
| } | |
| //Get the appropriate Edge for the Event | |
| fun getEdgeForEvent(event: Event): Edge? = edgeList.firstOrNull { it.canHandleEvent(event) } | |
| } | |
| companion object { | |
| fun buildStateMachine(initialState: State, init: StateMachine.() -> Unit): StateMachine = | |
| StateMachine(initialState).apply(init) | |
| } | |
| private lateinit var currentState: StateWrapper | |
| private val stateList = mutableListOf<StateWrapper>() | |
| fun state(state: State, init: StateWrapper.() -> Unit) { | |
| if (stateList.firstOrNull { it.state == state } != null) { | |
| throw IllegalStateException("Duplicate state found") | |
| } | |
| val stateWrapper = StateWrapper(state).apply(init) | |
| stateList += stateWrapper | |
| if (state == initialState) { | |
| currentState = stateWrapper | |
| } | |
| } | |
| fun eventOccurred(event: Event) { | |
| val edge = currentState.getEdgeForEvent(event) ?: return | |
| val newState = edge.enterEdge() | |
| val stateWrapper = stateList.first { newState == it.state } | |
| stateWrapper.enterState() | |
| currentState = stateWrapper | |
| } | |
| } | |
| // Example | |
| fun example() { | |
| val stateMachine = StateMachine.buildStateMachine(initialState) { | |
| state(PlayerState.Uninitialized) { | |
| edge(PlayerEvent.InitializePlaying, PlayerState.ReadyToPlay) | |
| edge(PlayerEvent.InitializeRecording, PlayerState.ReadyToRecord) | |
| } | |
| state(PlayerState.ReadyToRecord) { | |
| action { | |
| view.prepareToRecord() | |
| view.updateTimer(0) | |
| } | |
| edge(PlayerEvent.StartRecording, PlayerState.Recording) { | |
| action { } | |
| } | |
| edge(PlayerEvent.StopRecording, PlayerState.ReadyToRecord) | |
| } | |
| state(PlayerState.ReadyToPlay) { | |
| action { } | |
| edge(PlayerEvent.Trash, PlayerState.ReadyToRecord) { | |
| action { } | |
| } | |
| edge(PlayerEvent.StartPlaying, PlayerState.Playing) { | |
| action { } | |
| } | |
| edge(PlayerEvent.Save, PlayerState.Saved) { | |
| action { } | |
| } | |
| } | |
| } | |
| } |
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