feat: Add fsm operator

README.md

@@ -86,13 +86,11 @@ Another approach is to avoid the _machine_ object and use this library in a pipe
 
 ```ts
 const {
-  nextState,
+  fsm,
   markInput,
 } = fsmHelpersFactory<State, Input>(transitions);
 
-const state$ = input$.pipe(
-  scan(nextState, initialState),
-);
+const state$ = input$.pipe(fsm(initialState));
 
 state$.subscribe(console.log);
 ```

examples/example-1.ts

@@ -2,21 +2,22 @@ import { Subject, merge, scan } from 'rxjs';
 
 import { fsmHelpersFactory } from '../lib';
 
-import { Input, State, transitions } from './state.config';
+import { Input, State, initialState, transitions } from './state.config';
 
 /**
  * Example 1
  * Demonstrates creating a FSM only by using RxJs operators.
  */
 
-const { nextState, markInput } = fsmHelpersFactory<State, Input>(transitions);
+const {
+  nextState,
+  markInput,
+} = fsmHelpersFactory<State, Input>(transitions);
 
 // Define inputs
 const toggle$ = new Subject<void>();
 const hide$ = new Subject<void>();
 
-const initialState: State = 'hidden';
-
 // Use helper functions
 const input$ = merge(
   toggle$.pipe(markInput('toggle')),

examples/example-2.ts

@@ -1,7 +1,7 @@
-import { Observable, Subject, merge } from 'rxjs';
+import { Subject, merge } from 'rxjs';
 
 import { fsmHelpersFactory, rxjsFsmFactory } from '../lib';
-import { Input, State, transitions } from './state.config';
+import { Input, State, initialState, transitions } from './state.config';
 
 /**
  * Example 2
@@ -12,8 +12,6 @@ import { Input, State, transitions } from './state.config';
 const toggle$ = new Subject<void>();
 const hide$ = new Subject<void>();
 
-const initialState: State = 'hidden';
-
 const { markInput } = fsmHelpersFactory<State, Input>(transitions);
 
 // Use helper functions

examples/example-3.ts

@@ -0,0 +1,41 @@
+import { Subject, merge } from 'rxjs';
+
+import { fsmHelpersFactory } from '../lib';
+
+import { Input, State, initialState, transitions } from './state.config';
+
+/**
+ * Example 3
+ * Demonstrates creating a FSM using by the `fsm` operator.
+ */
+
+const {
+  markInput,
+  fsm,
+} = fsmHelpersFactory<State, Input>(transitions);
+
+// Define inputs
+const toggle$ = new Subject<void>();
+const hide$ = new Subject<void>();
+
+// Use helper functions
+const input$ = merge(
+  toggle$.pipe(markInput('toggle')),
+  hide$.pipe(markInput('hide')),
+);
+
+const state$ = input$.pipe(fsm(initialState));
+
+// Listen
+state$.subscribe((newState) => console.log('New state:', newState));
+
+console.log('Initial state:', initialState);
+console.log('Input: toggle');
+toggle$.next();
+console.log('Input: toggle');
+toggle$.next();
+console.log('Input: toggle');
+toggle$.next();
+
+console.log('Input: hide');
+hide$.next();

examples/state.config.ts

@@ -3,6 +3,8 @@ import { StateTransitions } from '../lib';
 export type Input = 'toggle' | 'hide';
 export type State = 'hidden' | 'shown';
 
+export const initialState: State = 'hidden';
+
 export const transitions: StateTransitions<State, Input> = {
   hidden: {
     toggle: 'shown',

lib/rxjs-fsm/helpers.ts

@@ -1,9 +1,13 @@
-import { markInput, nextState } from '../utils';
+import { fsm, markInput, nextState } from '../utils';
 import { BaseInput, BaseState, StateTransitions } from '../models';
 
 /**
  * Factory for helper functions, independent of state machine instance.
  */
 export const fsmHelpersFactory = <S extends BaseState, T extends BaseInput>(
   transitions: StateTransitions<S, T>,
-) => ({ markInput: markInput<unknown, T>(), nextState: nextState<S, T>(transitions) });
+) => ({
+  markInput: markInput<unknown, T>(),
+  nextState: nextState<S, T>(transitions),
+  fsm: fsm(transitions),
+});

lib/utils/fsm.ts

@@ -0,0 +1,12 @@
+import { pipe, scan, startWith } from 'rxjs';
+import { BaseInput, BaseState, StateTransitions } from '../models';
+import { nextState } from './next';
+
+export const fsm = <S extends BaseState, T extends BaseInput>(
+  transitions: StateTransitions<S, T>,
+) => (
+  initialState: S,
+) => pipe(
+  scan(nextState<S, T>(transitions), initialState),
+  startWith(initialState),
+);

lib/utils/index.ts

@@ -1,2 +1,3 @@
 export * from './mark-input';
 export * from './next';
+export * from './fsm';