feat(fsm): rewrite with signal power

Special thanks to

Co-authored-by: David Khourshid <davidkpiano@gmail.com>

core/fsm/package.json

@@ -34,6 +34,7 @@
   "dependencies": {
     "@alwatr/logger": "^0.29.0",
     "@alwatr/type": "^0.29.0",
+    "@alwatr/signal": "^0.29.0",
     "tslib": "^2.5.0"
   }
 }

core/fsm/src/core.ts

@@ -1,74 +1,99 @@
 import {createLogger, globalAlwatr, type AlwatrLogger} from '@alwatr/logger';
+import {contextConsumer, type DispatchOptions} from '@alwatr/signal';
+import {dispatch} from '@alwatr/signal/core.js';
 
-import type {StringifyableRecord} from '@alwatr/type';
+import type {Stringifyable, StringifyableRecord} from '@alwatr/type';
 
 globalAlwatr.registeredList.push({
   name: '@alwatr/fsm',
   version: _ALWATR_VERSION_,
 });
 
-export interface StateConfig extends StringifyableRecord {
+export interface StateConfig<TEventId extends string, TState extends string> extends StringifyableRecord {
   /**
-   * An object mapping event name (keys) to state name
+   * An object mapping eventId (keys) to state.
    */
-  on?: Record<string, string | undefined>;
+  on?: Record<TEventId, TState | undefined>;
 }
 
-export interface MachineConfig extends StringifyableRecord {
+export interface MachineConfig<TState extends string, TEventId extends string, TContext extends Stringifyable>
+  extends StringifyableRecord {
   /**
-   * Machine ID.
+   * Machine ID (It is used in the state change signal identifier, so it must be unique).
    */
   id: string;
 
   /**
-   * Initial state name.
+   * Initial state.
    */
-  initial: string;
+  initial: TState;
+
+  /**
+   * Initial context.
+   */
+  context: TContext;
 
   /**
    * States list
    */
-  states: Record<string, StateConfig | undefined>;
+  states: Record<TState | '_', StateConfig<TEventId, TState> | undefined>;
 }
 
-export class FiniteStateMachine {
-  currentState;
+export class FiniteStateMachine<
+  TState extends string = string,
+  TEventId extends string = string,
+  TContext extends Stringifyable = StringifyableRecord
+> {
+  stateConsumer;
+  context: TContext;
+
   protected _logger: AlwatrLogger;
 
-  constructor(public config: MachineConfig) {
+  get gotState(): TState {
+    return this.stateConsumer.getValue() ?? this.config.initial;
+  }
+
+  protected setState(value: TState, options?: DispatchOptions): void {
+    dispatch(this.stateConsumer.id, value, options);
+  }
+
+  constructor(public readonly config: Readonly<MachineConfig<TState, TEventId, TContext>>) {
     this._logger = createLogger(`alwatr/fsm:${config.id}`);
     this._logger.logMethodArgs('constructor', config);
-    this.currentState = config.initial;
-    if (this.currentState in config.states === false) {
+    this.context = config.context;
+    this.stateConsumer = contextConsumer.bind<TState>('finite-state-machine-' + this.config.id);
+    this.setState(config.initial);
+    if (!config.states[config.initial]) {
       this._logger.error('constructor', 'invalid_initial_state', config);
     }
   }
 
   /**
-   *
-   * @param eventName
+   * Machine transition.
    */
-  transition(eventName: string): string {
-    const nextState = this.config.states[this.currentState]?.on?.[eventName] ??
-      this.config.states._?.on?.[eventName];
+  transition(toEventId: TEventId, newContext?: TContext, options?: DispatchOptions): TState | null {
+    const state = this.gotState;
+    const nextState = this.config.states[state]?.on?.[toEventId] ?? this.config.states._?.on?.[toEventId];
 
-    this._logger.logMethodFull('transition', eventName, nextState);
+    this._logger.logMethodFull('transition', {toEventId, newContext}, nextState);
 
-    if (nextState) {
-      this.currentState = nextState;
+    if (newContext !== undefined) {
+      this.context = newContext;
     }
-    else {
+
+    if (nextState == null) {
       this._logger.incident(
           'transition',
           'invalid_target_state',
           'Defined target state for this event not found in state config',
           {
-            eventName,
-            [this.currentState]: {...this.config.states._?.on, ...this.config.states[this.currentState]?.on},
+            eventName: toEventId,
+            [state]: {...this.config.states._?.on, ...this.config.states[state]?.on},
           },
       );
+      return null;
     }
 
-    return this.currentState;
-  }
+    this.setState(nextState, options);
+    return nextState;
 }

core/fsm/tsconfig.json

@@ -12,5 +12,6 @@
   "references": [
     {"path": "../logger"},
     {"path": "../type"},
+    {"path": "../signal"},
   ]
 }