eewing
79 lines
2.6 KiB
JavaScript
79 lines
2.6 KiB
JavaScript
export function isLifecycleFnMeta(meta) {
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return (!!meta &&
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typeof meta === "object" &&
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"to" in meta &&
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"from" in meta &&
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"event" in meta &&
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"args" in meta);
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}
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/**
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* Defines a strongly-typed finite state machine.
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*
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* @see {@link https://runed.dev/docs/utilities/finite-state-machine}
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*/
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export class FiniteStateMachine {
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#current = $state();
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states;
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#timeout = {};
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constructor(initial, states) {
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this.#current = initial;
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this.states = states;
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this.send = this.send.bind(this);
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this.debounce = this.debounce.bind(this);
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// synthetically trigger _enter for the initial state.
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this.#dispatch("_enter", { from: null, to: initial, event: null, args: [] });
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}
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#transition(newState, event, args) {
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const metadata = { from: this.#current, to: newState, event, args };
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this.#dispatch("_exit", metadata);
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this.#current = newState;
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this.#dispatch("_enter", metadata);
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}
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#dispatch(event, ...args) {
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const action = this.states[this.#current]?.[event] ?? this.states["*"]?.[event];
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if (action instanceof Function) {
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if (event === "_enter" || event === "_exit") {
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if (isLifecycleFnMeta(args[0])) {
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action(args[0]);
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}
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else {
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console.warn("Invalid metadata passed to lifecycle function of the FSM.");
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}
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}
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else {
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return action(...args);
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}
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}
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else if (typeof action === "string") {
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return action;
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}
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else if (event !== "_enter" && event !== "_exit") {
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console.warn("No action defined for event", event, "in state", this.#current);
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}
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}
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/** Triggers a new event and returns the new state. */
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send(event, ...args) {
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const newState = this.#dispatch(event, ...args);
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if (newState && newState !== this.#current) {
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this.#transition(newState, event, args);
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}
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return this.#current;
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}
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/** Debounces the triggering of an event. */
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async debounce(wait = 500, event, ...args) {
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if (this.#timeout[event]) {
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clearTimeout(this.#timeout[event]);
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}
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return new Promise((resolve) => {
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this.#timeout[event] = setTimeout(() => {
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delete this.#timeout[event];
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resolve(this.send(event, ...args));
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}, wait);
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});
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}
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/** The current state. */
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get current() {
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return this.#current;
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}
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}
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