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BehaviorSubject,
map,
Observable,
of,
sample,
Subject,
Subscription,
switchMap,
takeUntil,
zip,
} from 'rxjs';
import { Rule, WellKnownRules } from './rule.js';
import { State } from './state.js';
class Cell {
/**
* Subject used hold and emit current state to subscribers
* @type {BehaviorSubject<State>}
*/
#stateSubject;
/**
* A list of notifiers from neighbor cells
* @type {Observable<State>[]}
*/
#neighbors = [];
/**
* Used to broadcast current position and state whenever a change occurs.
* @type {Subject<[number, number, State]>}
*/
changeEmitter;
/**
* Indicates a next step signal.
* @type {Observable<void>}
*/
#ticker;
/**
* X position within the grid.
* @type {number}
*/
#posX;
/**
* Y position within the grid.
* @type {number}
*/
#posY;
/**
* The neighbor rules for this cell.
* @member {Rule}
*/
#rule;
/**
* @param {Observable<void>} ticker - the game "clock" that emits whenever state should update
* @param {number} x
* @param {number} y
* @param {Subject<[number, number, State]>} changeEmitter
* @param {State} state - initial state, defaults to false
* @param {Rule} rule - the neighbor rules for this cell (defaults to B3/S23 for Game of Life)
*/
constructor(
ticker,
x,
y,
changeEmitter = null,
state = State.DEAD,
rule = WellKnownRules.GAME_OF_LIFE,
) {
this.#ticker = ticker;
this.#posX = x;
this.#posY = y;
this.changeEmitter = changeEmitter;
this.#stateSubject = new BehaviorSubject(state);
this.#rule = rule;
}
/** @returns {State} whether this cell is alive or dead */
get state() {
return this.#stateSubject.getValue();
}
/** @param {State} state - the new state to set and broadcast from this cell */
set state(state) {
this.#stateSubject.next(state);
}
/**
* Add a neighbor listener to this cell's registry.
* @param {Cell} cell
*/
addNeighbor(cell) {
this.#neighbors.push(cell.#stateSubject.asObservable());
}
/**
* Begins listening to neighbor notifications, unsubscribing once
* stopSignal emits.
* On each tick, this cell updates its state and notifies its neighbors.
*
* @param {Observable<void>} stopSignal - unsubscribe notifier
* @returns {Subscription}
*/
start(stopSignal) {
return this.listenUntil(stopSignal).subscribe({
next: (state) => this.#stateSubject.next(state),
error: (err) =>
console.error(`Error in cell ${this.#posX},${this.#posY}: ${err}`),
});
}
/**
* Returns an observable that updates its state on each tick, based on
* the states emitted from neighbor cells.
*
* @param {Observable<void>} stopSignal - unsubscribe notifier
* @return {Observable<State>} the next state of this cell
*/
listenUntil(stopSignal) {
return zip(this.#neighbors).pipe(
sample(this.#ticker),
map((states) => states.filter((state) => state === State.ALIVE).length),
switchMap((neighborCount) => this.#updateState(neighborCount)),
takeUntil(stopSignal),
);
}
/**
* Returns true (alive) or false (dead) for the next state based on number of
* living neighbor cells.
*
* @param livingNeighborCount {number} number of living neighbors
* @returns {State}
*/
#nextState(livingNeighborCount) {
if (
this.state.isAlive &&
this.#rule.survivalCounts.includes(livingNeighborCount)
)
return State.ALIVE;
if (
!(
this.state.isDead &&
this.#rule.birthCounts.includes(livingNeighborCount)
)
) {
return State.DEAD;
}
return State.ALIVE;
}
/**
* Updates this cell's state and returns it wrapped in an observable.
* Also publishes coords and state in the event of a change.
*
* @param livingNeighborCount {number}
* @return {Observable<State>}
*/
#updateState(livingNeighborCount) {
const prev = this.state;
this.state = this.#nextState(livingNeighborCount);
if (prev !== this.state) {
this.changeEmitter.next([this.#posX, this.#posY, this.state]);
}
return of(this.state);
}
toString() {
return `Cell(${this.#posX},${this.#posY}): ${this.state}`;
}
}
export { Cell };
|