/**
 * Tracks which socket.io connection ids are subscribed to each logical channel.
 * Keys: "patch:<patchId>", "waterTank", "power", "wateringSessions", "waterSchedules"
 */
export class SubscriptionRegistry {
  constructor() {
    /** @type {Map<string, Set<string>>} */
    this._keyToSockets = new Map();
    /** @type {Map<string, Set<string>>} */
    this._socketToKeys = new Map();
  }

  static channelKey(resource, id) {
    if (resource === "patch") {
      if (id == null || id === "") return null;
      return `patch:${id}`;
    }
    if (resource === "waterTank") return "waterTank";
    if (resource === "power") return "power";
    if (resource === "wateringSessions") return "wateringSessions";
    if (resource === "waterSchedules") return "waterSchedules";
    return null;
  }

  subscribe(socketId, key) {
    if (!key) return;
    if (!this._keyToSockets.has(key)) this._keyToSockets.set(key, new Set());
    this._keyToSockets.get(key).add(socketId);
    if (!this._socketToKeys.has(socketId)) this._socketToKeys.set(socketId, new Set());
    this._socketToKeys.get(socketId).add(key);
  }

  unsubscribe(socketId, key) {
    if (!key) return;
    this._keyToSockets.get(key)?.delete(socketId);
    if (this._keyToSockets.get(key)?.size === 0) {
      this._keyToSockets.delete(key);
    }
    this._socketToKeys.get(socketId)?.delete(key);
    if (this._socketToKeys.get(socketId)?.size === 0) {
      this._socketToKeys.delete(socketId);
    }
  }

  removeSocket(socketId) {
    const keys = this._socketToKeys.get(socketId);
    if (!keys) return;
    for (const key of keys) {
      this._keyToSockets.get(key)?.delete(socketId);
      if (this._keyToSockets.get(key)?.size === 0) {
        this._keyToSockets.delete(key);
      }
    }
    this._socketToKeys.delete(socketId);
  }

  /** @returns {Iterable<string>} */
  getSubscriberIds(key) {
    return this._keyToSockets.get(key) ?? [];
  }
}