import {
  type WalletInterface,
  type WalletNotification,
  type NotificationHolderInterface,
} from './generated/bark';

type Unsubscribe = () => void;

/**
 * Wraps the pull-based {@link NotificationHolderInterface} into a subscribe/unsubscribe API.
 *
 * The internal polling loop starts when the first listener subscribes and stops when the
 * last listener unsubscribes.  Re-subscribing after all listeners have been removed creates
 * a fresh {@link NotificationHolderInterface} and restarts the loop.
 *
 * @example
 * ```ts
 * const notifications = new WalletNotifications(wallet);
 *
 * const unsubscribe = notifications.subscribe((event) => {
 *   switch (event.tag) {
 *     case WalletNotification_Tags.MovementCreated:
 *       console.log('movement created', event.inner.movement);
 *       break;
 *     case WalletNotification_Tags.MovementUpdated:
 *       console.log('movement updated', event.inner.movement);
 *       break;
 *     case WalletNotification_Tags.ChannelLagging:
 *       console.log('channel lagging');
 *       break;
 *   }
 * });
 *
 * // later…
 * unsubscribe();
 * ```
 */
export class WalletNotifications {
  private holder: NotificationHolderInterface | null = null;
  private readonly listeners = new Set<(event: WalletNotification) => void>();

  constructor(private readonly wallet: WalletInterface) {}

  subscribe(listener: (event: WalletNotification) => void): Unsubscribe {
    this.listeners.add(listener);

    if (this.listeners.size === 1) {
      this.startLoop();
    }

    return () => {
      this.listeners.delete(listener);
      if (this.listeners.size === 0) {
        this.holder?.cancelNextNotificationWait();
        this.holder = null;
      }
    };
  }

  private startLoop(): void {
    const localHolder = this.wallet.notifications();
    this.holder = localHolder;

    (async () => {
      try {
        while (true) {
          const event = await localHolder.nextNotification();
          if (event == null) break;
          for (const listener of this.listeners) {
            try {
              listener(event);
            } catch (err) {
              console.error('Wallet notification listener failed', err);
            }
          }
        }
      } catch (err) {
        console.error('Wallet notification loop failed', err);
      } finally {
        if (this.holder === localHolder) {
          this.holder = null;
        }
      }
    })();
  }
}