IEventLocker.ts

import type { IEvent } from './IEvent.ts';
import { isObject } from './isObject.ts';

/**
 * Interface for tracking event processing state to prevent concurrent processing
 * by multiple processes.
 */
export interface IEventLocker {

	/**
	 * Retrieves the last projected event,
	 * allowing the projection state to be restored from subsequent events.
	 */
	getLastEvent(): Promise<IEvent | undefined> | IEvent | undefined;

	/**
	 * Marks an event as projecting to prevent it from being processed
	 * by another projection instance using the same storage.
	 *
	 * @returns `false` if the event is already being processed or has been processed.
	 */
	tryMarkAsProjecting(event: IEvent): Promise<boolean> | boolean;

	/**
	 * Marks an event as projected.
	 */
	markAsProjected(event: IEvent): Promise<void> | void;

	/**
	 * Records an event as the last projected event (restore checkpoint).
	 */
	markAsLastEvent(event: IEvent): Promise<void> | void;
}

export const isEventLocker = (view: unknown): view is IEventLocker =>
	(
		isObject(view)
		&& 'getLastEvent' in view
		&& 'tryMarkAsProjecting' in view
		&& 'markAsProjected' in view
		&& 'markAsLastEvent' in view
	) || (
		typeof view === 'function'
		&& typeof (view as any).getLastEvent === 'function'
		&& typeof (view as any).tryMarkAsProjecting === 'function'
		&& typeof (view as any).markAsProjected === 'function'
		&& typeof (view as any).markAsLastEvent === 'function'
	);