// Copyright (c) Cratis. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.

import { FastForwardResult } from './FastForwardResult.js';
import { ObserverInformation } from './ObserverInformation.js';
import { ObserverRemovalResult } from './ObserverRemovalResult.js';

/**
 * Defines a system for working with the observers of an event store.
 */
export interface IObservers {
    /**
     * Gets every observer registered in the event store's current namespace.
     * @returns A collection of {@link ObserverInformation}.
     */
    getAll(): Promise<ObserverInformation[]>;

    /**
     * Removes an observer and everything keyed to it.
     *
     * For the observer whose declaring code is gone - a read model and its projection that were deleted, a
     * reactor that was removed. The observer it registered stays behind, settles into
     * {@link ObserverRunningState.Disconnected} and keeps its records in the event store forever.
     *
     * Removal covers the whole event store, because an observer's definition is a store-level record. It
     * refuses while the observer is running or has a subscribed client in any namespace, so what it can remove
     * is only ever an observer no client is reporting - stop the declaring application first if you mean to
     * remove a live one. Read model data and sink containers are left untouched.
     * @param observerId - The identifier of the observer to remove.
     * @returns An {@link ObserverRemovalResult} describing what happened.
     */
    remove(observerId: string): Promise<ObserverRemovalResult>;

    /**
     * Fast forwards an observer to the tail of the event log, skipping every event it has not yet handled
     * without invoking it. Its failed partitions are discarded. State it has already built is kept, so the
     * effect of the skipped events is missing from it; replay the observer instead to rebuild.
     * @param observerId - The identifier of the observer to fast forward.
     * @returns A {@link FastForwardResult} describing what happened and where the observer is now.
     */
    fastForward(observerId: string): Promise<FastForwardResult>;
}