// (C) Copyright 2015 Moodle Pty Ltd.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import { EventEmitter } from '@angular/core';
import { Observable } from 'rxjs';

/**
 * Subscribable object.
 */
type Subscribable<T> = EventEmitter<T> | Observable<T>;

/**
 * Singleton with helpers to work with subscriptions.
 */
export class CoreSubscriptions {

    /**
     * Listen once to a subscribable object.
     *
     * @param subscribable Subscribable to listen to.
     * @param onSuccess Callback to run when the subscription is updated.
     * @param onError Callback to run when the an error happens.
     */
    static once<T>(subscribable: Subscribable<T>, onSuccess: (value: T) => unknown, onError?: (error: unknown) => unknown): void {
        const subscription = subscribable.subscribe(
            value => {
                // Unsubscribe using a timeout because we can receive a value immediately.
                setTimeout(() => subscription.unsubscribe(), 0);

                onSuccess(value);
            },
            error => {
                // Unsubscribe using a timeout because we can receive a value immediately.
                setTimeout(() => subscription.unsubscribe(), 0);

                onError && onError(error);
            },
        );
    }

}