/** @license for symbol-observable
 *  The MIT License (MIT)
 *
 *  Copyright (c) Sindre Sorhus <sindresorhus@gmail.com> (sindresorhus.com)
 *  Copyright (c) Ben Lesh <ben@benlesh.com>
 *
 *  Permission is hereby granted, free of charge, to any person obtaining a copy
 *  of this software and associated documentation files (the "Software"), to deal
 *  in the Software without restriction, including without limitation the rights
 *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 *  copies of the Software, and to permit persons to whom the Software is
 *  furnished to do so, subject to the following conditions:
 *
 *  The above copyright notice and this permission notice shall be included in
 *  all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 *  THE SOFTWARE.
 */
function symbolObservablePonyfill(root) {
	var result;
	var Symbol = root.Symbol;

	if (typeof Symbol === 'function') {
		if (Symbol.observable) {
			result = Symbol.observable;
		} else {
			result = Symbol('observable');
			Symbol.observable = result;
		}
	} else {
		result = '@@observable';
	}

	return result;
}

/* global window */

var root;

if (typeof self !== 'undefined') {
  root = self;
} else if (typeof window !== 'undefined') {
  root = window;
} else if (typeof global !== 'undefined') {
  root = global;
} else if (typeof module !== 'undefined') {
  root = module;
} else {
  root = Function('return this')();
}

var $observable = symbolObservablePonyfill(root);

/** @license
 *  Copyright 2016 - present The Material Motion Authors. All Rights Reserved.
 *
 *  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.
 */
/**
 * TypeScript is a pain to use with polymorphic types unless you wrap them in a
 * function that returns a single type.  So, that's what this is.
 *
 * If you give it an observer, you get back that observer.  If you give it an
 * anonymous function, you get back that anonymous function wrapped in an
 * observer.
 */
function wrapWithObserver(listener) {
    if (typeof listener === 'function') {
        return {
            next: listener
        };
    }
    else {
        return listener;
    }
}


/**
 * `Observable` is a standard interface that's useful for modeling multiple,
 * asynchronous events.
 *
 * `IndefiniteObservable` is a minimalist implementation of a subset of the TC39
 * Observable proposal.  It is indefinite because it will never call `complete`
 * or `error` on the provided observer.
 */
class IndefiniteObservable {
    /**
     * The provided function should receive an observer and connect that
     * observer's `next` method to an event source (for instance,
     * `element.addEventListener('click', observer.next)`).
     *
     * It must return a function that will disconnect the observer from the event
     * source.
     */
    constructor(connect) {
        this._connect = connect;
    }
    /**
     * `subscribe` uses the function supplied to the constructor to connect an
     * observer to an event source.  Each observer is connected independently:
     * each call to `subscribe` calls `connect` with the new observer.
     *
     * To disconnect the observer from the event source, call `unsubscribe` on the
     * returned subscription.
     *
     * Note: `subscribe` accepts either a function or an object with a
     * next method.
     */
    subscribe(observerOrNext) {
        // For simplicity's sake, `subscribe` accepts `next` either as either an
        // anonymous function or wrapped in an object (the observer).  Since
        // `connect` always expects to receive an observer, wrap any loose
        // functions in an object.
        const observer = wrapWithObserver(observerOrNext);
        let disconnect = this._connect(observer);
        return {
            unsubscribe() {
                if (disconnect) {
                    disconnect();
                    disconnect = undefined;
                }
            }
        };
    }
    /**
     * Tells other libraries that know about observables that we are one.
     *
     * https://github.com/tc39/proposal-observable#observable
     */
    [$observable]() {
        return this;
    }
}



export { wrapWithObserver, IndefiniteObservable };
export default IndefiniteObservable;