--- /dev/null
+import { PartialObserver } from './types';
+import { Observable } from './Observable';
+import { empty } from './observable/empty';
+import { of } from './observable/of';
+import { throwError } from './observable/throwError';
+import { deprecate } from 'util';
+
+// TODO: When this enum is removed, replace it with a type alias. See #4556.
+/**
+ * @deprecated NotificationKind is deprecated as const enums are not compatible with isolated modules. Use a string literal instead.
+ */
+export enum NotificationKind {
+ NEXT = 'N',
+ ERROR = 'E',
+ COMPLETE = 'C',
+}
+
+/**
+ * Represents a push-based event or value that an {@link Observable} can emit.
+ * This class is particularly useful for operators that manage notifications,
+ * like {@link materialize}, {@link dematerialize}, {@link observeOn}, and
+ * others. Besides wrapping the actual delivered value, it also annotates it
+ * with metadata of, for instance, what type of push message it is (`next`,
+ * `error`, or `complete`).
+ *
+ * @see {@link materialize}
+ * @see {@link dematerialize}
+ * @see {@link observeOn}
+ *
+ * @class Notification<T>
+ */
+export class Notification<T> {
+ hasValue: boolean;
+
+ constructor(public kind: 'N' | 'E' | 'C', public value?: T, public error?: any) {
+ this.hasValue = kind === 'N';
+ }
+
+ /**
+ * Delivers to the given `observer` the value wrapped by this Notification.
+ * @param {Observer} observer
+ * @return
+ */
+ observe(observer: PartialObserver<T>): any {
+ switch (this.kind) {
+ case 'N':
+ return observer.next && observer.next(this.value);
+ case 'E':
+ return observer.error && observer.error(this.error);
+ case 'C':
+ return observer.complete && observer.complete();
+ }
+ }
+
+ /**
+ * Given some {@link Observer} callbacks, deliver the value represented by the
+ * current Notification to the correctly corresponding callback.
+ * @param {function(value: T): void} next An Observer `next` callback.
+ * @param {function(err: any): void} [error] An Observer `error` callback.
+ * @param {function(): void} [complete] An Observer `complete` callback.
+ * @return {any}
+ */
+ do(next: (value: T) => void, error?: (err: any) => void, complete?: () => void): any {
+ const kind = this.kind;
+ switch (kind) {
+ case 'N':
+ return next && next(this.value);
+ case 'E':
+ return error && error(this.error);
+ case 'C':
+ return complete && complete();
+ }
+ }
+
+ /**
+ * Takes an Observer or its individual callback functions, and calls `observe`
+ * or `do` methods accordingly.
+ * @param {Observer|function(value: T): void} nextOrObserver An Observer or
+ * the `next` callback.
+ * @param {function(err: any): void} [error] An Observer `error` callback.
+ * @param {function(): void} [complete] An Observer `complete` callback.
+ * @return {any}
+ */
+ accept(nextOrObserver: PartialObserver<T> | ((value: T) => void), error?: (err: any) => void, complete?: () => void) {
+ if (nextOrObserver && typeof (<PartialObserver<T>>nextOrObserver).next === 'function') {
+ return this.observe(<PartialObserver<T>>nextOrObserver);
+ } else {
+ return this.do(<(value: T) => void>nextOrObserver, error, complete);
+ }
+ }
+
+ /**
+ * Returns a simple Observable that just delivers the notification represented
+ * by this Notification instance.
+ * @return {any}
+ */
+ toObservable(): Observable<T> {
+ const kind = this.kind;
+ switch (kind) {
+ case 'N':
+ return of(this.value);
+ case 'E':
+ return throwError(this.error);
+ case 'C':
+ return empty();
+ }
+ throw new Error('unexpected notification kind value');
+ }
+
+ private static completeNotification: Notification<any> = new Notification('C');
+ private static undefinedValueNotification: Notification<any> = new Notification('N', undefined);
+
+ /**
+ * A shortcut to create a Notification instance of the type `next` from a
+ * given value.
+ * @param {T} value The `next` value.
+ * @return {Notification<T>} The "next" Notification representing the
+ * argument.
+ * @nocollapse
+ */
+ static createNext<T>(value: T): Notification<T> {
+ if (typeof value !== 'undefined') {
+ return new Notification('N', value);
+ }
+ return Notification.undefinedValueNotification;
+ }
+
+ /**
+ * A shortcut to create a Notification instance of the type `error` from a
+ * given error.
+ * @param {any} [err] The `error` error.
+ * @return {Notification<T>} The "error" Notification representing the
+ * argument.
+ * @nocollapse
+ */
+ static createError<T>(err?: any): Notification<T> {
+ return new Notification('E', undefined, err);
+ }
+
+ /**
+ * A shortcut to create a Notification instance of the type `complete`.
+ * @return {Notification<any>} The valueless "complete" Notification.
+ * @nocollapse
+ */
+ static createComplete(): Notification<any> {
+ return Notification.completeNotification;
+ }
+}