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node_modules/rxjs/src/internal/operators/mergeMap.ts

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+import { Observable } from '../Observable';
+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { Subscription } from '../Subscription';
+import { subscribeToResult } from '../util/subscribeToResult';
+import { OuterSubscriber } from '../OuterSubscriber';
+import { InnerSubscriber } from '../InnerSubscriber';
+import { ObservableInput, OperatorFunction, ObservedValueOf } from '../types';
+import { map } from './map';
+import { from } from '../observable/from';
+
+/* tslint:disable:max-line-length */
+export function mergeMap<T, O extends ObservableInput<any>>(project: (value: T, index: number) => O, concurrent?: number): OperatorFunction<T, ObservedValueOf<O>>;
+/** @deprecated resultSelector no longer supported, use inner map instead */
+export function mergeMap<T, O extends ObservableInput<any>>(project: (value: T, index: number) => O, resultSelector: undefined, concurrent?: number): OperatorFunction<T, ObservedValueOf<O>>;
+/** @deprecated resultSelector no longer supported, use inner map instead */
+export function mergeMap<T, R, O extends ObservableInput<any>>(project: (value: T, index: number) => O, resultSelector: (outerValue: T, innerValue: ObservedValueOf<O>, outerIndex: number, innerIndex: number) => R, concurrent?: number): OperatorFunction<T, R>;
+/* tslint:enable:max-line-length */
+
+/**
+ * Projects each source value to an Observable which is merged in the output
+ * Observable.
+ *
+ * <span class="informal">Maps each value to an Observable, then flattens all of
+ * these inner Observables using {@link mergeAll}.</span>
+ *
+ * ![](mergeMap.png)
+ *
+ * Returns an Observable that emits items based on applying a function that you
+ * supply to each item emitted by the source Observable, where that function
+ * returns an Observable, and then merging those resulting Observables and
+ * emitting the results of this merger.
+ *
+ * ## Example
+ * Map and flatten each letter to an Observable ticking every 1 second
+ * ```ts
+ * import { of, interval } from 'rxjs';
+ * import { mergeMap, map } from 'rxjs/operators';
+ *
+ * const letters = of('a', 'b', 'c');
+ * const result = letters.pipe(
+ *   mergeMap(x => interval(1000).pipe(map(i => x+i))),
+ * );
+ * result.subscribe(x => console.log(x));
+ *
+ * // Results in the following:
+ * // a0
+ * // b0
+ * // c0
+ * // a1
+ * // b1
+ * // c1
+ * // continues to list a,b,c with respective ascending integers
+ * ```
+ *
+ * @see {@link concatMap}
+ * @see {@link exhaustMap}
+ * @see {@link merge}
+ * @see {@link mergeAll}
+ * @see {@link mergeMapTo}
+ * @see {@link mergeScan}
+ * @see {@link switchMap}
+ *
+ * @param {function(value: T, ?index: number): ObservableInput} project A function
+ * that, when applied to an item emitted by the source Observable, returns an
+ * Observable.
+ * @param {number} [concurrent=Number.POSITIVE_INFINITY] Maximum number of input
+ * Observables being subscribed to concurrently.
+ * @return {Observable} An Observable that emits the result of applying the
+ * projection function (and the optional deprecated `resultSelector`) to each item
+ * emitted by the source Observable and merging the results of the Observables
+ * obtained from this transformation.
+ * @method mergeMap
+ * @owner Observable
+ */
+export function mergeMap<T, R, O extends ObservableInput<any>>(
+  project: (value: T, index: number) => O,
+  resultSelector?: ((outerValue: T, innerValue: ObservedValueOf<O>, outerIndex: number, innerIndex: number) => R) | number,
+  concurrent: number = Number.POSITIVE_INFINITY
+): OperatorFunction<T, ObservedValueOf<O>|R> {
+  if (typeof resultSelector === 'function') {
+    // DEPRECATED PATH
+    return (source: Observable<T>) => source.pipe(
+      mergeMap((a, i) => from(project(a, i)).pipe(
+        map((b: any, ii: number) => resultSelector(a, b, i, ii)),
+      ), concurrent)
+    );
+  } else if (typeof resultSelector === 'number') {
+    concurrent = resultSelector;
+  }
+  return (source: Observable<T>) => source.lift(new MergeMapOperator(project, concurrent));
+}
+
+export class MergeMapOperator<T, R> implements Operator<T, R> {
+  constructor(private project: (value: T, index: number) => ObservableInput<R>,
+              private concurrent: number = Number.POSITIVE_INFINITY) {
+  }
+
+  call(observer: Subscriber<R>, source: any): any {
+    return source.subscribe(new MergeMapSubscriber(
+      observer, this.project, this.concurrent
+    ));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+export class MergeMapSubscriber<T, R> extends OuterSubscriber<T, R> {
+  private hasCompleted: boolean = false;
+  private buffer: T[] = [];
+  private active: number = 0;
+  protected index: number = 0;
+
+  constructor(destination: Subscriber<R>,
+              private project: (value: T, index: number) => ObservableInput<R>,
+              private concurrent: number = Number.POSITIVE_INFINITY) {
+    super(destination);
+  }
+
+  protected _next(value: T): void {
+    if (this.active < this.concurrent) {
+      this._tryNext(value);
+    } else {
+      this.buffer.push(value);
+    }
+  }
+
+  protected _tryNext(value: T) {
+    let result: ObservableInput<R>;
+    const index = this.index++;
+    try {
+      result = this.project(value, index);
+    } catch (err) {
+      this.destination.error(err);
+      return;
+    }
+    this.active++;
+    this._innerSub(result, value, index);
+  }
+
+  private _innerSub(ish: ObservableInput<R>, value: T, index: number): void {
+    const innerSubscriber = new InnerSubscriber(this, value, index);
+    const destination = this.destination as Subscription;
+    destination.add(innerSubscriber);
+    const innerSubscription = subscribeToResult<T, R>(this, ish, undefined, undefined, innerSubscriber);
+    // The returned subscription will usually be the subscriber that was
+    // passed. However, interop subscribers will be wrapped and for
+    // unsubscriptions to chain correctly, the wrapper needs to be added, too.
+    if (innerSubscription !== innerSubscriber) {
+      destination.add(innerSubscription);
+    }
+  }
+
+  protected _complete(): void {
+    this.hasCompleted = true;
+    if (this.active === 0 && this.buffer.length === 0) {
+      this.destination.complete();
+    }
+    this.unsubscribe();
+  }
+
+  notifyNext(outerValue: T, innerValue: R,
+             outerIndex: number, innerIndex: number,
+             innerSub: InnerSubscriber<T, R>): void {
+    this.destination.next(innerValue);
+  }
+
+  notifyComplete(innerSub: Subscription): void {
+    const buffer = this.buffer;
+    this.remove(innerSub);
+    this.active--;
+    if (buffer.length > 0) {
+      this._next(buffer.shift());
+    } else if (this.active === 0 && this.hasCompleted) {
+      this.destination.complete();
+    }
+  }
+}