initial commit: scaffolding

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diff --git a/node_modules/rxjs/src/internal/operators/groupBy.ts b/node_modules/rxjs/src/internal/operators/groupBy.ts
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+import { Observable } from '../Observable';
+import { innerFrom } from '../observable/innerFrom';
+import { Subject } from '../Subject';
+import { ObservableInput, Observer, OperatorFunction, SubjectLike } from '../types';
+import { operate } from '../util/lift';
+import { createOperatorSubscriber, OperatorSubscriber } from './OperatorSubscriber';
+
+export interface BasicGroupByOptions<K, T> {
+  element?: undefined;
+  duration?: (grouped: GroupedObservable<K, T>) => ObservableInput<any>;
+  connector?: () => SubjectLike<T>;
+}
+
+export interface GroupByOptionsWithElement<K, E, T> {
+  element: (value: T) => E;
+  duration?: (grouped: GroupedObservable<K, E>) => ObservableInput<any>;
+  connector?: () => SubjectLike<E>;
+}
+
+export function groupBy<T, K>(key: (value: T) => K, options: BasicGroupByOptions<K, T>): OperatorFunction<T, GroupedObservable<K, T>>;
+
+export function groupBy<T, K, E>(
+  key: (value: T) => K,
+  options: GroupByOptionsWithElement<K, E, T>
+): OperatorFunction<T, GroupedObservable<K, E>>;
+
+export function groupBy<T, K extends T>(
+  key: (value: T) => value is K
+): OperatorFunction<T, GroupedObservable<true, K> | GroupedObservable<false, Exclude<T, K>>>;
+
+export function groupBy<T, K>(key: (value: T) => K): OperatorFunction<T, GroupedObservable<K, T>>;
+
+/**
+ * @deprecated use the options parameter instead.
+ */
+export function groupBy<T, K>(
+  key: (value: T) => K,
+  element: void,
+  duration: (grouped: GroupedObservable<K, T>) => Observable<any>
+): OperatorFunction<T, GroupedObservable<K, T>>;
+
+/**
+ * @deprecated use the options parameter instead.
+ */
+export function groupBy<T, K, R>(
+  key: (value: T) => K,
+  element?: (value: T) => R,
+  duration?: (grouped: GroupedObservable<K, R>) => Observable<any>
+): OperatorFunction<T, GroupedObservable<K, R>>;
+
+/**
+ * Groups the items emitted by an Observable according to a specified criterion,
+ * and emits these grouped items as `GroupedObservables`, one
+ * {@link GroupedObservable} per group.
+ *
+ * ![](groupBy.png)
+ *
+ * When the Observable emits an item, a key is computed for this item with the key function.
+ *
+ * If a {@link GroupedObservable} for this key exists, this {@link GroupedObservable} emits. Otherwise, a new
+ * {@link GroupedObservable} for this key is created and emits.
+ *
+ * A {@link GroupedObservable} represents values belonging to the same group represented by a common key. The common
+ * key is available as the `key` field of a {@link GroupedObservable} instance.
+ *
+ * The elements emitted by {@link GroupedObservable}s are by default the items emitted by the Observable, or elements
+ * returned by the element function.
+ *
+ * ## Examples
+ *
+ * Group objects by `id` and return as array
+ *
+ * ```ts
+ * import { of, groupBy, mergeMap, reduce } from 'rxjs';
+ *
+ * of(
+ *   { id: 1, name: 'JavaScript' },
+ *   { id: 2, name: 'Parcel' },
+ *   { id: 2, name: 'webpack' },
+ *   { id: 1, name: 'TypeScript' },
+ *   { id: 3, name: 'TSLint' }
+ * ).pipe(
+ *   groupBy(p => p.id),
+ *   mergeMap(group$ => group$.pipe(reduce((acc, cur) => [...acc, cur], [])))
+ * )
+ * .subscribe(p => console.log(p));
+ *
+ * // displays:
+ * // [{ id: 1, name: 'JavaScript' }, { id: 1, name: 'TypeScript'}]
+ * // [{ id: 2, name: 'Parcel' }, { id: 2, name: 'webpack'}]
+ * // [{ id: 3, name: 'TSLint' }]
+ * ```
+ *
+ * Pivot data on the `id` field
+ *
+ * ```ts
+ * import { of, groupBy, mergeMap, reduce, map } from 'rxjs';
+ *
+ * of(
+ *   { id: 1, name: 'JavaScript' },
+ *   { id: 2, name: 'Parcel' },
+ *   { id: 2, name: 'webpack' },
+ *   { id: 1, name: 'TypeScript' },
+ *   { id: 3, name: 'TSLint' }
+ * ).pipe(
+ *   groupBy(p => p.id, { element: p => p.name }),
+ *   mergeMap(group$ => group$.pipe(reduce((acc, cur) => [...acc, cur], [`${ group$.key }`]))),
+ *   map(arr => ({ id: parseInt(arr[0], 10), values: arr.slice(1) }))
+ * )
+ * .subscribe(p => console.log(p));
+ *
+ * // displays:
+ * // { id: 1, values: [ 'JavaScript', 'TypeScript' ] }
+ * // { id: 2, values: [ 'Parcel', 'webpack' ] }
+ * // { id: 3, values: [ 'TSLint' ] }
+ * ```
+ *
+ * @param key A function that extracts the key
+ * for each item.
+ * @param element A function that extracts the
+ * return element for each item.
+ * @param duration
+ * A function that returns an Observable to determine how long each group should
+ * exist.
+ * @param connector Factory function to create an
+ * intermediate Subject through which grouped elements are emitted.
+ * @return A function that returns an Observable that emits GroupedObservables,
+ * each of which corresponds to a unique key value and each of which emits
+ * those items from the source Observable that share that key value.
+ *
+ * @deprecated Use the options parameter instead.
+ */
+export function groupBy<T, K, R>(
+  key: (value: T) => K,
+  element?: (value: T) => R,
+  duration?: (grouped: GroupedObservable<K, R>) => Observable<any>,
+  connector?: () => Subject<R>
+): OperatorFunction<T, GroupedObservable<K, R>>;
+
+// Impl
+export function groupBy<T, K, R>(
+  keySelector: (value: T) => K,
+  elementOrOptions?: ((value: any) => any) | void | BasicGroupByOptions<K, T> | GroupByOptionsWithElement<K, R, T>,
+  duration?: (grouped: GroupedObservable<any, any>) => ObservableInput<any>,
+  connector?: () => SubjectLike<any>
+): OperatorFunction<T, GroupedObservable<K, R>> {
+  return operate((source, subscriber) => {
+    let element: ((value: any) => any) | void;
+    if (!elementOrOptions || typeof elementOrOptions === 'function') {
+      element = elementOrOptions as ((value: any) => any);
+    } else {
+      ({ duration, element, connector } = elementOrOptions);
+    }
+
+    // A lookup for the groups that we have so far.
+    const groups = new Map<K, SubjectLike<any>>();
+
+    // Used for notifying all groups and the subscriber in the same way.
+    const notify = (cb: (group: Observer<any>) => void) => {
+      groups.forEach(cb);
+      cb(subscriber);
+    };
+
+    // Used to handle errors from the source, AND errors that occur during the
+    // next call from the source.
+    const handleError = (err: any) => notify((consumer) => consumer.error(err));
+
+    // The number of actively subscribed groups
+    let activeGroups = 0;
+
+    // Whether or not teardown was attempted on this subscription.
+    let teardownAttempted = false;
+
+    // Capturing a reference to this, because we need a handle to it
+    // in `createGroupedObservable` below. This is what we use to
+    // subscribe to our source observable. This sometimes needs to be unsubscribed
+    // out-of-band with our `subscriber` which is the downstream subscriber, or destination,
+    // in cases where a user unsubscribes from the main resulting subscription, but
+    // still has groups from this subscription subscribed and would expect values from it
+    // Consider:  `source.pipe(groupBy(fn), take(2))`.
+    const groupBySourceSubscriber = new OperatorSubscriber(
+      subscriber,
+      (value: T) => {
+        // Because we have to notify all groups of any errors that occur in here,
+        // we have to add our own try/catch to ensure that those errors are propagated.
+        // OperatorSubscriber will only send the error to the main subscriber.
+        try {
+          const key = keySelector(value);
+
+          let group = groups.get(key);
+          if (!group) {
+            // Create our group subject
+            groups.set(key, (group = connector ? connector() : new Subject<any>()));
+
+            // Emit the grouped observable. Note that we can't do a simple `asObservable()` here,
+            // because the grouped observable has special semantics around reference counting
+            // to ensure we don't sever our connection to the source prematurely.
+            const grouped = createGroupedObservable(key, group);
+            subscriber.next(grouped);
+
+            if (duration) {
+              const durationSubscriber = createOperatorSubscriber(
+                // Providing the group here ensures that it is disposed of -- via `unsubscribe` --
+                // when the duration subscription is torn down. That is important, because then
+                // if someone holds a handle to the grouped observable and tries to subscribe to it
+                // after the connection to the source has been severed, they will get an
+                // `ObjectUnsubscribedError` and know they can't possibly get any notifications.
+                group as any,
+                () => {
+                  // Our duration notified! We can complete the group.
+                  // The group will be removed from the map in the finalization phase.
+                  group!.complete();
+                  durationSubscriber?.unsubscribe();
+                },
+                // Completions are also sent to the group, but just the group.
+                undefined,
+                // Errors on the duration subscriber are sent to the group
+                // but only the group. They are not sent to the main subscription.
+                undefined,
+                // Finalization: Remove this group from our map.
+                () => groups.delete(key)
+              );
+
+              // Start our duration notifier.
+              groupBySourceSubscriber.add(innerFrom(duration(grouped)).subscribe(durationSubscriber));
+            }
+          }
+
+          // Send the value to our group.
+          group.next(element ? element(value) : value);
+        } catch (err) {
+          handleError(err);
+        }
+      },
+      // Source completes.
+      () => notify((consumer) => consumer.complete()),
+      // Error from the source.
+      handleError,
+      // Free up memory.
+      // When the source subscription is _finally_ torn down, release the subjects and keys
+      // in our groups Map, they may be quite large and we don't want to keep them around if we
+      // don't have to.
+      () => groups.clear(),
+      () => {
+        teardownAttempted = true;
+        // We only kill our subscription to the source if we have
+        // no active groups. As stated above, consider this scenario:
+        // source$.pipe(groupBy(fn), take(2)).
+        return activeGroups === 0;
+      }
+    );
+
+    // Subscribe to the source
+    source.subscribe(groupBySourceSubscriber);
+
+    /**
+     * Creates the actual grouped observable returned.
+     * @param key The key of the group
+     * @param groupSubject The subject that fuels the group
+     */
+    function createGroupedObservable(key: K, groupSubject: SubjectLike<any>) {
+      const result: any = new Observable<T>((groupSubscriber) => {
+        activeGroups++;
+        const innerSub = groupSubject.subscribe(groupSubscriber);
+        return () => {
+          innerSub.unsubscribe();
+          // We can kill the subscription to our source if we now have no more
+          // active groups subscribed, and a finalization was already attempted on
+          // the source.
+          --activeGroups === 0 && teardownAttempted && groupBySourceSubscriber.unsubscribe();
+        };
+      });
+      result.key = key;
+      return result;
+    }
+  });
+}
+
+/**
+ * An observable of values that is the emitted by the result of a {@link groupBy} operator,
+ * contains a `key` property for the grouping.
+ */
+export interface GroupedObservable<K, T> extends Observable<T> {
+  /**
+   * The key value for the grouped notifications.
+   */
+  readonly key: K;
+}