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server/node_modules/graphql/subscription/mapAsyncIterator.js.flow

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+/**
+ * Copyright (c) 2017-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ */
+
+import { $$asyncIterator, getAsyncIterator } from 'iterall';
+import type { MaybePromise } from '../jsutils/MaybePromise';
+
+/**
+ * Given an AsyncIterable and a callback function, return an AsyncIterator
+ * which produces values mapped via calling the callback function.
+ */
+export default function mapAsyncIterator<T, U>(
+  iterable: AsyncIterable<T>,
+  callback: T => MaybePromise<U>,
+  rejectCallback?: any => MaybePromise<U>,
+): AsyncGenerator<U, void, void> {
+  const iterator = getAsyncIterator(iterable);
+  let $return;
+  let abruptClose;
+  // $FlowFixMe(>=0.68.0)
+  if (typeof iterator.return === 'function') {
+    $return = iterator.return;
+    abruptClose = error => {
+      const rethrow = () => Promise.reject(error);
+      return $return.call(iterator).then(rethrow, rethrow);
+    };
+  }
+
+  function mapResult(result) {
+    return result.done
+      ? result
+      : asyncMapValue(result.value, callback).then(iteratorResult, abruptClose);
+  }
+
+  let mapReject;
+  if (rejectCallback) {
+    // Capture rejectCallback to ensure it cannot be null.
+    const reject = rejectCallback;
+    mapReject = error =>
+      asyncMapValue(error, reject).then(iteratorResult, abruptClose);
+  }
+
+  /* TODO: Flow doesn't support symbols as keys:
+     https://github.com/facebook/flow/issues/3258 */
+  return ({
+    next() {
+      return iterator.next().then(mapResult, mapReject);
+    },
+    return() {
+      return $return
+        ? $return.call(iterator).then(mapResult, mapReject)
+        : Promise.resolve({ value: undefined, done: true });
+    },
+    throw(error) {
+      // $FlowFixMe(>=0.68.0)
+      if (typeof iterator.throw === 'function') {
+        return iterator.throw(error).then(mapResult, mapReject);
+      }
+      return Promise.reject(error).catch(abruptClose);
+    },
+    [$$asyncIterator]() {
+      return this;
+    },
+  }: any);
+}
+
+function asyncMapValue<T, U>(
+  value: T,
+  callback: T => MaybePromise<U>,
+): Promise<U> {
+  return new Promise(resolve => resolve(callback(value)));
+}
+
+function iteratorResult<T>(value: T): IteratorResult<T, void> {
+  return { value, done: false };
+}