/**
 * Copyright 2019 Google Inc. 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.
 */ import { Observable , Transform } from "../types.js" ; import { externalPromise } from "../utils.js" ; typeparam returns export function exhaust < T > ( ) { const lastInnerDone = externalPromise ( ) ; let outerDone = false ; const { readable , writable } = new TransformStream < Observable < T > , Observable < T > > ( undefined , { highWaterMark : 1 } , { highWaterMark : 0 } ) ; let currentReader ; return { writable , readable : new ReadableStream < T > ( { async start ( controller ) { const reader = readable . getReader ( ) ; while ( true ) { const { value , done } = await reader . read ( ) ; if ( done ) { outerDone = true ; if ( currentReader ) { await lastInnerDone . promise ; } controller . close ( ) ; return ; } if ( currentReader ) { continue ; } currentReader = value ! . getReader ( ) ; ( async ( ) => { const readerCopy = currentReader ; while ( true ) { const { value , done } = await readerCopy ! . read ( ) ; if ( done ) { if ( outerDone ) { lastInnerDone . resolve ( ) ; } currentReader = null ; return ; } controller . enqueue ( value ! ) ; } } ) ( ) ; } } } , { highWaterMark : 0 } ) } ; }