Add kotlin parallel utilities

/*

 * Copyright (C) 2023 The Android Open Source Project

 *

 * 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.

 */

package com.android.systemui.util.kotlin

import kotlinx.coroutines.CoroutineStart

import kotlinx.coroutines.async

import kotlinx.coroutines.awaitAll

import kotlinx.coroutines.coroutineScope

/** Like [Iterable.flatMap] but executes each [transform] invocation in a separate coroutine. */

suspend fun <A, B> Iterable<A>.flatMapParallel(transform: suspend (A) -> Iterable<B>): List<B> =

    mapParallel(transform).flatten()

/** Like [Iterable.mapNotNull] but executes each [transform] invocation in a separate coroutine. */

suspend fun <A, B> Iterable<A>.mapNotNullParallel(transform: suspend (A) -> B?): List<B> =

    mapParallel(transform).filterNotNull()

/** Like [Iterable.map] but executes each [transform] invocation in a separate coroutine. */

suspend fun <A, B> Iterable<A>.mapParallel(transform: suspend (A) -> B): List<B> = coroutineScope {

    map { async(start = CoroutineStart.LAZY) { transform(it) } }.awaitAll()

}

/** Like [mapValues] but executes each [transform] invocation in a separate coroutine. */

suspend fun <K, A, B> Map<K, A>.mapValuesParallel(

    transform: suspend (Map.Entry<K, A>) -> B

): Map<K, B> = entries.mapParallel { it.key to transform(it) }.toMap()