/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 { PTransform, withName } from "./transform";
import { groupBy } from "./group_and_combine";
import { Root, PCollection } from "../pvalue";

/**
 * A Ptransform that represents a 'static' source with a list of elements passed at construction time. It
 * returns a PCollection that contains the elements in the input list.
 */
export function reshuffle<T>(): PTransform<PCollection<T>, PCollection<T>> {
  function reshuffle(input: PCollection<T>): PCollection<T> {
    return input
      .apply(
        withName(
          "groupByRandomKey",
          groupBy((x) => Math.random()),
        ),
      )
      .flatMap(withName("dropKeys", (kvs) => kvs.value));
  }

  return reshuffle;
}
