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/*
 * Copyright (c) 2008-2024, Hazelcast, 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.
 */

package com.hazelcast.jet.impl.processor;

import com.hazelcast.function.FunctionEx;
import com.hazelcast.jet.Traverser;
import com.hazelcast.jet.aggregate.AggregateOperation;
import com.hazelcast.jet.aggregate.AggregateOperation1;
import com.hazelcast.jet.core.AbstractProcessor;
import com.hazelcast.jet.core.Processor;
import com.hazelcast.jet.impl.memory.AccumulationLimitExceededException;

import javax.annotation.Nonnull;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.function.BiFunction;
import java.util.function.Function;

import static com.hazelcast.internal.util.Preconditions.checkTrue;
import static java.util.Collections.singletonList;

/**
 * Batch processor that groups items by key and computes the supplied
 * aggregate operation on each group. The items may originate from one or
 * more inbound edges. The supplied aggregate operation must have as many
 * accumulation functions as there are inbound edges.
 */
public class GroupP extends AbstractProcessor {

    protected final Map keyToAcc = new HashMap<>();

    private final List> groupKeyFns;
    private final AggregateOperation aggrOp;
    private final BiFunction mapToOutputFn;

    private long maxEntries;
    private Traverser resultTraverser;

    public GroupP(
            @Nonnull List> groupKeyFns,
            @Nonnull AggregateOperation aggrOp,
            @Nonnull BiFunction mapToOutputFn
    ) {
        checkTrue(groupKeyFns.size() == aggrOp.arity(), groupKeyFns.size() + " key functions " +
                "provided for " + aggrOp.arity() + "-arity aggregate operation");
        this.groupKeyFns = groupKeyFns;
        this.aggrOp = aggrOp;
        this.mapToOutputFn = mapToOutputFn;
    }

    public  GroupP(
            @Nonnull FunctionEx groupKeyFn,
            @Nonnull AggregateOperation1 aggrOp,
            @Nonnull BiFunction mapToOutputFn
    ) {
        this(singletonList(groupKeyFn), aggrOp, mapToOutputFn);
    }

    @Override
    protected void init(@Nonnull Processor.Context context) throws Exception {
        maxEntries = context.maxProcessorAccumulatedRecords();
    }

    @Override
    @SuppressWarnings("unchecked")
    protected boolean tryProcess(int ordinal, @Nonnull Object item) {
        Function keyFn = (Function) groupKeyFns.get(ordinal);
        K key = keyFn.apply(item);
        A acc = keyToAcc.computeIfAbsent(key, k -> {
            if (keyToAcc.size() == maxEntries) {
                throw new AccumulationLimitExceededException();
            }

            return aggrOp.createFn().get();
        });
        aggrOp.accumulateFn(ordinal).accept(acc, item);
        return true;
    }

    @Override
    public boolean complete() {
        if (resultTraverser == null) {
            resultTraverser = new ResultTraverser()
                    // reuse null filtering done by map()
                    .map(e -> mapToOutputFn.apply(e.getKey(), aggrOp.finishFn().apply(e.getValue())));
        }
        return emitFromTraverser(resultTraverser);
    }

    @Override
    public boolean closeIsCooperative() {
        return true;
    }

    private class ResultTraverser implements Traverser> {
        private final Iterator> iter = keyToAcc.entrySet().iterator();

        @Override
        public Entry next() {
            if (!iter.hasNext()) {
                return null;
            }
            try {
                return iter.next();
            } finally {
                iter.remove();
            }
        }
    }
}