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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [https://neo4j.com]
 *
 * 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 org.neo4j.driver.internal.reactive;

import static org.neo4j.driver.internal.util.ErrorUtil.newResultConsumedError;
import static reactor.core.publisher.FluxSink.OverflowStrategy.IGNORE;

import java.util.List;
import java.util.concurrent.CompletionStage;
import java.util.function.BiConsumer;
import java.util.function.Supplier;
import org.neo4j.driver.Record;
import org.neo4j.driver.internal.cursor.RxResultCursor;
import org.neo4j.driver.internal.util.Futures;
import org.neo4j.driver.reactive.RxResult;
import org.neo4j.driver.summary.ResultSummary;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.FluxSink;
import reactor.core.publisher.Mono;

@Deprecated
@SuppressWarnings("DeprecatedIsStillUsed")
public class InternalRxResult implements RxResult {
    private Supplier> cursorFutureSupplier;
    private volatile CompletionStage cursorFuture;

    public InternalRxResult(Supplier> cursorFuture) {
        this.cursorFutureSupplier = cursorFuture;
    }

    @Override
    public Publisher> keys() {
        return Mono.defer(() -> Mono.fromCompletionStage(getCursorFuture())
                .map(RxResultCursor::keys)
                .onErrorMap(Futures::completionExceptionCause));
    }

    @Override
    public Publisher records() {
        return Flux.create(
                sink -> getCursorFuture().whenComplete((cursor, completionError) -> {
                    if (cursor != null) {
                        if (cursor.isDone()) {
                            sink.error(newResultConsumedError());
                        } else {
                            cursor.installRecordConsumer(createRecordConsumer(sink));
                            sink.onCancel(cursor::cancel);
                            sink.onRequest(cursor::request);
                        }
                    } else {
                        var error = Futures.completionExceptionCause(completionError);
                        sink.error(error);
                    }
                }),
                IGNORE);
    }

    /**
     * Defines how a subscriber shall consume records.
     * A record consumer holds a reference to a subscriber.
     * A publisher and/or a subscription who holds a reference to this consumer shall release the reference to this object
     * after subscription is done or cancelled so that the subscriber can be garbage collected.
     * @param sink the subscriber
     * @return a record consumer.
     */
    private BiConsumer createRecordConsumer(FluxSink sink) {
        return (r, e) -> {
            if (r != null) {
                sink.next(r);
            } else if (e != null) {
                sink.error(e);
            } else {
                sink.complete();
            }
        };
    }

    private CompletionStage getCursorFuture() {
        if (cursorFuture != null) {
            return cursorFuture;
        }
        return initCursorFuture();
    }

    synchronized CompletionStage initCursorFuture() {
        // A quick path to return
        if (cursorFuture != null) {
            return cursorFuture;
        }

        // now we obtained lock and we are going to be the one who assigns cursorFuture one and only once.
        cursorFuture = cursorFutureSupplier.get();
        cursorFutureSupplier = null; // we no longer need the reference to this object
        return this.cursorFuture;
    }

    @Override
    public Publisher consume() {
        return Mono.create(sink -> getCursorFuture().whenComplete((cursor, completionError) -> {
            if (cursor != null) {
                cursor.summaryAsync().whenComplete((summary, summaryCompletionError) -> {
                    var error = Futures.completionExceptionCause(summaryCompletionError);
                    if (summary != null) {
                        sink.success(summary);
                    } else {
                        sink.error(error);
                    }
                });
            } else {
                var error = Futures.completionExceptionCause(completionError);
                sink.error(error);
            }
        }));
    }

    @Override
    public Publisher isOpen() {
        return Mono.fromCompletionStage(getCursorFuture()).map(cursor -> !cursor.isDone());
    }

    // For testing purpose
    Supplier> cursorFutureSupplier() {
        return this.cursorFutureSupplier;
    }
}