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Log4j2 Appender plugin pushing logs in batches to Elasticsearch (2.x/5.x/6.x/7.x/8.x) clusters
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package org.appenders.log4j2.elasticsearch.ahc;

/*-
 * #%L
 * log4j2-elasticsearch
 * %%
 * Copyright (C) 2022 Rafal Foltynski
 * %%
 * 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.
 * #L%
 */

import com.fasterxml.jackson.databind.ObjectReader;
import org.appenders.log4j2.elasticsearch.Deserializer;
import org.appenders.log4j2.elasticsearch.JacksonDeserializer;

import java.io.IOException;
import java.io.InputStream;
import java.util.concurrent.CountDownLatch;
import java.util.function.Function;

/**
 * Allows to execute blocking calls in asynchronous framework.
 * {@link #getResult()} will wait until the result is ready. Uses {@link java.util.concurrent.CountDownLatch} internally
 *
 * @param  response type
 */
public class BlockingResponseHandler implements ResponseHandler {

    protected final CountDownLatch countDownLatch = new CountDownLatch(1);
    protected final Deserializer deserializer;
    protected final Function fallbackResponseTemplate;
    protected T result;

    /**
     * @param objectReader used to deserialize response
     * @param fallbackResponseTemplate used to generate response in case of any failures
     */
    public BlockingResponseHandler(final ObjectReader objectReader, final Function fallbackResponseTemplate) {
        this.deserializer = new JacksonDeserializer<>(objectReader);
        this.fallbackResponseTemplate = fallbackResponseTemplate;
    }

    /**
     * @param deserializer used to deserialize response
     * @param fallbackResponseTemplate used to generate response in case of any failures
     */
    public BlockingResponseHandler(final Deserializer deserializer, final Function fallbackResponseTemplate) {
        this.deserializer = deserializer;
        this.fallbackResponseTemplate = fallbackResponseTemplate;
    }

    /**
     * Sets the result. Releases all threads waiting at {@link #getResult()}
     *
     * @param result result
     */
    @Override
    public final void completed(final T result) {
        this.result = result;
        countDownLatch.countDown();
    }

    /**
     * Handles exceptions. Sets response generated by {@link #fallbackResponseTemplate}.
     * Releases threads waiting at {@link #getResult()}
     *
     * @param exception exception to handle
     */
    @Override
    public final void failed(final Exception exception) {
        this.result = fallbackResponseTemplate.apply(exception);
        countDownLatch.countDown();
    }

    @Override
    public T deserializeResponse(final InputStream inputStream) throws IOException {
        if (inputStream == null) {
            return fallbackResponseTemplate.apply(null);
        }
        return deserializer.read(inputStream);
    }

    /**
     * @return result when available, waits otherwise
     */
    public T getResult() {
        try {
            countDownLatch.await();
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
        return result;
    }

}