/*
 * 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.
 */


package com.epam.dlab.backendapi.core.response.folderlistener;

import com.epam.dlab.backendapi.core.FileHandlerCallback;
import io.dropwizard.util.Duration;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.function.Supplier;

import static com.epam.dlab.backendapi.core.Constants.JSON_EXTENSION;
import static com.epam.dlab.backendapi.core.Constants.LOG_EXTENSION;

/* Handler for the file processing.
 */
public final class AsyncFileHandler implements Supplier<Boolean> {

	private static final Logger LOGGER = LoggerFactory.getLogger(AsyncFileHandler.class);

	/**
	 * File name.
	 */
	private final String fileName;
	/**
	 * Directory name.
	 */
	private final String directory;
	/**
	 * Implement of the file handler.
	 */
	private final FileHandlerCallback fileHandlerCallback;
	/**
	 * Timeout waiting for the file writing.
	 */
	private final Duration fileLengthCheckDelay;

	/**
	 * Create instance of the file handler.
	 *
	 * @param fileName             file name.
	 * @param directory            directory name.
	 * @param fileHandlerCallback  file handler for processing
	 * @param fileLengthCheckDelay timeout waiting for the file writing.
	 */
	public AsyncFileHandler(String fileName, String directory, FileHandlerCallback fileHandlerCallback,
							Duration fileLengthCheckDelay) {
		this.fileName = fileName;
		this.directory = directory;
		this.fileHandlerCallback = fileHandlerCallback;
		this.fileLengthCheckDelay = fileLengthCheckDelay;
	}

	@Override
	public Boolean get() {
		Path path = Paths.get(directory, fileName);
		try {
			boolean result = fileHandlerCallback.handle(fileName, readBytes(path));
			if (result) {
				try {
					Files.deleteIfExists(path);
					Files.deleteIfExists(getLogFile());
					LOGGER.trace("Response {} and log files has been deleted", path.toAbsolutePath());
				} catch (IOException e) {
					LOGGER.warn("Can't delete file {}", path.toAbsolutePath(), e);
				}
			}
			return result;
		} catch (Exception e) {
			LOGGER.error("Could not handle file {} async", path.toAbsolutePath(), e);
			fileHandlerCallback.handleError(e.getLocalizedMessage());
		}
		return false;
	}

	/**
	 * Returns the name of log file.
	 */
	private Path getLogFile() {
		return Paths.get(directory, fileName.replaceAll(JSON_EXTENSION, LOG_EXTENSION));
	}

	/**
	 * Returns the content of file.
	 *
	 * @param path source file.
	 * @return File content.
	 * @throws IOException
	 * @throws InterruptedException
	 */
	private byte[] readBytes(Path path) throws IOException, InterruptedException {
		File file = path.toFile();
		waitFileCompletelyWritten(file);
		return Files.readAllBytes(path);
	}

	/**
	 * Waiting for the file writing. This method is blocking and return control when
	 * the file will no longer resize.
	 *
	 * @param file source file.
	 */
	private void waitFileCompletelyWritten(File file) throws InterruptedException {
		long before;
		long after = file.length();
		do {
			before = after;
			Thread.sleep(fileLengthCheckDelay.toMilliseconds());
			after = file.length();
		} while (before != after);
	}
}