package util;

import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.file.Paths;
import java.util.Arrays;
import java.util.function.Consumer;
import lombok.NonNull;
import lombok.RequiredArgsConstructor;
import lombok.val;

/**
 * @author valekseev
 *
 * @since Oct 2, 2019
 */
@RequiredArgsConstructor
public class LockFileExecutionOperation<T> {

	private @NonNull final String lockFile;

	public void executeOnce(final @NonNull String checkValue, final @NonNull Consumer<T> operation, T object) throws IOException {
		try (val file = new RandomAccessFile(Paths.get(lockFile).toFile(), "rws")) {
			val lock = file.getChannel().lock();
			boolean executed = false;
			try {
				if (file.length() != 0) {
					lock.overlaps(0, file.length());
					val bb = ByteBuffer.allocate((int) file.length());
					lock.channel().read(bb, 0);
					executed = Arrays.equals(checkValue.getBytes(), bb.array());
				}
				if (!executed) {
					operation.accept(object);
					lock.channel().write(ByteBuffer.wrap(checkValue.getBytes()));
				}
			} finally {
				lock.release();
			}
		}
	}

}