package org.warp.jcwdb;

import com.esotericsoftware.kryo.io.Output;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.SeekableByteChannel;
import java.util.*;

public class FileAllocator implements AutoCloseable {
	private final SeekableByteChannel dataFileChannel;
	private volatile long allocableOffset;
	private volatile boolean closed;
	private final Object closeLock = new Object();
	private final Object allocateLock = new Object();
	
	public FileAllocator(SeekableByteChannel dataFileChannel) throws IOException {
		this.dataFileChannel = dataFileChannel;
		this.allocableOffset = this.dataFileChannel.size();
	}
	
	/**
	 * TODO: not implemented
	 * @param size
	 * @return offset
	 */
	public long allocate(int size) {
		checkClosed();
		synchronized (allocateLock) {
			long allocatedOffset = allocableOffset;
			allocableOffset += size;
			return allocatedOffset;
		}
	}

	
	public void close() throws IOException {
        if (closed) {
            return;
        }
        synchronized (closeLock) {
            if (closed) {
                return;
            }
            closed = true;
        }
	}
	
	/**
	 * Frees the unused bytes
	 * @param startPosition
	 * @param length
	 */
	public void markFree(long startPosition, int length) {
		checkClosed();
		// TODO: advanced feature, not implemented.
	}


	private void checkClosed() {
		if (closed) {
			throw new RuntimeException("Index Manager is closed.");
		}
	}
}