package org.warp.cowdb.database;

import org.warp.cowdb.IReferencesMetadata;
import org.warp.jcwdb.ann.DBClass;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SeekableByteChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;

import static org.warp.cowdb.IBlocksMetadata.EMPTY_BLOCK_ID;

public class DatabaseReferencesMetadata implements IReferencesMetadata {
	private final SeekableByteChannel metaFileChannel;
	private final int REF_META_BYTES_COUNT = Long.BYTES;
	private long firstFreeReference;

	public DatabaseReferencesMetadata(Path refMetaFile) throws IOException {
		metaFileChannel = Files.newByteChannel(refMetaFile, StandardOpenOption.READ, StandardOpenOption.WRITE);
		firstFreeReference = metaFileChannel.size() / REF_META_BYTES_COUNT;
	}

	@Override
	public long getReference(long reference) throws IOException {
		ByteBuffer buffer = ByteBuffer.allocate(REF_META_BYTES_COUNT);
		if (reference >= firstFreeReference) {
			return EMPTY_BLOCK_ID;
		}
		SeekableByteChannel currentFileChannel = metaFileChannel.position(reference * REF_META_BYTES_COUNT);
		currentFileChannel.read(buffer);
		buffer.flip();
		long block = buffer.getLong();
		if (buffer.limit() == 0 || block == 0xFFFFFFFFFFFFFFFFL) {
			return EMPTY_BLOCK_ID;
		}
		return block;
	}

	@Override
	public long newReference(long blockId) throws IOException {
		long newReference = firstFreeReference++;
		editReference(newReference, blockId);
		return newReference;
	}

	@Override
	public void editReference(long reference, long blockId) throws IOException {
		ByteBuffer data = ByteBuffer.allocate(REF_META_BYTES_COUNT);
		data.putLong(blockId);
		SeekableByteChannel currentFileChannel = metaFileChannel.position(reference * REF_META_BYTES_COUNT);
		data.flip();
		currentFileChannel.write(data);
	}

	@Override
	public void close() throws IOException {
		metaFileChannel.close();
	}

	@Override
	public long getFirstFreeReference() {
		return firstFreeReference;
	}
}