package org.warp.cowdb.database;


import org.warp.cowdb.BlockInfo;
import org.warp.cowdb.IBlocksMetadata;

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;

public class DatabaseBlocksMetadata implements IBlocksMetadata {
	private final SeekableByteChannel metaFileChannel;
	private final int BLOCK_META_BYTES_COUNT = Long.BYTES + Integer.BYTES;
	private long firstFreeBlock;

	public DatabaseBlocksMetadata(Path metaFile) throws IOException {
		metaFileChannel = Files.newByteChannel(metaFile, StandardOpenOption.READ, StandardOpenOption.WRITE);
		firstFreeBlock = metaFileChannel.size() / BLOCK_META_BYTES_COUNT;
	}

	@Override
	public BlockInfo getBlockInfo(long blockId) throws IOException {
		if (blockId == EMPTY_BLOCK_ID) {
			return EMPTY_BLOCK_INFO;
		}
		ByteBuffer buffer = ByteBuffer.allocate(BLOCK_META_BYTES_COUNT);
		metaFileChannel.position(blockId * BLOCK_META_BYTES_COUNT).read(buffer);
		buffer.flip();
		long index = buffer.getLong();
		int size = buffer.getInt();
		return new BlockInfo(index, size);
	}

	@Override
	public long newBlock(long index, int size) throws IOException {
		long newBlockId = firstFreeBlock++;
		ByteBuffer data = ByteBuffer.allocate(BLOCK_META_BYTES_COUNT);
		data.putLong(index);
		data.putInt(size);
		data.flip();
		metaFileChannel.position(newBlockId * BLOCK_META_BYTES_COUNT).write(data);
		return newBlockId;
	}

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