strangedb/src/main/java/it/cavallium/strangedb/database/DatabaseBlocksMetadata.java

package it.cavallium.strangedb.database;


import it.cavallium.strangedb.BlockInfo;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousFileChannel;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;

public class DatabaseBlocksMetadata implements IBlocksMetadata {
	public static final BlockInfo ERROR_BLOCK_INFO = new BlockInfo(-2, 0);

	private final AsynchronousFileChannel metaFileChannel;
	private final int BLOCK_META_BYTES_COUNT = Long.BYTES + Integer.BYTES;
	private final DatabaseBlocksMetadataCache cache;
	private long firstFreeBlock;

	public DatabaseBlocksMetadata(Path metaFile) throws IOException {
		metaFileChannel = AsynchronousFileChannel.open(metaFile, StandardOpenOption.READ, StandardOpenOption.WRITE);
		firstFreeBlock = metaFileChannel.size() / BLOCK_META_BYTES_COUNT;
		this.cache = new DatabaseBlocksMetadataCache(this::writeBlockToDisk);
	}

	@Override
	public BlockInfo getBlockInfo(long blockId) throws IOException {
		if (blockId == EMPTY_BLOCK_ID) {
			return EMPTY_BLOCK_INFO;
		}
		BlockInfo blockInfo;
		if ((blockInfo = cache.get(blockId)) != ERROR_BLOCK_INFO) {
			return blockInfo;
		}
		ByteBuffer buffer = ByteBuffer.allocate(BLOCK_META_BYTES_COUNT);
		try {
			metaFileChannel.read(buffer, blockId * BLOCK_META_BYTES_COUNT).get();
		} catch (InterruptedException e) {
			throw new IOException(e);
		} catch (ExecutionException e) {
			throw new IOException(e.getCause());
		}
		buffer.flip();
		long index = buffer.getLong();
		int size = buffer.getInt();
		blockInfo = new BlockInfo(index, size);
		cache.put(blockId, blockInfo);
		return blockInfo;
	}

	@Override
	public long newBlock(long index, int size) throws IOException {
		if (size == 0) {
			return EMPTY_BLOCK_ID;
		}
		long newBlockId = firstFreeBlock++;
		BlockInfo blockInfo = new BlockInfo(index, size);
		cache.put(newBlockId, blockInfo);
		return newBlockId;
	}

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

	private Future<Integer> writeBlockToDisk(long blockId, long index, int size) {
		ByteBuffer data = ByteBuffer.allocate(BLOCK_META_BYTES_COUNT);
		data.putLong(index);
		data.putInt(size);
		data.flip();
		return metaFileChannel.write(data, blockId * BLOCK_META_BYTES_COUNT);
	}

	@Override
	public long getTotalBlocksCount() {
		return firstFreeBlock;
	}
}