package org.eclipse.jgit.internal.storage.dfs;
   
   import java.io.ByteArrayOutputStream;
   import java.io.FileNotFoundException;
   import java.io.IOException;
   import java.nio.ByteBuffer;
   import java.util.ArrayList;
   import java.util.Collection;
   import java.util.List;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.eclipse.jgit.annotations.Nullable;
  import org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource;
  import org.eclipse.jgit.internal.storage.pack.PackExt;
  import org.eclipse.jgit.internal.storage.reftable.ReftableConfig;
  import org.eclipse.jgit.lib.RefDatabase;
  
  /**
   * Git repository stored entirely in the local process memory.
   * <p>
   * This implementation builds on the DFS repository by storing all reference and
   * object data in the local process. It is not very efficient and exists only
   * for unit testing and small experiments.
   * <p>
   * The repository is thread-safe. Memory used is released only when this object
   * is garbage collected. Closing the repository has no impact on its memory.
   */
  public class InMemoryRepository extends DfsRepository {
  	/** Builder for in-memory repositories. */
  	public static class Builder
  			extends DfsRepositoryBuilder<Builder, InMemoryRepository> {
  		@Override
  		public InMemoryRepository build() throws IOException {
  			return new InMemoryRepository(this);
  		}
  	}
  
  	static final AtomicInteger packId = new AtomicInteger();
  
  	private final MemObjDatabase objdb;
  	private final MemRefDatabase refdb;
  	private String gitwebDescription;
  
  	/**
  	 * Initialize a new in-memory repository.
  	 *
  	 * @param repoDesc
  	 *            description of the repository.
  	 */
  	public InMemoryRepository(DfsRepositoryDescription repoDesc) {
  		this(new Builder().setRepositoryDescription(repoDesc));
  	}
  
  	InMemoryRepository(Builder builder) {
  		super(builder);
  		objdb = new MemObjDatabase(this);
  		refdb = new MemRefDatabase();
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public MemObjDatabase getObjectDatabase() {
  		return objdb;
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public RefDatabase getRefDatabase() {
  		return refdb;
  	}
  
  	/**
  	 * Enable (or disable) the atomic reference transaction support.
  	 * <p>
  	 * Useful for testing atomic support enabled or disabled.
  	 *
  	 * @param atomic
  	 *            whether to use atomic reference transaction support
  	 */
  	public void setPerformsAtomicTransactions(boolean atomic) {
  		refdb.performsAtomicTransactions = atomic;
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	@Nullable
  	public String getGitwebDescription() {
  		return gitwebDescription;
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public void setGitwebDescription(@Nullable String d) {
  		gitwebDescription = d;
  	}
  
  	/** DfsObjDatabase used by InMemoryRepository. */
  	public static class MemObjDatabase extends DfsObjDatabase {
  		private List<DfsPackDescription> packs = new ArrayList<>();
 		private int blockSize;
 
 		MemObjDatabase(DfsRepository repo) {
 			super(repo, new DfsReaderOptions());
 		}
 
 		/**
 		 * @param blockSize
 		 *            force a different block size for testing.
 		 */
 		public void setReadableChannelBlockSizeForTest(int blockSize) {
 			this.blockSize = blockSize;
 		}
 
 		@Override
 		protected synchronized List<DfsPackDescription> listPacks() {
 			return packs;
 		}
 
 		@Override
 		protected DfsPackDescription newPack(PackSource source) {
 			int id = packId.incrementAndGet();
 			return new MemPack(
 					"pack-" + id + "-" + source.name(), //$NON-NLS-1$ //$NON-NLS-2$
 					getRepository().getDescription(),
 					source);
 		}
 
 		@Override
 		protected synchronized void commitPackImpl(
 				Collection<DfsPackDescription> desc,
 				Collection<DfsPackDescription> replace) {
 			List<DfsPackDescription> n;
 			n = new ArrayList<>(desc.size() + packs.size());
 			n.addAll(desc);
 			n.addAll(packs);
 			if (replace != null)
 				n.removeAll(replace);
 			packs = n;
 			clearCache();
 		}
 
 		@Override
 		protected void rollbackPack(Collection<DfsPackDescription> desc) {
 			// Do nothing. Pack is not recorded until commitPack.
 		}
 
 		@Override
 		protected ReadableChannel openFile(DfsPackDescription desc, PackExt ext)
 				throws FileNotFoundException, IOException {
 			MemPack memPack = (MemPack) desc;
 			byte[] file = memPack.get(ext);
 			if (file == null)
 				throw new FileNotFoundException(desc.getFileName(ext));
 			return new ByteArrayReadableChannel(file, blockSize);
 		}
 
 		@Override
 		protected DfsOutputStream writeFile(DfsPackDescription desc,
 				PackExt ext) throws IOException {
 			MemPack memPack = (MemPack) desc;
 			return new Out() {
 				@Override
 				public void flush() {
 					memPack.put(ext, getData());
 				}
 			};
 		}
 
 		@Override
 		public long getApproximateObjectCount() {
 			long count = 0;
 			for (DfsPackDescription p : packs) {
 				count += p.getObjectCount();
 			}
 			return count;
 		}
 	}
 
 	private static class MemPack extends DfsPackDescription {
 		final byte[][] fileMap = new byte[PackExt.values().length][];
 
 		MemPack(String name, DfsRepositoryDescription repoDesc, PackSource source) {
 			super(repoDesc, name, source);
 		}
 
 		void put(PackExt ext, byte[] data) {
 			fileMap[ext.getPosition()] = data;
 		}
 
 		byte[] get(PackExt ext) {
 			return fileMap[ext.getPosition()];
 		}
 	}
 
 	private abstract static class Out extends DfsOutputStream {
 		private final ByteArrayOutputStream dst = new ByteArrayOutputStream();
 		private byte[] data;
 
 		@Override
 		public void write(byte[] buf, int off, int len) {
 			data = null;
 			dst.write(buf, off, len);
 		}
 
 		@Override
 		public int read(long position, ByteBuffer buf) {
 			byte[] d = getData();
 			int n = Math.min(buf.remaining(), d.length - (int) position);
 			if (n == 0)
 				return -1;
 			buf.put(d, (int) position, n);
 			return n;
 		}
 
 		byte[] getData() {
 			if (data == null)
 				data = dst.toByteArray();
 			return data;
 		}
 
 		@Override
 		public abstract void flush();
 
 		@Override
 		public void close() {
 			flush();
 		}
 	}
 
 	private static class ByteArrayReadableChannel implements ReadableChannel {
 		private final byte[] data;
 		private final int blockSize;
 		private int position;
 		private boolean open = true;
 
 		ByteArrayReadableChannel(byte[] buf, int blockSize) {
 			data = buf;
 			this.blockSize = blockSize;
 		}
 
 		@Override
 		public int read(ByteBuffer dst) {
 			int n = Math.min(dst.remaining(), data.length - position);
 			if (n == 0)
 				return -1;
 			dst.put(data, position, n);
 			position += n;
 			return n;
 		}
 
 		@Override
 		public void close() {
 			open = false;
 		}
 
 		@Override
 		public boolean isOpen() {
 			return open;
 		}
 
 		@Override
 		public long position() {
 			return position;
 		}
 
 		@Override
 		public void position(long newPosition) {
 			position = (int) newPosition;
 		}
 
 		@Override
 		public long size() {
 			return data.length;
 		}
 
 		@Override
 		public int blockSize() {
 			return blockSize;
 		}
 
 		@Override
 		public void setReadAheadBytes(int b) {
 			// Unnecessary on a byte array.
 		}
 	}
 
 	/** DfsRefDatabase used by InMemoryRepository. */
 	protected class MemRefDatabase extends DfsReftableDatabase {
 		boolean performsAtomicTransactions = true;
 
 		/** Initialize a new in-memory ref database. */
 		protected MemRefDatabase() {
 			super(InMemoryRepository.this);
 		}
 
 		@Override
 		public ReftableConfig getReftableConfig() {
 			ReftableConfig cfg = new ReftableConfig();
 			cfg.setAlignBlocks(false);
 			cfg.setIndexObjects(false);
 			cfg.fromConfig(getRepository().getConfig());
 			return cfg;
 		}
 
 		@Override
 		public boolean performsAtomicTransactions() {
 			return performsAtomicTransactions;
 		}
 	}
 }