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.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Objects;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.eclipse.jgit.internal.storage.pack.PackExt;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectIdRef;
  import org.eclipse.jgit.lib.Ref;
  import org.eclipse.jgit.lib.Ref.Storage;
  import org.eclipse.jgit.lib.SymbolicRef;
  import org.eclipse.jgit.revwalk.RevWalk;
  import org.eclipse.jgit.util.RefList;
  
  /**
   * 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);
  		}
  	}
  
  	private static final AtomicInteger packId = new AtomicInteger();
  
  	private final DfsObjDatabase objdb;
  
  	private final DfsRefDatabase refdb;
  
  	/**
  	 * Initialize a new in-memory repository.
  	 *
  	 * @param repoDesc
  	 *            description of the repository.
  	 * @since 2.0
  	 */
  	public InMemoryRepository(DfsRepositoryDescription repoDesc) {
  		this(new Builder().setRepositoryDescription(repoDesc));
  	}
  
  	private InMemoryRepository(Builder builder) {
  		super(builder);
  		objdb = new MemObjDatabase(this);
  		refdb = new MemRefDatabase();
  	}
  
  	@Override
  	public DfsObjDatabase getObjectDatabase() {
  		return objdb;
  	}
  
  	@Override
  	public DfsRefDatabase getRefDatabase() {
  		return refdb;
  	}
  
  	private class MemObjDatabase extends DfsObjDatabase {
  		private List<DfsPackDescription> packs = new ArrayList<DfsPackDescription>();
  
  		MemObjDatabase(DfsRepository repo) {
  			super(repo, new DfsReaderOptions());
  		}
  
  		@Override
  		protected synchronized List<DfsPackDescription> listPacks() {
  			return packs;
  		}
  
  		@Override
  		protected DfsPackDescription newPack(PackSource source) {
  			int id = packId.incrementAndGet();
  			DfsPackDescription desc = new MemPack(
  					"pack-" + id + "-" + source.name(), //$NON-NLS-1$ //$NON-NLS-2$
  					getRepository().getDescription());
  			return desc.setPackSource(source);
  		}
  
 		@Override
 		protected synchronized void commitPackImpl(
 				Collection<DfsPackDescription> desc,
 				Collection<DfsPackDescription> replace) {
 			List<DfsPackDescription> n;
 			n = new ArrayList<DfsPackDescription>(desc.size() + packs.size());
 			n.addAll(desc);
 			n.addAll(packs);
 			if (replace != null)
 				n.removeAll(replace);
 			packs = n;
 		}
 
 		@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.fileMap.get(ext);
 			if (file == null)
 				throw new FileNotFoundException(desc.getFileName(ext));
 			return new ByteArrayReadableChannel(file);
 		}
 
 		@Override
 		protected DfsOutputStream writeFile(
 				DfsPackDescription desc, final PackExt ext) throws IOException {
 			final MemPack memPack = (MemPack) desc;
 			return new Out() {
 				@Override
 				public void flush() {
 					memPack.fileMap.put(ext, getData());
 				}
 			};
 		}
 	}
 
 	private static class MemPack extends DfsPackDescription {
 		private final Map<PackExt, byte[]>
 				fileMap = new HashMap<PackExt, byte[]>();
 
 		MemPack(String name, DfsRepositoryDescription repoDesc) {
 			super(repoDesc, name);
 		}
 	}
 
 	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 int position;
 
 		private boolean open = true;
 
 		ByteArrayReadableChannel(byte[] buf) {
 			data = buf;
 		}
 
 		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;
 		}
 
 		public void close() {
 			open = false;
 		}
 
 		public boolean isOpen() {
 			return open;
 		}
 
 		public long position() {
 			return position;
 		}
 
 		public void position(long newPosition) {
 			position = (int) newPosition;
 		}
 
 		public long size() {
 			return data.length;
 		}
 
 		public int blockSize() {
 			return 0;
 		}
 
 		public void setReadAheadBytes(int b) {
 			// Unnecessary on a byte array.
 		}
 	}
 
 	private class MemRefDatabase extends DfsRefDatabase {
 		private final ConcurrentMap<String, Ref> refs = new ConcurrentHashMap<String, Ref>();
 
 		MemRefDatabase() {
 			super(InMemoryRepository.this);
 		}
 
 		@Override
 		protected RefCache scanAllRefs() throws IOException {
 			RefList.Builder<Ref> ids = new RefList.Builder<Ref>();
 			RefList.Builder<Ref> sym = new RefList.Builder<Ref>();
 			for (Ref ref : refs.values()) {
 				if (ref.isSymbolic())
 					sym.add(ref);
 				ids.add(ref);
 			}
 			ids.sort();
 			sym.sort();
 			return new RefCache(ids.toRefList(), sym.toRefList());
 		}
 
 		@Override
 		protected boolean compareAndPut(Ref oldRef, Ref newRef)
 				throws IOException {
 			ObjectId id = newRef.getObjectId();
 			if (id != null) {
 				try (RevWalk rw = new RevWalk(getRepository())) {
 					// Validate that the target exists in a new RevWalk, as the RevWalk
 					// from the RefUpdate might be reading back unflushed objects.
 					rw.parseAny(id);
 				}
 			}
 			String name = newRef.getName();
 			if (oldRef == null)
 				return refs.putIfAbsent(name, newRef) == null;
 
 			synchronized (refs) {
 				Ref cur = refs.get(name);
 				Ref toCompare = cur;
 				if (toCompare != null) {
 					if (toCompare.isSymbolic()) {
 						// Arm's-length dereference symrefs before the compare, since
 						// DfsRefUpdate#doLink(String) stores them undereferenced.
 						Ref leaf = toCompare.getLeaf();
 						if (leaf.getObjectId() == null) {
 							leaf = refs.get(leaf.getName());
 							if (leaf.isSymbolic())
 								// Not supported at the moment.
 								throw new IllegalArgumentException();
 							toCompare = new SymbolicRef(
 									name,
 									new ObjectIdRef.Unpeeled(
 											Storage.NEW,
 											leaf.getName(),
 											leaf.getObjectId()));
 						} else
 							toCompare = toCompare.getLeaf();
 					}
 					if (eq(toCompare, oldRef))
 						return refs.replace(name, cur, newRef);
 				}
 			}
 
 			if (oldRef.getStorage() == Storage.NEW)
 				return refs.putIfAbsent(name, newRef) == null;
 
 			return false;
 		}
 
 		@Override
 		protected boolean compareAndRemove(Ref oldRef) throws IOException {
 			String name = oldRef.getName();
 			Ref cur = refs.get(name);
 			if (cur != null && eq(cur, oldRef))
 				return refs.remove(name, cur);
 			else
 				return false;
 		}
 
 		private boolean eq(Ref a, Ref b) {
 			if (!Objects.equals(a.getName(), b.getName()))
 				return false;
 			// Compare leaf object IDs, since the oldRef passed into compareAndPut
 			// when detaching a symref is an ObjectIdRef.
 			return Objects.equals(a.getLeaf().getObjectId(),
 					b.getLeaf().getObjectId());
 		}
 	}
 }