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 java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import org.eclipse.jgit.internal.storage.pack.PackExt;
import org.eclipse.jgit.lib.BatchRefUpdate;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectIdRef;
import org.eclipse.jgit.lib.ProgressMonitor;
import org.eclipse.jgit.lib.Ref;
import org.eclipse.jgit.lib.Ref.Storage;
import org.eclipse.jgit.lib.RefDatabase;
import org.eclipse.jgit.revwalk.RevObject;
import org.eclipse.jgit.revwalk.RevTag;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.transport.ReceiveCommand;
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);
		}
	}

	static final AtomicInteger packId = new AtomicInteger();

	private final DfsObjDatabase objdb;
	private final RefDatabase refdb;
	private boolean performsAtomicTransactions = true;

	/**
	 * Initialize a new in-memory repository.
	 *
	 * @param repoDesc
	 *            description of the repository.
	 * @since 2.0
	 */
	public InMemoryRepository(DfsRepositoryDescription repoDesc) {
		this(new Builder().setRepositoryDescription(repoDesc));
	}

	InMemoryRepository(Builder builder) {
		super(builder);
		objdb = new MemObjDatabase(this);
		refdb = new MemRefDatabase();
	}

	@Override
	public DfsObjDatabase getObjectDatabase() {
		return objdb;
	}

	@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
	 */
	public void setPerformsAtomicTransactions(boolean atomic) {
		performsAtomicTransactions = atomic;
	}

	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 {
		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.
		}
	}

	/**
	 * A ref database storing all refs in-memory.
	 * <p>
	 * This class is protected (and not private) to facilitate testing using
	 * subclasses of InMemoryRepository.
	 */
    protected class MemRefDatabase extends DfsRefDatabase {
		private final ConcurrentMap<String, Ref> refs = new ConcurrentHashMap<String, Ref>();
		private final ReadWriteLock lock = new ReentrantReadWriteLock(true /* fair */);

		/**
		 * Initialize a new in-memory ref database.
		 */
		protected MemRefDatabase() {
			super(InMemoryRepository.this);
		}

		@Override
		public boolean performsAtomicTransactions() {
			return performsAtomicTransactions;
		}

		@Override
		public BatchRefUpdate newBatchUpdate() {
			return new BatchRefUpdate(this) {
				@Override
				public void execute(RevWalk walk, ProgressMonitor monitor)
						throws IOException {
					if (performsAtomicTransactions() && isAtomic()) {
						try {
							lock.writeLock().lock();
							batch(getCommands());
						} finally {
							lock.writeLock().unlock();
						}
					} else {
						super.execute(walk, monitor);
					}
				}
			};
		}

		@Override
		protected RefCache scanAllRefs() throws IOException {
			RefList.Builder<Ref> ids = new RefList.Builder<Ref>();
			RefList.Builder<Ref> sym = new RefList.Builder<Ref>();
			try {
				lock.readLock().lock();
				for (Ref ref : refs.values()) {
					if (ref.isSymbolic())
						sym.add(ref);
					ids.add(ref);
				}
			} finally {
				lock.readLock().unlock();
			}
			ids.sort();
			sym.sort();
			objdb.getCurrentPackList().markDirty();
			return new RefCache(ids.toRefList(), sym.toRefList());
		}

		private void batch(List<ReceiveCommand> cmds) {
			// Validate that the target exists in a new RevWalk, as the RevWalk
			// from the RefUpdate might be reading back unflushed objects.
			Map<ObjectId, ObjectId> peeled = new HashMap<>();
			try (RevWalk rw = new RevWalk(getRepository())) {
				for (ReceiveCommand c : cmds) {
					if (c.getResult() != ReceiveCommand.Result.NOT_ATTEMPTED) {
						ReceiveCommand.abort(cmds);
						return;
					}

					if (!ObjectId.zeroId().equals(c.getNewId())) {
						try {
							RevObject o = rw.parseAny(c.getNewId());
							if (o instanceof RevTag) {
								peeled.put(o, rw.peel(o).copy());
							}
						} catch (IOException e) {
							c.setResult(ReceiveCommand.Result.REJECTED_MISSING_OBJECT);
							ReceiveCommand.abort(cmds);
							return;
						}
					}
				}
			}

			// Check all references conform to expected old value.
			for (ReceiveCommand c : cmds) {
				Ref r = refs.get(c.getRefName());
				if (r == null) {
					if (c.getType() != ReceiveCommand.Type.CREATE) {
						c.setResult(ReceiveCommand.Result.LOCK_FAILURE);
						ReceiveCommand.abort(cmds);
						return;
					}
				} else {
					ObjectId objectId = r.getObjectId();
					if (r.isSymbolic() || objectId == null
							|| !objectId.equals(c.getOldId())) {
						c.setResult(ReceiveCommand.Result.LOCK_FAILURE);
						ReceiveCommand.abort(cmds);
						return;
					}
				}
			}

			// Write references.
			for (ReceiveCommand c : cmds) {
				if (c.getType() == ReceiveCommand.Type.DELETE) {
					refs.remove(c.getRefName());
					c.setResult(ReceiveCommand.Result.OK);
					continue;
				}

				ObjectId p = peeled.get(c.getNewId());
				Ref r;
				if (p != null) {
					r = new ObjectIdRef.PeeledTag(Storage.PACKED,
							c.getRefName(), c.getNewId(), p);
				} else {
					r = new ObjectIdRef.PeeledNonTag(Storage.PACKED,
							c.getRefName(), c.getNewId());
				}
				refs.put(r.getName(), r);
				c.setResult(ReceiveCommand.Result.OK);
			}
			clearCache();
		}

		@Override
		protected boolean compareAndPut(Ref oldRef, Ref newRef)
				throws IOException {
			try {
				lock.writeLock().lock();
				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;

				Ref cur = refs.get(name);
				if (cur != null) {
					if (eq(cur, oldRef))
						return refs.replace(name, cur, newRef);
				}

				if (oldRef.getStorage() == Storage.NEW)
					return refs.putIfAbsent(name, newRef) == null;

				return false;
			} finally {
				lock.writeLock().unlock();
			}
		}

		@Override
		protected boolean compareAndRemove(Ref oldRef) throws IOException {
			try {
				lock.writeLock().lock();
				String name = oldRef.getName();
				Ref cur = refs.get(name);
				if (cur != null && eq(cur, oldRef))
					return refs.remove(name, cur);
				else
					return false;
			} finally {
				lock.writeLock().unlock();
			}
		}

		private boolean eq(Ref a, Ref b) {
			if (!Objects.equals(a.getName(), b.getName()))
				return false;
			if (a.isSymbolic() != b.isSymbolic())
				return false;
			if (a.isSymbolic())
				return Objects.equals(a.getTarget().getName(), b.getTarget().getName());
			else
				return Objects.equals(a.getObjectId(), b.getObjectId());
		}
	}
}