/*
    * Copyright (C) 2017, Google Inc. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.internal.storage.file;
  
  import static java.util.stream.Collectors.toList;
  import static org.eclipse.jgit.transport.ReceiveCommand.Result.LOCK_FAILURE;
  import static org.eclipse.jgit.transport.ReceiveCommand.Result.NOT_ATTEMPTED;
  import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_NONFASTFORWARD;
  import static org.eclipse.jgit.transport.ReceiveCommand.Result.REJECTED_OTHER_REASON;
  
  import java.io.IOException;
  import java.text.MessageFormat;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  
  import org.eclipse.jgit.annotations.Nullable;
  import org.eclipse.jgit.errors.LockFailedException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.internal.storage.file.RefDirectory.PackedRefList;
  import org.eclipse.jgit.lib.BatchRefUpdate;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectIdRef;
  import org.eclipse.jgit.lib.PersonIdent;
  import org.eclipse.jgit.lib.ProgressMonitor;
  import org.eclipse.jgit.lib.Ref;
  import org.eclipse.jgit.lib.RefDatabase;
  import org.eclipse.jgit.lib.ReflogEntry;
  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;
  
  /**
   * Implementation of {@link BatchRefUpdate} that uses the {@code packed-refs}
   * file to support atomically updating multiple refs.
   * <p>
   * The algorithm is designed to be compatible with traditional single ref
   * updates operating on single refs only. Regardless of success or failure, the
   * results are atomic: from the perspective of any reader, either all updates in
   * the batch will be visible, or none will. In the case of process failure
   * during any of the following steps, removal of stale lock files is always
   * safe, and will never result in an inconsistent state, although the update may
   * or may not have been applied.
   * <p>
   * The algorithm is:
   * <ol>
   * <li>Pack loose refs involved in the transaction using the normal pack-refs
   * operation. This ensures that creating lock files in the following step
   * succeeds even if a batch contains both a delete of {@code refs/x} (loose) and
   * a create of {@code refs/x/y}.</li>
   * <li>Create locks for all loose refs involved in the transaction, even if they
   * are not currently loose.</li>
   * <li>Pack loose refs again, this time while holding all lock files (see {@link
   * RefDirectory#pack(Map)}), without deleting them afterwards. This covers a
   * potential race where new loose refs were created after the initial packing
   * step. If no new loose refs were created during this race, this step does not
   * modify any files on disk. Keep the merged state in memory.</li>
   * <li>Update the in-memory packed refs with the commands in the batch, possibly
   * failing the whole batch if any old ref values do not match.</li>
   * <li>If the update succeeds, lock {@code packed-refs} and commit by atomically
   * renaming the lock file.</li>
   * <li>Delete loose ref lock files.</li>
   * </ol>
   *
   * Because the packed-refs file format is a sorted list, this algorithm is
   * linear in the total number of refs, regardless of the batch size. This can be
   * a significant slowdown on repositories with large numbers of refs; callers
   * that prefer speed over atomicity should use {@code setAtomic(false)}. As an
   * optimization, an update containing a single ref update does not use the
   * packed-refs protocol.
   */
  class PackedBatchRefUpdate extends BatchRefUpdate {
  	private RefDirectory refdb;
  
  	PackedBatchRefUpdate(RefDirectory refdb) {
  		super(refdb);
  		this.refdb = refdb;
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public void execute(RevWalk walk, ProgressMonitor monitor,
  			List<String> options) throws IOException {
  		if (!isAtomic()) {
 			// Use default one-by-one implementation.
 			super.execute(walk, monitor, options);
 			return;
 		}
 		List<ReceiveCommand> pending =
 				ReceiveCommand.filter(getCommands(), NOT_ATTEMPTED);
 		if (pending.isEmpty()) {
 			return;
 		}
 		if (pending.size() == 1) {
 			// Single-ref updates are always atomic, no need for packed-refs.
 			super.execute(walk, monitor, options);
 			return;
 		}
 		if (containsSymrefs(pending)) {
 			// packed-refs file cannot store symrefs
 			reject(pending.get(0), REJECTED_OTHER_REASON,
 					JGitText.get().atomicSymRefNotSupported, pending);
 			return;
 		}
 
 		// Required implementation details copied from super.execute.
 		if (!blockUntilTimestamps(MAX_WAIT)) {
 			return;
 		}
 		if (options != null) {
 			setPushOptions(options);
 		}
 		// End required implementation details.
 
 		// Check for conflicting names before attempting to acquire locks, since
 		// lockfile creation may fail on file/directory conflicts.
 		if (!checkConflictingNames(pending)) {
 			return;
 		}
 
 		if (!checkObjectExistence(walk, pending)) {
 			return;
 		}
 
 		if (!checkNonFastForwards(walk, pending)) {
 			return;
 		}
 
 		// Pack refs normally, so we can create lock files even in the case where
 		// refs/x is deleted and refs/x/y is created in this batch.
 		try {
 			refdb.pack(
 					pending.stream().map(ReceiveCommand::getRefName).collect(toList()));
 		} catch (LockFailedException e) {
 			lockFailure(pending.get(0), pending);
 			return;
 		}
 
 		Map<String, LockFile> locks = null;
 		refdb.inProcessPackedRefsLock.lock();
 		try {
 			PackedRefList oldPackedList;
 			if (!refdb.isInClone()) {
 				locks = lockLooseRefs(pending);
 				if (locks == null) {
 					return;
 				}
 				oldPackedList = refdb.pack(locks);
 			} else {
 				// During clone locking isn't needed since no refs exist yet.
 				// This also helps to avoid problems with refs only differing in
 				// case on a case insensitive filesystem (bug 528497)
 				oldPackedList = refdb.getPackedRefs();
 			}
 			RefList<Ref> newRefs = applyUpdates(walk, oldPackedList, pending);
 			if (newRefs == null) {
 				return;
 			}
 			LockFile packedRefsLock = refdb.lockPackedRefs();
 			if (packedRefsLock == null) {
 				lockFailure(pending.get(0), pending);
 				return;
 			}
 			// commitPackedRefs removes lock file (by renaming over real file).
 			refdb.commitPackedRefs(packedRefsLock, newRefs, oldPackedList,
 					true);
 		} finally {
 			try {
 				unlockAll(locks);
 			} finally {
 				refdb.inProcessPackedRefsLock.unlock();
 			}
 		}
 
 		refdb.fireRefsChanged();
 		pending.forEach(c -> c.setResult(ReceiveCommand.Result.OK));
 		writeReflog(pending);
 	}
 
 	private static boolean containsSymrefs(List<ReceiveCommand> commands) {
 		for (ReceiveCommand cmd : commands) {
 			if (cmd.getOldSymref() != null || cmd.getNewSymref() != null) {
 				return true;
 			}
 		}
 		return false;
 	}
 
 	private boolean checkConflictingNames(List<ReceiveCommand> commands)
 			throws IOException {
 		Set<String> takenNames = new HashSet<>();
 		Set<String> takenPrefixes = new HashSet<>();
 		Set<String> deletes = new HashSet<>();
 		for (ReceiveCommand cmd : commands) {
 			if (cmd.getType() != ReceiveCommand.Type.DELETE) {
 				takenNames.add(cmd.getRefName());
 				addPrefixesTo(cmd.getRefName(), takenPrefixes);
 			} else {
 				deletes.add(cmd.getRefName());
 			}
 		}
 		Set<String> initialRefs = refdb.getRefs(RefDatabase.ALL).keySet();
 		for (String name : initialRefs) {
 			if (!deletes.contains(name)) {
 				takenNames.add(name);
 				addPrefixesTo(name, takenPrefixes);
 			}
 		}
 
 		for (ReceiveCommand cmd : commands) {
 			if (cmd.getType() != ReceiveCommand.Type.DELETE &&
 					takenPrefixes.contains(cmd.getRefName())) {
 				// This ref is a prefix of some other ref. This check doesn't apply when
 				// this command is a delete, because if the ref is deleted nobody will
 				// ever be creating a loose ref with that name.
 				lockFailure(cmd, commands);
 				return false;
 			}
 			for (String prefix : getPrefixes(cmd.getRefName())) {
 				if (takenNames.contains(prefix)) {
 					// A prefix of this ref is already a refname. This check does apply
 					// when this command is a delete, because we would need to create the
 					// refname as a directory in order to create a lockfile for the
 					// to-be-deleted ref.
 					lockFailure(cmd, commands);
 					return false;
 				}
 			}
 		}
 		return true;
 	}
 
 	private boolean checkObjectExistence(RevWalk walk,
 			List<ReceiveCommand> commands) throws IOException {
 		for (ReceiveCommand cmd : commands) {
 			try {
 				if (!cmd.getNewId().equals(ObjectId.zeroId())) {
 					walk.parseAny(cmd.getNewId());
 				}
 			} catch (MissingObjectException e) {
 				// ReceiveCommand#setResult(Result) converts REJECTED to
 				// REJECTED_NONFASTFORWARD, even though that result is also used for a
 				// missing object. Eagerly handle this case so we can set the right
 				// result.
 				reject(cmd, ReceiveCommand.Result.REJECTED_MISSING_OBJECT, commands);
 				return false;
 			}
 		}
 		return true;
 	}
 
 	private boolean checkNonFastForwards(RevWalk walk,
 			List<ReceiveCommand> commands) throws IOException {
 		if (isAllowNonFastForwards()) {
 			return true;
 		}
 		for (ReceiveCommand cmd : commands) {
 			cmd.updateType(walk);
 			if (cmd.getType() == ReceiveCommand.Type.UPDATE_NONFASTFORWARD) {
 				reject(cmd, REJECTED_NONFASTFORWARD, commands);
 				return false;
 			}
 		}
 		return true;
 	}
 
 	/**
 	 * Lock loose refs corresponding to a list of commands.
 	 *
 	 * @param commands
 	 *            commands that we intend to execute.
 	 * @return map of ref name in the input commands to lock file. Always contains
 	 *         one entry for each ref in the input list. All locks are acquired
 	 *         before returning. If any lock was not able to be acquired: the
 	 *         return value is null; no locks are held; and all commands that were
 	 *         pending are set to fail with {@code LOCK_FAILURE}.
 	 * @throws IOException
 	 *             an error occurred other than a failure to acquire; no locks are
 	 *             held if this exception is thrown.
 	 */
 	@Nullable
 	private Map<String, LockFile> lockLooseRefs(List<ReceiveCommand> commands)
 			throws IOException {
 		ReceiveCommand failed = null;
 		Map<String, LockFile> locks = new HashMap<>();
 		try {
 			RETRY: for (int ms : refdb.getRetrySleepMs()) {
 				failed = null;
 				// Release all locks before trying again, to prevent deadlock.
 				unlockAll(locks);
 				locks.clear();
 				RefDirectory.sleep(ms);
 
 				for (ReceiveCommand c : commands) {
 					String name = c.getRefName();
 					LockFile lock = new LockFile(refdb.fileFor(name));
 					if (locks.put(name, lock) != null) {
 						throw new IOException(
 								MessageFormat.format(JGitText.get().duplicateRef, name));
 					}
 					if (!lock.lock()) {
 						failed = c;
 						continue RETRY;
 					}
 				}
 				Map<String, LockFile> result = locks;
 				locks = null;
 				return result;
 			}
 		} finally {
 			unlockAll(locks);
 		}
 		lockFailure(failed != null ? failed : commands.get(0), commands);
 		return null;
 	}
 
 	private static RefList<Ref> applyUpdates(RevWalk walk, RefList<Ref> refs,
 			List<ReceiveCommand> commands) throws IOException {
 		// Construct a new RefList by merging the old list with the updates.
 		// This assumes that each ref occurs at most once as a ReceiveCommand.
 		Collections.sort(commands,
 				Comparator.comparing(ReceiveCommand::getRefName));
 
 		int delta = 0;
 		for (ReceiveCommand c : commands) {
 			switch (c.getType()) {
 			case DELETE:
 				delta--;
 				break;
 			case CREATE:
 				delta++;
 				break;
 			default:
 			}
 		}
 
 		RefList.Builder<Ref> b = new RefList.Builder<>(refs.size() + delta);
 		int refIdx = 0;
 		int cmdIdx = 0;
 		while (refIdx < refs.size() || cmdIdx < commands.size()) {
 			Ref ref = (refIdx < refs.size()) ? refs.get(refIdx) : null;
 			ReceiveCommand cmd = (cmdIdx < commands.size())
 					? commands.get(cmdIdx)
 					: null;
 			int cmp = 0;
 			if (ref != null && cmd != null) {
 				cmp = ref.getName().compareTo(cmd.getRefName());
 			} else if (ref == null) {
 				cmp = 1;
 			} else if (cmd == null) {
 				cmp = -1;
 			}
 
 			if (cmp < 0) {
 				b.add(ref);
 				refIdx++;
 			} else if (cmp > 0) {
 				assert cmd != null;
 				if (cmd.getType() != ReceiveCommand.Type.CREATE) {
 					lockFailure(cmd, commands);
 					return null;
 				}
 
 				b.add(peeledRef(walk, cmd));
 				cmdIdx++;
 			} else {
 				assert cmd != null;
 				assert ref != null;
 				if (!cmd.getOldId().equals(ref.getObjectId())) {
 					lockFailure(cmd, commands);
 					return null;
 				}
 
 				if (cmd.getType() != ReceiveCommand.Type.DELETE) {
 					b.add(peeledRef(walk, cmd));
 				}
 				cmdIdx++;
 				refIdx++;
 			}
 		}
 		return b.toRefList();
 	}
 
 	private void writeReflog(List<ReceiveCommand> commands) {
 		PersonIdent ident = getRefLogIdent();
 		if (ident == null) {
 			ident = new PersonIdent(refdb.getRepository());
 		}
 		for (ReceiveCommand cmd : commands) {
 			// Assume any pending commands have already been executed atomically.
 			if (cmd.getResult() != ReceiveCommand.Result.OK) {
 				continue;
 			}
 			String name = cmd.getRefName();
 
 			if (cmd.getType() == ReceiveCommand.Type.DELETE) {
 				try {
 					RefDirectory.delete(refdb.logFor(name), RefDirectory.levelsIn(name));
 				} catch (IOException e) {
 					// Ignore failures, see below.
 				}
 				continue;
 			}
 
 			if (isRefLogDisabled(cmd)) {
 				continue;
 			}
 
 			String msg = getRefLogMessage(cmd);
 			if (isRefLogIncludingResult(cmd)) {
 				String strResult = toResultString(cmd);
 				if (strResult != null) {
 					msg = msg.isEmpty()
 							? strResult : msg + ": " + strResult; //$NON-NLS-1$
 				}
 			}
 			try {
 				new ReflogWriter(refdb, isForceRefLog(cmd))
 						.log(name, cmd.getOldId(), cmd.getNewId(), ident, msg);
 			} catch (IOException e) {
 				// Ignore failures, but continue attempting to write more reflogs.
 				//
 				// In this storage format, it is impossible to atomically write the
 				// reflog with the ref updates, so we have to choose between:
 				// a. Propagating this exception and claiming failure, even though the
 				//    actual ref updates succeeded.
 				// b. Ignoring failures writing the reflog, so we claim success if and
 				//    only if the ref updates succeeded.
 				// We choose (b) in order to surprise callers the least.
 				//
 				// Possible future improvements:
 				// * Log a warning to a logger.
 				// * Retry a fixed number of times in case the error was transient.
 			}
 		}
 	}
 
 	private String toResultString(ReceiveCommand cmd) {
 		switch (cmd.getType()) {
 		case CREATE:
 			return ReflogEntry.PREFIX_CREATED;
 		case UPDATE:
 			// Match the behavior of a single RefUpdate. In that case, setting the
 			// force bit completely bypasses the potentially expensive isMergedInto
 			// check, by design, so the reflog message may be inaccurate.
 			//
 			// Similarly, this class bypasses the isMergedInto checks when the force
 			// bit is set, meaning we can't actually distinguish between UPDATE and
 			// UPDATE_NONFASTFORWARD when isAllowNonFastForwards() returns true.
 			return isAllowNonFastForwards()
 					? ReflogEntry.PREFIX_FORCED_UPDATE : ReflogEntry.PREFIX_FAST_FORWARD;
 		case UPDATE_NONFASTFORWARD:
 			return ReflogEntry.PREFIX_FORCED_UPDATE;
 		default:
 			return null;
 		}
 	}
 
 	private static Ref peeledRef(RevWalk walk, ReceiveCommand cmd)
 			throws IOException {
 		ObjectId newId = cmd.getNewId().copy();
 		RevObject obj = walk.parseAny(newId);
 		if (obj instanceof RevTag) {
 			return new ObjectIdRef.PeeledTag(
 					Ref.Storage.PACKED, cmd.getRefName(), newId, walk.peel(obj).copy());
 		}
 		return new ObjectIdRef.PeeledNonTag(
 				Ref.Storage.PACKED, cmd.getRefName(), newId);
 	}
 
 	private static void unlockAll(@Nullable Map<?, LockFile> locks) {
 		if (locks != null) {
 			locks.values().forEach(LockFile::unlock);
 		}
 	}
 
 	private static void lockFailure(ReceiveCommand cmd,
 			List<ReceiveCommand> commands) {
 		reject(cmd, LOCK_FAILURE, commands);
 	}
 
 	private static void reject(ReceiveCommand cmd, ReceiveCommand.Result result,
 			List<ReceiveCommand> commands) {
 		reject(cmd, result, null, commands);
 	}
 
 	private static void reject(ReceiveCommand cmd, ReceiveCommand.Result result,
 			String why, List<ReceiveCommand> commands) {
 		cmd.setResult(result, why);
 		for (ReceiveCommand c2 : commands) {
 			if (c2.getResult() == ReceiveCommand.Result.OK) {
 				// Undo OK status so ReceiveCommand#abort aborts it. Assumes this method
 				// is always called before committing any updates to disk.
 				c2.setResult(ReceiveCommand.Result.NOT_ATTEMPTED);
 			}
 		}
 		ReceiveCommand.abort(commands);
 	}
 }