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    * and other copyright owners as documented in the project's IP log.
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    * This program and the accompanying materials are made available
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    * accompanies this distribution, is reproduced below, and is
    * available at http://www.eclipse.org/org/documents/edl-v10.php
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  package org.eclipse.jgit.internal.ketch;
  
  import static org.eclipse.jgit.internal.ketch.Proposal.State.RUNNING;
  
  import java.io.IOException;
  import java.time.Duration;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.TimeoutException;
  import java.util.stream.Collectors;
  
  import org.eclipse.jgit.annotations.Nullable;
  import org.eclipse.jgit.internal.storage.reftree.Command;
  import org.eclipse.jgit.internal.storage.reftree.RefTree;
  import org.eclipse.jgit.lib.CommitBuilder;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectInserter;
  import org.eclipse.jgit.lib.PersonIdent;
  import org.eclipse.jgit.lib.Ref;
  import org.eclipse.jgit.lib.Repository;
  import org.eclipse.jgit.revwalk.RevCommit;
  import org.eclipse.jgit.revwalk.RevWalk;
  import org.eclipse.jgit.transport.ReceiveCommand;
  import org.eclipse.jgit.util.time.ProposedTimestamp;
  
  /** A {@link Round} that aggregates and sends user {@link Proposal}s. */
  class ProposalRound extends Round {
  	private final List<Proposal> todo;
  	private RefTree queuedTree;
  
  	ProposalRound(KetchLeader leader, LogIndex head, List<Proposal> todo,
  			@Nullable RefTree tree) {
  		super(leader, head);
  		this.todo = todo;
  
  		if (tree != null && canCombine(todo)) {
  			this.queuedTree = tree;
  		} else {
  			leader.roundHoldsReferenceToRefTree = false;
  		}
  	}
  
  	private static boolean canCombine(List<Proposal> todo) {
  		Proposal first = todo.get(0);
  		for (int i = 1; i < todo.size(); i++) {
  			if (!canCombine(first, todo.get(i))) {
  				return false;
  			}
  		}
  		return true;
  	}
 
 	private static boolean canCombine(Proposal a, Proposal b) {
 		String aMsg = nullToEmpty(a.getMessage());
 		String bMsg = nullToEmpty(b.getMessage());
 		return aMsg.equals(bMsg) && canCombine(a.getAuthor(), b.getAuthor());
 	}
 
 	private static String nullToEmpty(@Nullable String str) {
 		return str != null ? str : ""; //$NON-NLS-1$
 	}
 
 	private static boolean canCombine(@Nullable PersonIdent a,
 			@Nullable PersonIdent b) {
 		if (a != null && b != null) {
 			// Same name and email address. Combine timestamp as the two
 			// proposals are running concurrently and appear together or
 			// not at all from the point of view of an outside reader.
 			return a.getName().equals(b.getName())
 					&& a.getEmailAddress().equals(b.getEmailAddress());
 		}
 
 		// If a and b are null, both will be the system identity.
 		return a == null && b == null;
 	}
 
 	@Override
 	void start() throws IOException {
 		for (Proposal p : todo) {
 			p.notifyState(RUNNING);
 		}
 		try {
 			ObjectId id;
 			try (Repository git = leader.openRepository();
 					ProposedTimestamp ts = getSystem().getClock().propose()) {
 				id = insertProposals(git, ts);
 				blockUntil(ts);
 			}
 			runAsync(id);
 		} catch (NoOp e) {
 			for (Proposal p : todo) {
 				p.success();
 			}
 			leader.lock.lock();
 			try {
 				leader.nextRound();
 			} finally {
 				leader.lock.unlock();
 			}
 		} catch (IOException e) {
 			abort();
 			throw e;
 		}
 	}
 
 	private ObjectId insertProposals(Repository git, ProposedTimestamp ts)
 			throws IOException, NoOp {
 		ObjectId id;
 		try (ObjectInserter inserter = git.newObjectInserter()) {
 			// TODO(sop) Process signed push certificates.
 
 			if (queuedTree != null) {
 				id = insertSingleProposal(git, ts, inserter);
 			} else {
 				id = insertMultiProposal(git, ts, inserter);
 			}
 
 			stageCommands = makeStageList(git, inserter);
 			inserter.flush();
 		}
 		return id;
 	}
 
 	private ObjectId insertSingleProposal(Repository git, ProposedTimestamp ts,
 			ObjectInserter inserter) throws IOException, NoOp {
 		// Fast path: tree is passed in with all proposals applied.
 		ObjectId treeId = queuedTree.writeTree(inserter);
 		queuedTree = null;
 		leader.roundHoldsReferenceToRefTree = false;
 
 		if (!ObjectId.zeroId().equals(acceptedOldIndex)) {
 			try (RevWalk rw = new RevWalk(git)) {
 				RevCommit c = rw.parseCommit(acceptedOldIndex);
 				if (treeId.equals(c.getTree())) {
 					throw new NoOp();
 				}
 			}
 		}
 
 		Proposal p = todo.get(0);
 		CommitBuilder b = new CommitBuilder();
 		b.setTreeId(treeId);
 		if (!ObjectId.zeroId().equals(acceptedOldIndex)) {
 			b.setParentId(acceptedOldIndex);
 		}
 		b.setCommitter(leader.getSystem().newCommitter(ts));
 		b.setAuthor(p.getAuthor() != null ? p.getAuthor() : b.getCommitter());
 		b.setMessage(message(p));
 		return inserter.insert(b);
 	}
 
 	private ObjectId insertMultiProposal(Repository git, ProposedTimestamp ts,
 			ObjectInserter inserter) throws IOException, NoOp {
 		// The tree was not passed in, or there are multiple proposals
 		// each needing their own commit. Reset the tree and replay each
 		// proposal in order as individual commits.
 		ObjectId lastIndex = acceptedOldIndex;
 		ObjectId oldTreeId;
 		RefTree tree;
 		if (ObjectId.zeroId().equals(lastIndex)) {
 			oldTreeId = ObjectId.zeroId();
 			tree = RefTree.newEmptyTree();
 		} else {
 			try (RevWalk rw = new RevWalk(git)) {
 				RevCommit c = rw.parseCommit(lastIndex);
 				oldTreeId = c.getTree();
 				tree = RefTree.read(rw.getObjectReader(), c.getTree());
 			}
 		}
 
 		PersonIdent committer = leader.getSystem().newCommitter(ts);
 		for (Proposal p : todo) {
 			if (!tree.apply(p.getCommands())) {
 				// This should not occur, previously during queuing the
 				// commands were successfully applied to the pending tree.
 				// Abort the entire round.
 				throw new IOException(
 						KetchText.get().queuedProposalFailedToApply);
 			}
 
 			ObjectId treeId = tree.writeTree(inserter);
 			if (treeId.equals(oldTreeId)) {
 				continue;
 			}
 
 			CommitBuilder b = new CommitBuilder();
 			b.setTreeId(treeId);
 			if (!ObjectId.zeroId().equals(lastIndex)) {
 				b.setParentId(lastIndex);
 			}
 			b.setAuthor(p.getAuthor() != null ? p.getAuthor() : committer);
 			b.setCommitter(committer);
 			b.setMessage(message(p));
 			lastIndex = inserter.insert(b);
 		}
 		if (lastIndex.equals(acceptedOldIndex)) {
 			throw new NoOp();
 		}
 		return lastIndex;
 	}
 
 	private String message(Proposal p) {
 		StringBuilder m = new StringBuilder();
 		String msg = p.getMessage();
 		if (msg != null && !msg.isEmpty()) {
 			m.append(msg);
 			while (m.length() < 2 || m.charAt(m.length() - 2) != '\n'
 					|| m.charAt(m.length() - 1) != '\n') {
 				m.append('\n');
 			}
 		}
 		m.append(KetchConstants.TERM.getName())
 				.append(": ") //$NON-NLS-1$
 				.append(leader.getTerm());
 		return m.toString();
 	}
 
 	void abort() {
 		for (Proposal p : todo) {
 			p.abort();
 		}
 	}
 
 	@Override
 	void success() {
 		for (Proposal p : todo) {
 			p.success();
 		}
 	}
 
 	private List<ReceiveCommand> makeStageList(Repository git,
 			ObjectInserter inserter) throws IOException {
 		// For each branch, collapse consecutive updates to only most recent,
 		// avoiding sending multiple objects in a rapid fast-forward chain, or
 		// rewritten content.
 		Map<String, ObjectId> byRef = new HashMap<>();
 		for (Proposal p : todo) {
 			for (Command c : p.getCommands()) {
 				Ref n = c.getNewRef();
 				if (n != null && !n.isSymbolic()) {
 					byRef.put(n.getName(), n.getObjectId());
 				}
 			}
 		}
 		if (byRef.isEmpty()) {
 			return Collections.emptyList();
 		}
 
 		Set<ObjectId> newObjs = new HashSet<>(byRef.values());
 		StageBuilder b = new StageBuilder(
 				leader.getSystem().getTxnStage(),
 				acceptedNewIndex);
 		return b.makeStageList(newObjs, git, inserter);
 	}
 
 	private void blockUntil(ProposedTimestamp ts)
 			throws TimeIsUncertainException {
 		List<ProposedTimestamp> times = todo.stream()
 				.flatMap(p -> p.getProposedTimestamps().stream())
 				.collect(Collectors.toCollection(ArrayList::new));
 		times.add(ts);
 
 		try {
 			Duration maxWait = getSystem().getMaxWaitForMonotonicClock();
 			ProposedTimestamp.blockUntil(times, maxWait);
 		} catch (InterruptedException | TimeoutException e) {
 			throw new TimeIsUncertainException(e);
 		}
 	}
 
 	private static class NoOp extends Exception {
 		private static final long serialVersionUID = 1L;
 	}
 }