--- a/src/org/tmatesoft/hg/internal/MergeStateBuilder.java	Fri Aug 16 14:54:09 2013 +0200
+++ b/src/org/tmatesoft/hg/internal/MergeStateBuilder.java	Fri Aug 16 19:22:59 2013 +0200
@@ -16,9 +16,24 @@
  */
 package org.tmatesoft.hg.internal;
 
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.tmatesoft.hg.core.HgFileRevision;
 import org.tmatesoft.hg.core.HgIOException;
+import org.tmatesoft.hg.core.Nodeid;
+import org.tmatesoft.hg.repo.HgManifest;
 import org.tmatesoft.hg.repo.HgMergeState;
+import org.tmatesoft.hg.repo.HgRepositoryFiles;
+import org.tmatesoft.hg.util.ByteChannel;
+import org.tmatesoft.hg.util.CancelledException;
 import org.tmatesoft.hg.util.Path;
+import org.tmatesoft.hg.util.LogFacility.Severity;
 
 /**
  * Constructs merge/state file
@@ -28,21 +43,139 @@
  * @author TMate Software Ltd.
  */
 public class MergeStateBuilder {
-	
+
 	private final Internals repo;
+	private final List<Record> unresolved = new ArrayList<Record>();
+	private Nodeid stateParent = Nodeid.NULL;
 
 	public MergeStateBuilder(Internals implRepo) {
 		repo = implRepo;
 	}
 	
+	public void prepare(Nodeid nodeid) {
+		assert nodeid != null;
+		unresolved.clear();
+		stateParent = nodeid;
+		abandon();
+	}
+	
 	public void resolved() {
 		throw Internals.notImplemented();
 	}
 
-	public void unresolved(Path file) {
-		throw Internals.notImplemented();
+	public void unresolved(Path file, HgFileRevision first, HgFileRevision second, HgFileRevision base, HgManifest.Flags flags) throws HgIOException {
+		Record r = new Record(file, first.getPath(), second.getPath(), base.getPath(), base.getRevision(), flags);
+		final File d = mergeStateDir();
+		d.mkdirs();
+		File f = new File(d, r.hash());
+		try {
+			FileOutputStream fos = new FileOutputStream(f);
+			first.putContentTo(new OutputStreamSink(fos));
+			fos.flush();
+			fos.close();
+			unresolved.add(r);
+		} catch (IOException ex) {
+			throw new HgIOException(String.format("Failed to write content of unresolved file %s to merge state at %s", file, f), f);
+		} catch (CancelledException ex) {
+			repo.getLog().dump(getClass(), Severity.Error, ex, "Our impl doesn't throw cancellation");
+		}
 	}
 
-	public void serialize(Transaction tr) throws HgIOException {
+	// merge/state serialization is not a part of a transaction
+	public void serialize() throws HgIOException {
+		if (unresolved.isEmpty()) {
+			return;
+		}
+		File mergeStateFile = repo.getRepositoryFile(HgRepositoryFiles.MergeState);
+		try {
+			final byte NL = '\n';
+			FileOutputStream fos = new FileOutputStream(mergeStateFile);
+			fos.write(stateParent.toString().getBytes());
+			fos.write(NL);
+			for(Record r : unresolved) {
+				fos.write(r.key.toString().getBytes());
+				fos.write(0);
+				fos.write('u');
+				fos.write(0);
+				fos.write(r.hash().toString().getBytes());
+				fos.write(0);
+				fos.write(r.fnameA.toString().getBytes());
+				fos.write(0);
+				fos.write(r.fnameAncestor.toString().getBytes());
+				fos.write(0);
+				fos.write(r.ancestorRev.toString().getBytes());
+				fos.write(0);
+				fos.write(r.fnameB.toString().getBytes());
+				fos.write(0);
+				fos.write(r.flags.mercurialString().getBytes());
+				fos.write(NL);
+			}
+			fos.flush();
+			fos.close();
+		} catch (IOException ex) {
+			throw new HgIOException("Failed to serialize merge state", mergeStateFile);
+		}
+	}
+	
+	public void abandon() {
+		File mergeStateDir = mergeStateDir();
+		try {
+			FileUtils.rmdir(mergeStateDir);
+		} catch (IOException ex) {
+			// ignore almost silently
+			repo.getLog().dump(getClass(), Severity.Warn, ex, String.format("Failed to delete merge state in %s", mergeStateDir));
+		}
+	}
+
+	private File mergeStateDir() {
+		return repo.getRepositoryFile(HgRepositoryFiles.MergeState).getParentFile();
+	}
+
+	private static class Record {
+		public final Path key;
+		public final Path fnameA, fnameB, fnameAncestor;
+		public final Nodeid ancestorRev;
+		public final HgManifest.Flags flags;
+		private String hash;
+
+		public Record(Path fname, Path a, Path b, Path ancestor, Nodeid rev, HgManifest.Flags f) {
+			key = fname;
+			fnameA = a;
+			fnameB = b;
+			fnameAncestor = ancestor;
+			ancestorRev = rev;
+			flags = f;
+		}
+		
+		public String hash() {
+			if (hash == null) {
+				hash = new DigestHelper().sha1(key).asHexString();
+			}
+			return hash;
+		}
+	}
+
+	private static class OutputStreamSink implements ByteChannel {
+		private final OutputStream out;
+
+		public OutputStreamSink(OutputStream outputStream) {
+			out = outputStream;
+		}
+
+		public int write(ByteBuffer buffer) throws IOException {
+			final int toWrite = buffer.remaining();
+			if (toWrite <= 0) {
+				return 0;
+			}
+			if (buffer.hasArray()) {
+				out.write(buffer.array(), buffer.arrayOffset(), toWrite);
+			} else {
+				while (buffer.hasRemaining()) {
+					out.write(buffer.get());
+				}
+			}
+			buffer.position(buffer.limit());
+			return toWrite;
+		}
 	}
 }